INTRODUCTION

Coffea arabica also called as the Arabian coffee belongs to the Rubiaceae family and natives to tropical crop. This coffee cultivation and production is present throughout the world but majorly present in Brazil, Vietnam, Colombia, and Indonesia. The global production of coffee is 168.87million bags (http://www.ico.org/). C. arabica is originated from Ethiopia and today it is grown around the world (Söndahl et al., 2005) and is the 2^nd most commercial product followed by oil (Davis et al., 2012). South Korea’s coffee industry is also estimated at 6.8 trillion won in 2019. Korea is known a sixth consumption country in the world and an average adult drank average 353 cups in 2018 year (Park et al, 2019).

C. arabica is the polyploidy species of the genus Coffea and it contains 4 copies of 11 chromosomes, hybridization between the diploids C. canephora and C. eugenioides (Lashermes et al., 1999). It can endure low temperatures, but not frost, and it does best with a medial temperature between 15 and 24°C (Taye Kufa Obso, 2006). These beans of normal C. arabica have twelve milligram / gram of caffeine in dry mass and it contains 0.76 mg / gram of caffeine with all the flavor of the standard coffee beverage (Silvarolla et al., 2004). Coffee contains most of the medicinal values which is useful for human health.

Among some 90 species of the genus Coffea, due to disease and adaptability constraints and by other factors only two species are nowadays commercially grown worldwide, namely C. canephora (Robusta) will grow at low lands and C. arabica (Arabica) will grow at high lands altitude ranges between 1400 and 1800 m in tropical area (Da Matta & Ramalho, 2006;Dias et al., 2007; Hindorf et al., 2010; Davis et al. 2012). Due to some abnormal conditions (drought, high temperature, high cold and biotic stress), coffee production is going to decrease. To overcome these biotic and abiotic problems for mass production of high quality coffee breeding techniques MAS (Marker Assisted Selection) programme and genetic modifications techniques are useful. In this review, we discussed the impact of biotic and abiotic stress, the effect of environmental change on coffee plants and the genetic engineering approaches in coffee plants.

Suitable conditions, plant morphology and habitat

The temperature for the healthy survive of coffee plant is 15°C to 21°C and it can also tolerate the temperature up to 24°C. High temperature causes damage, eventually fruit set will be reduced. It needs both sun (not direct sun) and rain, needs shade in its growth phase when it starts the flowering and during fruit set (Franco, 1958;Camargo, 2010;Davis et al., 2012). Occurrence of frosts, even if sporadic, may strongly limit the economic success of the crop (Camargo, 1985;Camargo, 2009;Davis et al., 2012), moist and nutritionally rich soil, that is rapidly water storing and rapidly draining excess water from soil is suitable for the cultivation of coffee plants. Due to the rain falls and optimum temperature, the coffee plants were often planted on June to August. Lime will use in the soil to maintain pH 4.5 - 5.5. Coffee is a perennial bush with evergreen foliage, glossy appearance with main stem will grow vertically. Primary branches produce secondary, tertiary and lateral branches. In addition, some shoots arise from the main stem of the coffee plant and grow vertically; they are termed as ‘suckers' (Orthotropic shoots) and capable of forming a new bush by producing primary and secondary branches. The orthotropic shoots are also utilized for vegetative propagation. These plants develop very intense root system because of coffee roots expect more consumption of N, Ca, and Mg and its having self-pollination. Plants produce economic yields for 30 to 40 years on average with the height of 7-10 meters (Barwick et al., 2004). The plants, which will show the different morphology and physiology with high stress tolerant mechanism those varieties produce comparable yield under drought stress (Da Matta, 2004).

Effect of drought and high temperature on coffee production

Abiotic stress is the stress which can cause abnormal condition to plant by environmental factors like drought, high temperature, cold temperature, flooding, pollutants (ozone, sulfur dioxide), heavy metal and salt stress. Drought stress changes the physiology, morphology, metabolic, and molecular characters in plants. This stress occurs for several causes including limited rainfall and more intensity of light, evaporative demands and less wetness storage capacity of soils (Wery et al., 1994;Farooq et al., 2009;Salehi-Lisar et al., 2016). Drought can affect nearly every process in a plant, from energy production to grow and plants respond to drought stress through a variety of complex mechanisms (Levitt, 1980;Des Marais, 2017;Haile & Kang, 2018) and these coffee plants are more defenseless against to shortage of water stress during the propagative stages of extension (Growth), inflorescent and seed development. Consequently, plants will produce a few viable seeds (Tardieu et al., 2018). Limited water and unfavorable temperatures can arrest the plant metabolism and reduce the coffee yield.

High temperature also cause the stress which will change the plant phenomics and the temperature and photoperiod determine the distribution of a plant species by acting directly through physiological constraints (Growth and reproduction) (Thomas et al., 2004;Menendez et al., 2006;Silva et al., 2008). High-temperature stress has a major influence on plant reproduction, particularly those of microsporogenesis and megasporogenesis, anthesis, pollination, pollen tube growth, fertilization, and early embryo development. These are all highly susceptible to high-temperature stress. Due to failure of the above processes, plants will be decreased fertilization or increased early embryo abortion, led to a lower number of grains and limited yield (Weis & Berry, 1988;Da Matta et al., 2006;Silva et al., 2008;Farooq et al., 2009;Maduraimuthu & Vara Prasad, 2014;Naveed et al., 2014). This stress alters membrane functions by altering membrane fluidity and plant cell membrane structure which is especially important for crucial processes like light reactions and respiration. The formation of the flower and modification of flower into fruit set can be delayed by continuous exposure to temperatures up to over 30°C (86°F) and eventually it can severely damage coffee plants by stunting growth, yellowing leaves, even spawning stem tumors (Maduraimuthu & Vara Prasad, 2014).

