Combating Climate Change in the Kenyan Tea Industry

Effect of Shading on Physiological Attributes and Proteomic Analysis of Tea during Low Temperatures

Shading is an important technique to protect tea plantations under abiotic stresses. In this study, we analyzed the effect of shading (SD60% shade vs. SD0% no-shade) on the physiological attributes and proteomic analysis of tea leaves in November and December during low temperatures. The results revealed that shading protected the tea plants, including their soil plant analysis development (SPAD), photochemical efficiency (Fv/Fm), and nitrogen content (N), in November and December. The proteomics analysis of tea leaves was determined using tandem mass tags (TMT) technology and a total of 7263 proteins were accumulated. Further, statistical analysis and the fold change of significant proteins (FC < 0.67 and FC > 1.5 p < 0.05) revealed 14 DAPs, 11 increased and 3 decreased, in November (nCK_vs_nSD60), 20 DAPs, 7 increased and 13 decreased, in December (dCK_vs_dSD60), and 12 DAPs, 3 increased and 9 decreased, in both November and December (nCK_vs_nSD60). These differentially accumulated proteins (DAPs) were dehydrins (DHNs), late-embryogenesis abundant (LEA), thaumatin-like proteins (TLPs), glutathione S-transferase (GSTs), gibberellin-regulated proteins (GAs), proline-rich proteins (PRPs), cold and drought proteins (CORA-like), and early light-induced protein 1, which were found in the cytoplasm, nucleus, chloroplast, extra cell, and plasma membrane, and functioned in catalytic, cellular, stimulus-response, and metabolic pathways. In conclusion, the proliferation of key proteins was triggered by translation and posttranslational modifications, which might sustain membrane permeability in tea cellular compartments and could be responsible for tea protection under shading during low temperatures. This study aimed to investigate the impact of the conventional breeding technique (shading) and modern molecular technologies (proteomics) on tea plants, for the development and protection of new tea cultivars.

Genomic selection strategies to increase genetic gain in tea breeding programs

Tea [Camellia sinensis (L.) O. Kuntze] is mainly grown in low- to middle-income countries (LMIC) and is a global commodity. Breeding programs in these countries face the challenge of increasing genetic gain because the accuracy of selecting superior genotypes is low and resources are limited. Phenotypic selection (PS) is traditionally the primary method of developing improved tea varieties and can take over 16 yr. Genomic selection (GS) can be used to improve the efficiency of tea breeding by increasing selection accuracy and shortening the generation interval and breeding cycle. Our main objective was to investigate the potential of implementing GS in tea-breeding programs to speed up genetic progress despite the low cost of PS in LMIC. We used stochastic simulations to compare three GS-breeding programs with a Pedigree and PS program. The PS program mimicked a practical commercial tea-breeding program over a 40-yr breeding period. All the GS programs achieved at least 1.65 times higher genetic gains than the PS program and 1.4 times compared with Seed-Ped program. Seed-GSc was the most cost-effective strategy of implementing GS in tea-breeding programs. It introduces GS at the seedlings stage to increase selection accuracy early in the program and reduced the generation interval to 2 yr. The Seed-Ped program outperformed PS by 1.2 times and could be implemented where it is not possible to use GS. Our results indicate that GS could be used to improve genetic gain per unit time and cost even in cost-constrained tea-breeding programs.

Effect of seasonal variation on yield and leaf quality of tea clone (Camellia sinensis (L.) O. Kuntze) in South West Ethiopia