In response to water limiting and high-temperature state, there is a change of gene expression will occur and it prompted by or operated by transcription factors (TFs). These TFs fasten to particular cis-elements to induce the expression of targeted stress-inducible genes, permitting for products to be transcribed that with stress response and tolerance (Nakashima et al., 2017), those includes DREB/ERF, AREBs, NAC, AP2/ERF, MYB, and WRKY. The cellular and signaling mechanism under the abiotic stress condition was shown in Fig.1.

The effect of abiotic stress on the coffee plant physiological and biochemical system

The abiotic stress (drought, salt, high temperature and cold) will change the plant physiological system including photosynthesis rate, chlorophyll content, stomatal index, specific leaf area, relative water content, water use efficiency, membrane stability and electrolyte leakage (Farooq et al. 2009;Mariga, 2016) hence plant cell may get damage and functions may not occur properly. The biochemical system in plants includes antioxidative enzymes (SOD, CAT, APX, and GR), proline, lipid peroxidation, total sugar levels, total amino acids, and soluble sugars are the major biochemical parameters in the plants system.

Photosynthesis can enlarge the biomass of plants. High rate of light reaction occurs for the excessive metabolisms and physiological changes for the excessive carbon fixation capacity (Gulmon & Chu, 1981). Although, Light intensity is the one which can change the photosynthetic rate, by applying the different temperature regimes to plants we can select the plants which are having the best photosynthetic rate under the high temperature (Mazzafera & Warrior, 1991;Bote & Struik, 2011;Biruk Ayalew, 2018;Liu et al., 2018). Likewise, Bote et al. (2018) reported that beneath of full sunlight, arabica scored a less rate of light reaction compared to the plants which were not grown under sun light. High shading reduces both quantity and quality of the passing of the radiation, hence reduces the morphology and physiological characters of the plant such as light reaction and extension (Morais et al., 2003;Bote & Struik, 2011;Biruk Ayalew, 2018). Eventually it reduces the stomatal conductivity hence occurs the less CO₂ intake and decline the light reaction of mesophyll cells by expose the plants to direct sun light and temperature (McDonald, 2003;Chastain et al., 2014;Tesfaye et al., 2014;Biruk Ayalew, 2018). Due to growing the plants under high shading climate it reduces the leaf surface temperature and leaf photosynthetic characteristics (Araujo et al., 2008;Steiman et al., 2011;Boreux et al., 2016;Liu et al., 2016; Nesper et al., 2017; Liu et al., 2018). Due to the decrease in the photosynthesis rate in plants automatically chlorophyll production also will be less, hence the plant's metabolism will become less compare to the plants which are having high photosynthetic rate coffee plants.

Light and CO₂ availability in the mesophyll of plant leaves are the main determinants of their net carbon assimilation rate. The coffee tree has low rates of net CO₂ assimilation (A) ranges of 4-11 mmol m^-2 s^-1 with current natural atmospheric CO₂ concentration. Da Matta et al. (2008) explained the rate of net carbondioxide assimilation by considering the ranges of stomatal conductance in arabica and conilon coffee. The average net carbondioxide assimilation (7.2 and 8.3 μmol m^-2 s^-1) was observed at 108 and 148 mmol m^-2 s^-1 of stomatal conductance. These two species determined the 30-40 μmol m^-2 s^-1 of photosynthesis under saturated light and CO₂ (~5 kPa) (Almeida & Maestri, 1997;Campostrini & Maestri, 1998;Da Matta et al., 2001;Silva et al., 2004). The developing green coffee fruits are also having stomata for gas exchange. The berry photosynthesis rate was increased at the photosynthetic photon flux range between 0 and 200 μmol photons m^-2 s^-1, and were nearly saturated at above 500 μmol photons m^-2 s^-1 (Vaast et al., 2005). By using the growth analysis, Cannel (1985) was reported that the photosynthesis in fruits is third of their own dry matter gain. Reis et al. (2009) reported that the plants provided 300kg ha^-1 of nitrogen showed high chlorophyll (72.78 μg L^-1) content and photosynthesis rate (15.43 μmol CO₂ m^-2 s^-1). Barros et al. (1999) was observed maximum rate of photosynthesis (4.5 mg CO₂ dm^-2 h^-1) and decreasing of photosynthesis by decreasing the stomatal conductance at midday. This is associated to stomatal closer induced by direct sun light in coffee plants. Ramalho et al. (2018) was reported that photosynthesis rate in three coffee species of ‘Apoata’, ‘Icatu’ and ‘Obata’ (2.8 μmol CO₂ m^-2 s^-1, 2 μmol CO₂ m^-2 s^-1 and 1.9 μmol CO₂ m^-2 s^-1) under drought and cold stress. Similarly, Pompelli et al. (2010) was discussed about high photosynthesis rate (2.1±2 μmol CO₂ m^-2 s^-1mol) under low light of low nitrogen (0 mmoles) and high nitrogen (23 mmoles) concentration. Kumar & Tieszen (1980) was observed that high photosynthesis rate (14 μmol CO₂ m^-2 s^-1) under shade leaves than the sun light leaves. Similar results were also reported that photosynthetic rate will be high in shaded leaves than under sun light leaves of coffee plants (Kumar & Tieszen 1980;Kaniechi et al., 1995;Paiva et al., 2003;Bote et al., 2018).

Stomata serve a very crucial function to plants, Stomata will get open during day time and close at the night time in coffee plants and they involve in the exchanging of gas, water transpiration and help for the photosynthesis to make energy for plant survival. Light, heat, water availability, atmospheric humidity, carbon dioxide concentration, and wind motions will directly affect stomatal movements (Martin et al., 1993;Kanechi et al., 1995;Wintgens, 2004;Taye Kufa & Jurgen Burkhardt, 2011). Leaves show a less stomatal opening due to the shortage of H₂O 20 - 30 mg cm^-2 of the surface of the leaf and close with a deficiency of about 80 mg cm^-2 in coffee plant. The evaporation of water from the non-shaded coffee plant is approximately 6 g cm^-2 (Ross-Karstens, 1998;Taye Kufa & Jurgen Burkhardt, 2011).

The stomatal conductance values were low as 10-20 mmol m^-2 s^-1 during the afternoon. The decreasing of net CO₂ assimilation rate in the afternoon has been associated with stomatal closure and also circumstantially with photo inhibition of photosynthesis (Da Matta et al., 2008). The coffee yields may decrease by increasing the more shade because of lower whole-tree carbon assimilation, that means more shade also will affect the coffee yield (Da Matta et al.,2008). The maximum and minimum stomatal densities were determined in full sunlight and moderate shade conditions respectively. In addition, the stomatal area index was significantly higher in sun-exposed leaves than in shaded leaves. Adugna & Paul (2011) was observed more stomatal conductance (100 mmol m^-2 s^-1) in shaded plants than the direct sun light (60 mmol m^-2 s^-1) plant leaves. Kumar & Tieszen (1980) and Kanechi et al. (1995) were observed lower stomatal conductance under sun light leaves due to increase of leaf temperature and vapor pressure. Similarly, Pompelli et al. (2010) was reported high stomatal conductance (19±0.7 mmol m⁻² s⁻¹ and 12±0.1 mmol m⁻² s⁻¹) at high light of high nitrogen and low nitrogen concentration.

Water use efficiency (WUE) was found to be higher in dry sites than in the wet sites thus reflecting the availability of water. The WUE is generally high in drought and hightemperature tolerant coffee varieties because these tolerant coffee varieties produce deep root system for uptake the water from the root system (Burkhardt et al., 2006;Abraham & Dufera, 2017;Liu et al., 2018). WUE is positively correlated with transpiration because of the water loss and gas exchange will occur high, so, that photosynthesis rate will become high (Meinzer et al., 1990;Da Matta et al., 2000;Pinheiro et al., 2005;Da Matta et al., 2006;Bote & Struik, 2011;Haggar et al., 2012;Dong et al., 2016).

Relative water content (RWC) is the method to check the water status for the physiological consequence of cellular water deficit and water potential as an estimate of the energy status of the plant. Water is more useful to explain the soil-plant–atmosphere condition. Water deficit plants contain more RWC in coffee plants under shade conditions to occur the freely plant metabolic mechanism (Nunes, 1976;Da Matta et al., 1993;Pinheiro et al., 2005;Pinheiro et al., 2005;Da Matta et al., 2006;Taye Kufa, 2006;Dias et al., 2007;Tounekti et al., 2018). High RWC increases photosynthesis through the chlorophyll content under stress conditions (Rodriguez et al. 2001;Matsumoto et al., 2006;Worku & Astatkie, 2010;Shimber et al., 2013). According to the Rodriguez et al. (2001) more relative water content was observed in the shaded plants than the direct sun light plants because the shaded plants contain more moisture content in soil and less transpiration from leaf. The chlorophyll content was also high in 70% sun light plants than the 100% sun light plants. Ramalho et al. (2018) was reported RWC in three coffee species of ‘Apoata’, ‘Icatu’ and ‘Obata’ (82.9±3%, 69.5 ± 3.4 % and 82.8±2.7%) under drought and cold stress, respectively. Haile & Kang (2018) was observed 74.6±1.80% of RWC in 40% deep sea water irrigated coffee seedlings.

Specific leaf area is one which will use in growth analysis and it can explain the link of plant carbon (C) and water cycles because it describes the diffusion of leaf biomass relative to leaf area. The specific leaf area is strongly affected by drought, high temperature and light intensity (Casper et al., 2001;Reich et al., 2002;Marron et al., 2003;Laureano et al., 2008;Farooq et al., 2009;Kumar et al., 2012;Liu et al., 2017). Adugna & Paul (2011) was observed more specific leaf area (116 cm² g⁻¹) in shaded plants than the direct sun light (98 cm² g⁻¹) plants.