The tea plant is widely cultivated in southwest Ethiopia. But the impact of seasonal variation on monthly yield, leaf quality, and the long-term yield response potential of clones has not been studied. The objective of the study is to determine the impact of seasonal change and climate variables on the yield and leaf quality of tea plants in southwest Ethiopia. The experiment consisted of five clones and four seasons under a split-plot design and was replicated three times. The results indicated that the yield and leaf quality showed significant variation in the different seasons at P < 0.05. The highest peak yields of 12.68, 12.59, and 11.3 kg plot^-1 were recorded in May, June, and April, respectively, and the yield suddenly dropped by 5.1% in July. Then the soft banjhi increased by 5-10% in July. The yield response potential of clones is highly affected by monthly climate variation at P < 0.05. Clone BB-35 recorded the highest (18.8 kg plot^-1) yield in June, followed by clones 11/4 (18.3) in May, 11/56 (14.7) in November, 6/8 (11.7) in December, and 12/38 (5.78 kg plot^-1) in June. The lowest mean green leaf and a longer shoot replacement cycle were created due to a decrease in rainfall to 760 mm/month and rising temperatures above 26.35 °C in winter. The leaf phenological response of tea clones is strongly governed by the monthly temperature and suitable precipitation pattern of a season. The highlands have two harvesting seasons, i.e., a dry and a wet harvesting season. The dry harvesting season, which exists between the middle of December and March, accounts for 18.3-24.3% of the total annual yield. The wet harvesting season is subdivided further into two peak harvesting seasons. The first harvest is characterized by a short plucking round, and the highest peak yield occurs in April, May, and June, accounting for 40.22-42.2% of the total annual yield. The second wet harvesting season begins in September and ends in the middle of December, contributing to 35.5-40% of the annual yield. Seasonal variation has a direct impact on leaf quality and clone yielding potential. Clones show higher yield and shorter plucking rounds at maximum temperatures above 23.03 °C and below 26.35 °C, but temperatures above 28.34 °C and below 10.38 °C have a negative effect on leaf quality and yield. Over the last two decades, rainfall, maximum, and mean temperatures all increased by 16.09 mm y-1, 0.127 °C, and 0.0566 °C y^-1, respectively, and the tea plant showed a strong correlation with maximum temperature (76%), whereas mean temperature (44.6%) and annual rainfall (32.8%) correlated weakly. Green leaf production is well explained by around 85.4% of the observed climate variance, with an increase of 1287.18 tonnes y^-1, and highland tea production will exhibit a positive net benefit from expected climate change in the future.

A Novel LED Light Radiation Approach Enhances Growth in Green and Albino Tea Varieties

Light, as an energy source, has been proven to strongly affect photosynthesis and, thus, can regulate the yield and quality of tea leaves (Camellia sinensis L.). However, few comprehensive studies have investigated the synergistic effects of light wavelengths on tea growth and development in green and albino varieties. Thus, the objective of this study was to investigate different ratios of red, blue and yellow light and their effects on tea plants' growth and quality. In this study, Zhongcha108 (green variety) and Zhongbai4 (albino variety) were exposed to lights of different wavelengths for a photoperiod of 5 months under the following seven treatments: white light simulated from the solar spectrum, which served as the control, and L1 (red 75%, blue 15% and yellow 10%), L2 (red 60%, blue 30% and yellow 10%), L3 (red 45%, far-red light 15%, blue 30% and yellow 10%), L4 (red 55%, blue 25% and yellow 20%), L5 (red 45%, blue 45% and yellow 10%) and L6 (red 30%, blue 60% and yellow 10%), respectively. We examined how different ratios of red light, blue light and yellow light affected tea growth by investigating the photosynthesis response curve, chlorophyll content, leaf structure, growth parameters and quality. Our results showed that far-red light interacted with red, blue and yellow light (L3 treatments) and significantly promoted leaf photosynthesis by 48.51% in the green variety, Zhongcha108, compared with the control treatments, and the length of the new shoots, number of new leaves, internode length, new leaf area, new shoots biomass and leaf thickness increased by 70.43%, 32.64%, 25.97%, 15.61%, 76.39% and 13.30%, respectively. Additionally, the polyphenol in the green variety, Zhongcha108, was significantly increased by 15.6% compared to that of the plants subjected to the control treatment. In addition, for the albino variety Zhongbai4, the highest ratio of red light (L1 treatment) remarkably enhanced leaf photosynthesis by 50.48% compared with the plants under the control treatment, resulting in the greatest new shoot length, number of new leaves, internode length, new leaf area, new shoot biomass, leaf thickness and polyphenol in the albino variety, Zhongbai4, compared to those of the control treatments, which increased by 50.48%, 26.11%, 69.29%, 31.61%, 42.86% and 10.09%, respectively. Our study provided these new light modes to serve as a new agricultural method for the production of green and albino varieties.

The Role of Calmodulin Binding Transcription Activator in Plants under Different Stressors: Physiological, Biochemical, Molecular Mechanisms of Camellia sinensis and Its Current Progress of CAMTAs

Low temperatures have a negative effect on plant development. Plants that are exposed to cold temperatures undergo a cascade of physiological, biochemical, and molecular changes that activate several genes, transcription factors, and regulatory pathways. In this review, the physiological, biochemical, and molecular mechanisms of Camellia sinensis have been discussed. Calmodulin binding transcription activator (CAMTAs) by molecular means including transcription is one of the novel genes for plants' adaptation to different abiotic stresses, including low temperatures. Therefore, the role of CAMTAs in different plants has been discussed. The number of CAMTAs genes discussed here are playing a significant role in plants' adaptation to abiotic stress. The illustrated diagrams representing the mode of action of calcium (Ca²⁺) with CAMTAs have also been discussed. In short, Ca²⁺ channels or Ca²⁺ pumps trigger and induce the Ca²⁺ signatures in plant cells during abiotic stressors, including low temperatures. Ca²⁺ signatures act with CAMTAs in plant cells and are ultimately decoded by Ca²⁺sensors. To the best of our knowledge, this is the first review reporting CAMAT's current progress and potential role in C. sinensis, and this study opens a new road for researchers adapting tea plants to abiotic stress.