Ion leakage is a good indication of the stress response in plant cells. This process widely used for the measurement of plant injury and plant stress tolerance (Levitt, 1972; Blum & Ebercon, 1981;Bajji et al., 2002; Demidchik et al., 2014). The accumulation of reactive oxygen species (ROS) in plant cell may lead to electrolyte leakage and often result in programmed cell death (Demidchik et al., 2014). The oozing of ions is specifically connected to potassium ions efflux from plant cells, which is mediated by plasma membrane cation conductance’s. Most probably the cation selectivity’s are encoded by GORK (Gated outwardly rectifier K⁺), SKOR (Stelar K⁺ outwardly rectifier), and annexin genes. CNG (Cyclic nucleotide-gated) and IGR (Ionotropic glutamate receptors) are ion channels also involved in ion movements. The general response of plant by drought, salt, and high-temperature flow chart was shown in Fig. 2. Haile & Kang (2018) was reported 90% of the electrolyte leakage in 40% deep sea water irrigated coffee seedlings. Similarly, Ursula et al. (1992) was observed 86% of the electrolyte leakage in response to water stress and gibberellic acid treated coffee plants. Chaves et al. (2017) was reported 3.8-4.0% of electrolyte leakage in seven years old of two-meter-tall coffee trees.

Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen. ROS is a set of free radicals, ions, and molecules obtained from oxygen (O₂) produced as byproducts of plant cellular metabolism. The most common ROS includes singlet oxygen (1O₂), superoxide anion (O₂^•−), hydrogen peroxide (H₂O₂), and hydroxyl radical (•OH^-). Environmental pressures lead to high production of ROS generates continuous oxidative damage eventually cell death. In plants, leakage of electrons into O₂ from the electron transport activities of chloroplasts, mitochondria, peroxisomes and plasma membranes (Foyer et al., 1994;Foyer et al., 1997;Del Río et al., 2006). ROS reacts with macromolecules (lipids, proteins, and DNA) to make the cells functionally inactive by causing the oxidative damage (Hiramoto et al., 1998;Foyer & Fletcher, 2001;Farooq et al., 2009;Sharma et al., 2012). For control or cleave, these toxic substances (detoxification) production of antioxidative enzymes occur in the plant cells. (Yan et al., 2007;Farooq et al., 2009;Sharma et al., 2012;Banavath et al., 2018). Those antioxidative enzymes are SOD (superoxide dismutase), CAT (catalase), GPX (Glutathione peroxidase), enzymes of ascorbate-glutathione (AsA-GSH) cycle such APX (Ascorbate peroxidase), MDHAR (Mono dehydro ascorbate reductase), DHAR (Dehydro ascorbate reductase), GR (Glutathione reductase) and GSH (glutathione). Non-enzymatic antioxidants are carotenoids, tocopherols, and phenolics (Rinkus et al., 1990;Devasagayam et al., 1996;Noctor et al., 1998;Asada, 1999;Sharma et al., 2010;Sharma et al., 2012;Martini et al., 2016; Metro et al., 2017).

Assemble of Proline in plant cell is one of the indication for the biochemical responses to various stress (biotic and abiotic) and it also involve in the developmental programme of generative tissues (e.g. pollen) (Chiang et al., 1995;Fabro et al., 2004;Verbruggen & Hermans, 2008). It acts as a multi-functional molecule and its defense by the stabilizing the protein structure by acts like molecular chaperon for the protecting the plant cell from the damaging effects of various environmental stresses. Besides acting as an excellent osmolyte, proline plays three major roles during stress, i.e. as a metal chelator, an antioxidative defense molecule and a signaling molecule (Jouve et al., 1993;Ashraf et al., 2007;Parvaiz & Satyawati, 2008;Szabados & Savouré, 2010;Palakolanu et al., 2011;Hayat et al., 2012;Koyro et al., 2012;De Carvalho et al., 2013;Banavath et al., 2018).

Da Matta et al. (1997) reported that proline accumulation is in C. arabica and C. canephora species of ‘Catui’ (5.65 μmol g^-1DM) and ‘Kouillou’ (8.24 μmol g^-1DM) in winter season, however ‘Catui’ (2.15 μmol g^-1DM) and ‘Kouillou’ (2.27 μmol g^-1DM) in summer season, respectively. Similarly, Jouve et al. (1993) reported accumulation of more proline in micro cuttings of arabica and canephora under low temperature. According to Mazzafera & Teixeira (1989), proline accumulation in drought-stressed plants of arabica coffee is more directly related to injury imposed by water limitation rather than being a defense mechanism against drought stress.

Soluble sugars are an important compound in maintain the fruitful structure and growth of the plants by participating in regulation of growth, light reaction, partitioning of carbon, metabolism of carbohydrate and lipids, osmotic homeostasis, protein synthesis and flowering, senescence, gene expression and stabilization of membranes during various abiotic stresses in coffee plants (Koch, 1996;Sheen et al., 1999;Smeekens, 2000;Hoekstra et al., 2001;Rolland & Sheen, 2006;Rosa et al., 2009) and involve in developmental process like embryogenesis to senescence’s (Franck et al.,2006;Knopp et al.,2006;Rolland et al., 2006;Geromel et al.,2008;Baliza et al.,2014). Chaves et al. (2017) reported the soluble sugars like starch (6.5 to 12.50 mmol kg^-1 FW), sucrose (4 to 7 mmol kg^-1 FW), and hexoses (3 to 10 mmol kg^-1 FW) in seven years old of 2- meter-tall coffee trees. Jouve et al. (1993) reported total soluble sugars in arabica and canephora coffees at different storage temperatures.