Hormonal regulation of health-promoting compounds in tea (Camellia sinensis L.)

Tea is the most frequently consumed natural beverage across the world produced with the young leaves and shoots of the evergreen perennial plant Camellia sinensis (L.) O. Kuntze. The expanding global appeal of tea is partly attributed to its health-promoting benefits such as anti-inflammation, anti-cancer, anti-allergy, anti-hypertension, anti-obesity, and anti- SARS-CoV-2 activity. The many advantages of healthy tea intake are linked to its bioactive substances such as tea polyphenols, flavonoids (catechins), amino acids (theanine), alkaloids (caffeine), anthocyanins, proanthocyanidins, etc. that are produced through secondary metabolic pathways. Phytohormones regulate secondary metabolite biosynthesis in a variety of plants, including tea. There is a strong hormonal response in the biosynthesis of polyphenols, catechins, theanine and caffeine in tea under control and perturbed environmental conditions. In addition to the impact of preharvest plant hormone manipulation on green tea quality, changes in hormones of postharvest tea also regulate quality-related metabolites in tea. In this review, we discuss the health benefits of major tea constituents and the role of various plant hormones in improving the endogenous levels of these compounds for human health benefits. The fact that the ratio of tea polyphenols to amino acids and the concentrations of tea components are changed by environmental conditions, most notably by climate change-associated variables, the selection and usage of optimal hormone combinations may aid in sustaining tea quality, and thus can be beneficial to both consumers and producers.

Color Shade Nets Affect Plant Growth and Seasonal Leaf Quality of Camellia sinensis Grown in Mississippi, the United States

Shading modifies the microenvironment and can provide plants with some protection from frequent heat, drought, frost, and hail induced by climate change and has the potential to improve plant growth, yield, and quality. Tea (Camellia sinensis) is an ancient plant originating from tropical and subtropical regions and prefers to grow in partial shade under the forest canopy. The emerging tea industry in the United States (US) requires research support on establishing tea fields in novel environmental conditions as well as on producing high-quality tea products. This study investigated the effects of black, blue, and red shade nets on tea plant growth and seasonal leaf qualities in the southeastern US with a humid subtropical climate. When compared to no-shade control, black, blue, and red shade nets increased plant growth index (PGI), net photosynthetic rate (P_n), and stomatal conductance (g_s), decreased air and leaf surface temperatures in summer, and reduced cold damage in winter. No significant difference was found among the black, blue, and red shade nets on tea plant growth. Varying contents of total polyphenols, carbohydrates, free amino acids, L-theanine, gallic acid, caffeine, and catechins in fresh tea leaves were observed among different shade treatments and harvesting seasons. 69.58% of the variations were depicted in a biplot by principal component analysis. Red shade was considered helpful for improving green tea quality by increasing the content of L-theanine and free amino acids in tea leaves collected in spring and fall when compared to no-shade control.

Molecular regulation of anthocyanin discoloration under water stress and high solar irradiance in pluckable shoots of purple tea cultivar

During water-deficit stress, antioxidant enzymes use anthocyanin molecules as co-substrates to scavenge for reactive oxygen species leading to reduced anthocyanin content and ultimately loss of purple leaf pigmentation in tea. Anthocyanins are an important class of flavonoids responsible for liquor color and market acceptability of processed tea from the anthocyanin-rich purple tea cultivar 'TRFK 306'. However, the color in pluckable shoots fade and turn green during the dry and hot season, before rapidly reverting back to purple when weather is favorably wet and cool/cold. Our study revealed that loss of purple leaf pigmentation correlated well with reduced precipitation, high soil water-deficit, increased intensity and duration of sunlight and temperature. Richly purple pigmented leaves harvested during the cool, wet conditions recorded significantly higher anthocyanin content compared to faded samples harvested during the dry season. Similarly, individual anthocyanins were affected by seasonal changes with malvidin being the most abundant. Comparative transcriptomics of two RNA-seq libraries, dry/discolored and wet/colored seasons, revealed depression of most metabolic processes related to anthocyanin accumulation in dry conditions. Specifically, transcripts encoding pathway regulators, MYB-bHLH-WD40 (MBW) complex, were repressed possibly contributing to the suppression of late biosynthetic genes of the pathway. Further, suppression of anthocyanin transport genes could be linked to reduced accumulation of anthocyanin in the vacuole during the dry season. However, slight increase in expression of some transporter and reactive oxygen species (ROS) antioxidant genes in the discolored leaf suggests non-enzymatic degradation of anthocyanin, ultimately leading to loss of purple color during the dry season. Based on increased expression of ROS antioxidant genes (especially catalase and superoxide dismutase) in the discolored leaf, we speculate that anthocyanins are used as co-substrates by antioxidant enzymes to scavenge for ROS (especially hydrogen peroxide) that escape from organelles, leading to reduced anthocyanins and loss of pigmentation during the dry season.