Impact of abiotic stress in coffee plant metabolism

During abiotic stress, the plants face the problems from environmental factors as discussed above, problems arise in plant cell metabolisms in a sequential manner to deplete the plant by producing the more ROS, decreasing the photosynthesis and reduced the production of soluble sugars, finally, the plant will die. Reactive oxygen species may react with the long chains of amino acid residues, Cholesterol and triglycerides and genetic materials (DNA and RNA), causing oxidative damage and impairing the normal functions of cells (Foyer & Fletcher, 2001). The important source for ROS is chloroplast because in thylakoid membranes the excited pigments may interact with O₂ to form strong oxidants such as O⁻² or O₁₂ (Niyogi, 1999). The electron transport chains of Photosystem-I (PSI) and photosystem-II (PS-II) are the major sources of ROS production and it is enhanced by conditions of limiting CO₂ fixation, during stress condition in the electron transport chain supplying of NADP decreased, that leakage of electrons occurs from ferredoxin to oxygen (O₂), reducing it to O₂^•− (Elstner, 1991; Asada, 2006; Siamsa et al., 2010;Shapiguzov et al., 2012;Sharma et al., 2012). This leakage of electrons to oxygen (O₂) may also happen from 2Fe-2S and 4Fe-4S clusters in the electron transport chain (ETC) of Photosynthesis-I (PS-I). Whereas in PS-II, the acceptor side of the electron transport chain has QA and QB. The production of O2^•− occurs from the leakage of electrons from QA and QB site to O₂, formation of this O2^•− by O₂ is a rate-limiting step.

In plants, the electron transport chain and ATP syntheses are tightly associated under ordinary aerobic conditions. Nevertheless, various stress factors lead to obstruction and modification of its components. Leading to over-demotion of electron carries at the low level production of ROS (Noctor et al., 2007;Blokhina & Fagerstedt, 2010;Siamsa et al., 2010). These have been implicated as secondary messengers in plant cells, including stomatal closure, programmed cell death, gravitropism (Jung et al., 2001;Mittler, 2002;Neill et al., 2002;Kwak et al., 2003;Yan et al., 2007).

Superoxide dismutase (SOD, 1.15.1.1) will play a major role in all aerobic organisms. This enzyme belongs to the group of metalloenzymes and catalyzes the dismutation of O₂^•− into oxygen (O₂) and hydrogen peroxide (H₂O₂). Three isozymes of SODs (Cu/Zn SOD), manganese superoxide dismutase and ferrous superoxide dismutase are announced in plants cells. All configurations of superoxide dismutase are nuclear-encoded for targeting to their particular subcellular compartments by an amino-terminal targeting sequence (Bowler et al., 1992;Racchi et al., 2001).

The first enzyme that is catalase (CAT, 1.11.1.6) was discovered and characterized. The tetrameric heme-containing catalase involves into the dismutation of two molecules of hydrogen peroxide into H₂O and O₂ (Del Río et al., 2006). Based on the expression pattern of the tobacco genes, catalase enzyme was classified in to three classes. Class-I catalases are expressed in photosynthetic tissues and regulated by light. Class-II catalases are expressed at greater levels in vascular tissues, although seed and young seedlings contain more about class-III catalase enzymes (Willekens et al., 1995).

Glutathione peroxidase (GPX, EC 1.11.1.7) enzyme contains four conserved disulfide bridges and two structural Ca²⁺ ions. Many isozymes of GPX are encoded by different genes and appeared in the cytosol, cell wall, and vacuoles. They can play a crucial role at formation and accumulation of lignin (lignification) in the cell wall, breakdown (degradation) of IAA, biosynthesis of ethylene, wound healing, and defense against biotic & abiotic stresses (Kobayashi et al., 1996).

Ramalho et al. (2018) studied about antioxidative enzyme activities in three coffee species under drought and cold stress plants. High SOD activity was found in ‘Obata’ (2,800 units g^-1 DW), ‘Icatu’ (4,300 units g^-1 DW) and ‘Apaota’ (2,500 units g^-1 DW). Catalase activity was appeared in ‘Obata’ (710 μmol H₂O₂ g^-1 DW min^-1), ‘Icatu’ (240 μmol H₂O₂ g^-1 DW min^-1) and ‘Apaota’ (170 μmol H₂O₂ g^-1 DW min^-1). Authors reported APX activity in ‘Obata’ (0.9 nmole ASC g^-1 DW min^-1), ‘Icatu’ (22 nmole ASC g^-1 DW min^-1) and ‘Apaota’ (10.3 nmole ASC g^-1 DW min^-1) and GR activity in ‘Obata’ (0.8 nmol NADPH g^-1 min^-1 DW), ‘Icatu’ (18 nmol NADPH g^-1 DW min^-1) and ‘Apaota’ (15 nmol NADPH g^-1 DW min^-1).

The Impact of biotic stress on coffee plants

In biotic stress, damage occurs by other living organisms, like bacteria, viruses, fungi, parasites, insects, weeds and cultivated or native plants. These agents consume the nutrients from the host and eventually reduce the plant vigor and in extreme cases, host plants get to die. When plants get affected continuously to biotic stress, causes changes of plant metabolism. Finally, physiological damages cause the less productivity. To overcome this problem, plants have developed an advanced protection mechanism. Thus, perception of plant protection mechanisms might stop the important crop and economic losses (Single & Krattinger, 2016; Gimenez et al., 2018). The problem which will occur by biotic stress is very critical to find immediately than abiotic stress. Whereas biotic stress is a little bit difficult to find the causative agent. But abiotic stress based on the symptoms can be identified easily than biotic stress.

Major fungal diseases in coffee plants are anthracnose (Colletotrichum gloeosporioides, C. kahawae), armillaria root rot (Armillaria mellea), brown eye spot (Cercospora coffeicola), coffee berry disease (CBD) (C. kahawae), Bark disease (Fusarium stilboides), berry blotch (C. coffeicola), red blister disease (C. coffeicola), coffee leaf rust (CLR, orange or leaf rust) (Hemileia vastatrix), coffee wilt disease (CWD), Gibberella xylarioides (Fusarium xylarioides). Among all of these fungal diseases CLR, CBD, and CWD, Gibberella xylarioides (F. xylarioides) diseases are majorly playing a role to decrease the coffee crop yield (Hindorf et al., 2011). Nematodes and parasitic disease is root-knot disease caused by Meloidogyne spp. Due to this biotic stress, the significant threat happens to agriculture and food security (Roberts, 2013). Due to the turmoil of environmental change, the plant tends to increased susceptibility to pathogens. Additionally, abiotic stress factors also damaging the plants, so that plants getting susceptibility to pathogenes (Garrett et al., 2006). By chewing the leaf by insects reduce the leaf area so that photosynthesis rate will be decreased and some vascular-wilt and fungi eradicate the water transport. Hence photosynthesis may be decreased by inducing stomatal closure (Flexas et al., 2012).

Effect of environmental change on coffee production

Due to global warming, agriculture related mitigations (production system and plant management) and agronomical adaptation (breeding programs) strategies may have different in the world (Camargo et al., 2010). Coffee cultivation is fraught with hazards of climate change, labor scarcity and global currency fluctuation. Some low scale production farmers are getting most trouble in cash flow issues which affect their capability to conduct timely cultivation. After harvesting the coffee crop, processing of the fruit till the beans stage is linked with economy. Hence, the coffee plantation sector requires support and small growers cannot be expected to cope with challenges such as global currency fluctuations. These growers, therefore, have to be supported through the mechanism of minimum support price and generous subsidies. To overcome the global warming problem, we need to produce the coffee plants by implementing the new agronomic techniques and genetic engineering methods to produce a good yield and quality of coffee crops. Those agronomical techniques include planting at more thickness, vegetated soil, irrigation and genetically breeding (Bergo et al., 2008). We can produce the high quality coffee beans by different adaptations and mitigation practices which include, using of medium shade crops or covering materials, re-construct the forest, genetic improvement and intercropping of coffee-banana plants and so on. Different conservation practices such as covering with grass species and secondary products of crops, which successfully supply both nutrients, and retains humidity of soil, thus decrease the water evaporation. Medium shade crops planting in the above-mentioned manner also improve soil water availability, nutrient enrichment and serve as a medium shade tree (Perfecto & Armbrecht, 2003; GACSA, 2015; Abraham et al., 2017). By digging the terraces, storing and preserving the rain water for future uses is one of the best method to increase the water potential (Lin, 2008; Kimemia, 2014).

Biotechnological aspects in improving the coffee production

Biotechnology is the science which deals the practical applications of biological organisms or their internal sub cellular compounds in agriculture, medical field, various agriculture industries and environmental management (Kasonta et al., 2002). To overcome the environmental challenges like abiotic stress and biotic stress, producing plants by using a biotechnological approach like molecular biology, genetic engineering, and plant tissue culture technology is most important (Carneiro et al., 1997;Ben miflin, 2000;Santana-Buzzy et al., 2007). Plant breeders use the technic to create a superior variety by taking genetic polymorphic plants with in each crop, and finally make them a huge quantity for economic purpose. Traditional breeders use classical genetic principles. This approach will take many years to incorporate desirable traits into crop varieties. Each parental line donates half of the genetic material to the progeny by traditional breeding. After several generations, the resulted unfavorable traits have to be exhausted. The progeny has to be tested in each generation to confirm the desired traits (Fazuoli et al., 2000;Ashebre, 2016;Banavath et al., 2018). This type of breeding aspect will take the long process, highly expensive, time taken and has to wait for many generations to get the desired traits. By using Modern agricultural biotechnological tools, the breeders can manipulate the genetic make-up of organisms and processing of agricultural products. Till now some transgenic coffee plants were developed to overcome the abiotic and biotic stress. Some of the genes which were transformed in the coffee plants are discussed below and the genes, promoters, reporter genes and explants for the study were shown in Table 1.

Abiotic tolerance genes in coffee

The C. canephora dehydration responsive element binding transcription factor (CcDREB1D) is a promoter, belongs to the dehydration responsive element binding (DREB) transcription factor family that involve majorly in controlling the expression of genes under abiotic and biotic stress. The transgenic C. arabica carrying this promoter showed tolerance to abiotic stress (water deficit) (Torres et al. 2016). DREB1D promoter haplotypes (HP15, HP16, and HP17) was shown the tolerance against abiotic stress (cold and water deficit) in C. arabica by regulating elements of this promoter involved in ABA-dependent, independent network, tissue specificity and in light regulations (Alves et al., 2017).