Underpinning the molecular programming attributing heat stress associated thermotolerance in tea (Camellia sinensis (L.) O. Kuntze)

The most daunting issue of global climate change is the deleterious impact of extreme temperatures on tea productivity and quality, which has resulted in a quest among researchers and growers. The current study aims to unravel molecular programming underpinning thermotolerance by characterizing heat tolerance and sensitivity response in 20 tea cultivars. The significantly higher negative influence of heat stress was recorded in a sensitive cultivar with reduced water retention (47%), chlorophyll content (33.79%), oxidation potential (32.48%), and increase in membrane damage (76.4%). Transcriptional profiling of most tolerant and sensitive cultivars identified 78 differentially expressed unigenes with chaperon domains, including low and high molecular weight heat shock protein (HSP) and heat shock transcription factors (HSFs) involved in heat shock response (HSR). Further, predicted transcriptional interactome network revealed their key role in thermotolerance via well-co-ordinated transcriptional regulation of aquaporins, starch metabolism, chlorophyll biosynthesis, calcium, and ethylene mediated plant signaling system. The study identified the key role of HSPs (CsHSP90) in regulating HSR in tea, wherein, structure-based molecular docking revealed the inhibitory role of geldanamycin (GDA) on CsHSP90 by blocking ATP binding site at N-terminal domain of predicted structure. Subsequently, GDA mediated leaf disc inhibitor assay further affirmed enhanced HSR with higher expression of CsHSP17.6, CsHSP70, HSP101, and CsHSFA2 genes in tea. Through the current study, efforts were made to extrapolate a deeper understanding of chaperons mediated regulation of HSR attributing thermotolerance in tea.

Transcriptional analysis reveals key insights into seasonal induced anthocyanin degradation and leaf color transition in purple tea (Camellia sinensis (L.) O. Kuntze)

Purple-tea, an anthocyanin rich cultivar has recently gained popularity due to its health benefits and captivating leaf appearance. However, the sustainability of purple pigmentation and anthocyanin content during production period is hampered by seasonal variation. To understand seasonal dependent anthocyanin pigmentation in purple tea, global transcriptional and anthocyanin profiling was carried out in tea shoots with two leaves and a bud harvested during in early (reddish purple: S1_RP), main (dark gray purple: S2_GP) and backend flush (moderately olive green: S3_G) seasons. Of the three seasons, maximum accumulation of total anthocyanin content was recorded in S2_GP, while least amount was recorded during S3_G. Reference based transcriptome assembly of 412 million quality reads resulted into 71,349 non-redundant transcripts with 6081 significant differentially expressed genes. Interestingly, key DEGs involved in anthocyanin biosynthesis [PAL, 4CL, F3H, DFR and UGT/UFGT], vacuolar trafficking [ABC, MATE and GST] transcriptional regulation [MYB, NAC, bHLH, WRKY and HMG] and Abscisic acid signaling pathway [PYL and PP2C] were significantly upregulated in S2_GP. Conversely, DEGs associated with anthocyanin degradation [Prx and lac], repressor TFs and key components of auxin and ethylene signaling pathways [ARF, AUX/IAA/SAUR, ETR, ERF, EBF1/2] exhibited significant upregulation in S3_G, correlating positively with reduced anthocyanin content and purple coloration. The present study for the first-time elucidated genome-wide transcriptional insights and hypothesized the involvement of anthocyanin biosynthesis activators/repressor and anthocyanin degrading genes via peroxidases and laccases during seasonal induced leaf color transition in purple tea. Futuristically, key candidate gene(s) identified here can be used for genetic engineering and molecular breeding of seasonal independent anthocyanin-rich tea cultivars.