Biotic stress tolerance genes in coffee

Cry1Ac gene was isolated from Bacillus thuringiensis and it is one of the delta-endotoxins which act as insecticide. Cry 1Ac gene was transformed in C. canephora and C. arabica to protect from the pest that is the coffee leaf miner (Perileucoptera coffeella and Leucoptera spp.) (Leroy et al., 1999).

The WRKY1 (CaWRKY1) gene presented in C. arabica shows the tolerance against abiotic and biotic stress (Rust fungus Hemileia vastatrix). This gene contains CaWRKY1a and CaWRKY1b of two homologous genes identified in C. arabica allotetraploid genome (Anne et al., 2013). α-amylase inhibitor -1 gene (α-AI1) also protects the coffee plants from coffee berry borer insect-pest by Hypotheneumus hampei (Barbosa et al., 2010;Erika et al., 2015).

The bar reporter gene was cloned from Streptomyces bacteria this organism can produce the tri peptide bialaphos as a secondary metabolite. The bar gene has been used to engineer herbicide resistant plants. Cunha et al. (2004), Cruz et al. (2004) and Ribas et al. (2005) were cloned this bar gene in coffee plant tolerance to herbicide ammonium glufosinate.

β-glucuronidase (GUS) useful in the plant molecular biology system as a reporter gene. It can use for the identification and screening of transgenic coffee plants (Spiral & Petiard, 1991;Van Boxtel et al., 1995;Da silva & Yuffa, 2003;Rosillo et al., 2003).

Red fluorescent protein was taken from the coral Discosoma striata (DsRFP) and this gene was cloned in the coffee plant by Agrobacterium-mediated transformation. Red fluorescent protein was act as a reporter gene in the coffee plant (Canche-Moo et al., 2006). Hygromycin phosphotransferase (HptII) and rolA gene was transformed in C. canephora plants by A. rhizogenes (Vinod Kumar et al., 2006).

Some biotic stress tolerance genes are present in coffee plants. Those genes are cloned and characterization was done. C. arabica nonexpressor of pathogenesis-related gene 1 called CaNPR1. This gene played a major role in fungal diseases like coffee leaf rust caused by H. vastatrix. This nonexpressor of pathogenesis-related (NPR1) gene was shown homology in other crops (Cavallari et al., 2013), and it may play a wide role on biotic and abiotic stress tolerance in other crops (Silva et al., 2018).

Some genes in coffee plants will play role on biotic stress those genes are like GAPDH (SGN-U 347734, SGN-U 356404, 60S RPL7 and SGN-U351477), ADH (SGN-U 350348), UBQ (SGN-U 347154) and actin 7 plays role on diseases caused by H. vastatrix (Barsalobres- Cavallari et al., 2009;Joseph et al., 2018).

Some of the reference genes which are present in coffee plant tissues, expression studies were done from C. arabica (12 genes) and from C. canephora (8 genes). Those genes are ubiquitin (UBQ), Clathrin adaptor protein medium subunit (AP47), 60S ribosomal protein L39 (RPL39), elongation factor 1α (EF1α), class III alcohol dehydrogenase (ADH2), β-actin (ACT), glyceraldehyde 3- phosphate dehydrogenase (GAPDH), 24S (Ribosomal protein 24S), UBQ10, β-tubulin (TUB), Photosystem I P700 chlorophyll an Apo protein A2 (PSAB), caffeine synthase (DXMT), MDH and protein phosphatase 2A (PP2A) (Fernandes- Brum et al., 2017). Cavallari et al. (2009) was suggested that some internal control genes be useful for expression studies in C. arabica under different experimental conditions. Those genes are 60S ribosomal protein L7 (RPL7), ADH, 14-3-3, poly ubiquitin, β-actin and glyceraldehyde- 3-phosphate dehydrogenase. Cruz et al. (2009) also observed gene relative expression studies in coffee plants grown under abiotic stress conditions. Those genes are PsaB, PP2A, AP47, S24 (ribosomal protein), GAPDH, large ribosomal subunit 39 (rpl39), polyubiquitin 10 (UBQ10), ubiquitin-like protein (UBI9). Theobromine was a major intermediate product during the caffeine biosynthesis. This compound was studied with CaXMT1, CaMXMT1, CaMXMT2 and CaDXMT1 genes in coffee plants (Ogita et al., 2004). To understand the drought tolerance during the water deficit conditions, total 38 gene expression studies were done in two commercial cultivars (C. arabica cv. ‘IAPAR59’ and ‘IAPAR59’) (Mofatto et al., 2016). Similarly, to understand the light regulation mechanism in plants ribulose 1,5 bisphosphate carboxylase/oxygenase (RBCS1) promoter demonstrated as a leaf-specific and light-regulated promoter in tobacco plants (Marraccini et al., 2003).

The non-specific lipid transfer proteins (nsLTP) sequence was isolated from C. arabica and C. canephora for clone in tobacco plants to study the functional characterizations and genomic analysis (Cotta et al., 2014). The fulllength C. arabica domain-containing protein (CaBDP) gene sequence was extracted from RNA of drought-stressed C. arabica leaves. The gene was cloned in Arabidopsis to characterize the drought and salt tolerance in plants (Nguyen et al., 2016;Nguyen & Hunseung, 2017). Metallothionine proteins including CaMT4, CaMT15, CaMT3, and CaMT8 gene expression studies were done by treating the high and less copper (Cu) and zinc (Zn) nutrient solution to C. arabica plants, Main aim of this investigation was to study the role of metallothionine in the maintenance of Cu and Zn homeostasis and in detoxification of excessive levels of these nutrients (Bulgarelli et al., 2016).

Caffeine synthesis takes place by the action of xanthosine through N-methylation of C. arabica xanthosine methyltransferase 1 (CaXMT1), CaMXMT2, and CaDXMT1 genes (Uefuji et al., 2003). The coding for the 11Sglobulin seed storage protein (CSP1) of coffee gene was cloned in tobacco and promoter analysis and characterization was done (Marraccini et al., 1999). The coffee translation initiation factor Full name CaSUI1 gene was extracted from arabica beans during maturation and cloned for expression analysis finally observed the similarities with rice, maize and yeast SUI1 gene (Charlotte et al., 2003). During the drought conditions, the C. arabica homeobox 12 (CAHB12) gene was isolated from coffee for investigating the homeobox genes in the coffee genome project. Phylogenetic analysis (maximum likelihood method) described this CAHB12 gene is belongs to the Full name HD-ZIPL family and the expression pattern of CAHB12 gene in leaves and coffee roots was analyzed by real-time PCR (Priscilla et al., 2016).

Importance of coffee in medicine and health issues

Coffee contains 800 phenolic compounds are produced as secondary metabolites with aromatic rings, these compounds protect the plants from external environments (Monteiro et al., 2012). Alkaloids, terpenoids, carotenoids and some other enzymes are commonly present in coffee. Some important compounds like caffeic derivatives of poly phenols, p-coumaric derivative of cinnamic acid, vanillic, ferulic, and protocatechuic acid (Act on anti-inflammatory, anti tumoral, antispasmodica etc) are present in all coffee taxa (Stalikas et al., 2007). Moreover, beans contain 5-caffeoylquinic acid (5-CQA), feruloylquinic acids (3-, 4- and 5-FQA), the isomers of monoester, diester caffeoylquinic acids, various iridoid glycosides, dioxoanthracene (anthraquinonoids) and tannins (Mondolot et al. 2006;Wiart et al. 2006) are present. It's having so many medical importance’s for human beings to reduce the disease causative agents. It will decrease the ROS by increase the antioxidants in human body for the fight against which will involve in cellular damage to the heart diseases and some cancers (Ramalakshmi et al. 2008). Coffee reduces the feasibility of cancers of kidney, liver, premenopausal breast, and colon by the presence of caffeine, diterpenoid, caffeic acid, polyphenols, essential oil content, and heterocyclic molecules (Nkondjock, 2009). It will play a major role in gastrointestinal, dermatological, cardiovascular, nervous system and it will stimulate the respiratory system. It’s having antiviral, antifungal, antibacterial, anti-cellulitic, anti-aging, inflammatory and anti-allergic activity (Narayana et al., 2001;Boros et al., 2010;Kiran et al., 2011;Patay et al., 2016). The coffee fruit, leaf sap, flowers, and root saps were using for the treatment of the different types of diseases in many countries (Ghimire et al., 2009;Patay et al., 2016).

CONCLUSION

We have reviewed the effects of biotic, abiotic stress and crop management on the composition of coffee and the essential implications for quality and production. Coffee has a sufficient supply of instant energy so that the bean contains sufficient, good quality proteins and medicinal values. One aspect, in particular, that needs much more investigation to identify of various environmental stresses that affect coffee production and implicate for food safety. We also explained how these stresses interact with genetic factors and will be affected by climate change. This review explained the better understanding of the defense mechanism against oxidative stress. Most of the area cultivated coffee plants are attacked by different pathogens; hence more precautions have to be taken for coffee crop protection. Explained in detail climate change effects on coffee production and advantages of biotechnological aspects include molecular biology and genetic engineering aspects to improve the crop productivity.

적 요

커피(Coffea L.)는 꼭두서니과에 속하는 열대지역 농가의 대 표적인 경제작물로서 많은 단백질(25–28%)과 의학적 가치를 가지고 있다. 커피는 환경에 민감한 작물로서 기후변화는 커 피의 품질과 안정적 생산에 중대한 영향을 미친다. 커피에서 저항성 반응에 대한 비생물학적 baroreceptor를 개발하기 위해 다양한 생육단계, 그리고 여러가지 스트레스 조건하에서 생산 성을 높이기 위한 많은 연구가 이루지지고 있다. 다양한 생리 학적, 생태학적 및 생화학적 파라미터들은 커피의 생산성과 품 질을 변화시킨다. 이 논문은 커피에서 중요한 생물학적 및 비 생물학적 저항성에 대한 고찰을 실시하였다. 또한 커피의 생 산성 향상을 위한 최선의 이행방법과 약리학적인 가치, 그리 고 작물개량을 위한 생명공학적 접근방법을 제시하였다.