Tea green leafhopper infestations affect tea plant growth by altering the synthesis of brassinolide.

Tea green leafhoppers are insects widely distributed in major tea-growing areas. At present, less attention has been paid to the study on effect of tea green leafhopper infestation on tea growth phenotype. In this study, tea green leafhoppers were used to treat tea branches in laboratory and co-treated with brassinolide (BL), the highest bioactivity of brassinosteroids (BRs), in tea garden. The results showed that the expression of genes related to BRs synthesis was inhibited and BL content was reduced in tea shoots after infestation by tea green leafhoppers. In addition, area of each leaf position, length and diameter of internodes, and the biomass of the tender shoots of tea plant were decreased after infestation by tea green leafhoppers. The number of trichomes, leaf thickness, palisade tissue thickness and cuticle thickness of tea shoots were increased after tea green leafhoppers infestation. BL spraying could partially recover the phenotypic changes of tea branches caused by tea green leafhoppers infestation. Further studies showed that tea green leafhoppers infestation may regulate the expression of CsDWF4 (a key gene for BL synthesis) through transcription factors CsFP1 and CsTCP1a, which finally affect the BL content. Moreover, BL was applied to inhibit the tea green leafhoppers infestation on tea shoots. In conclusion, our study revealed the effect of plant hormone BL-mediated tea green leafhoppers infestation on the growth phenotype of tea plants.

The Circadian Clock Gene PHYTOCLOCK1 Mediates the Diurnal Emission of the Anti-Insect Volatile Benzyl Nitrile from Damaged Tea (Camellia sinensis) Plants.

Benzyl nitrile from tea plants attacked by various pests displays a diurnal pattern, which may be closely regulated by the endogenous circadian clock. However, the molecular mechanism by the circadian clock of tea plants that regulates the biosynthesis and release of volatiles remains unclear. In this study, the circadian clock gene CsPCL1 can activate both the expression of the benzyl nitrile biosynthesis-related gene CsCYP79 and the jasmonic acid signaling-related transcription factor CsMYC2 involved in upregulating CsCYP79 gene, thereby resulting in the accumulation and release of benzyl nitrile. Therefore, the anti-insect function of benzyl nitrile was explored in the laboratory. The application of slow-release beads of benzyl nitrile in tea plantations significantly reduced the number of tea geometrids and had positive effects on the yield of fresh tea leaves. These findings reveal the potential utility of herbivore-induced plant volatiles for the green control of pests in tea plantations.

Administrative Model for Profiling Hospital Performance on Coronary Artery Bypass Graft Surgery: Based on the Chinese Hospital Quality Monitoring System.

BACKGROUND: We aimed to develop an administrative model to profile the performance on the outcomes of coronary artery bypass grafting across hospitals in China. METHODS AND RESULTS: This retrospective study was based on the Chinese Hospital Quality Monitoring System (HQMS) from 2016 to 2020. The coronary artery bypass grafting cases were identified by procedure code, and those of 2016 to 2017 were randomly divided into modeling and validation cohorts, while those in other years were used to ensure the model stability across years. The outcome was discharge status as "death or withdrawal," and that withdrawal referred to discharge without medical advice when patients were in the terminal stage but reluctant to die in the hospital. Candidate covariates were mainly identified by diagnoses or procedures codes. Patient-level logistic models and hospital-level hierarchical models were established. A total of 203 010 coronary artery bypass grafts in 699 hospitals were included, with 60 704 and 20 233 cases in the modeling and validation cohorts and 40 423, 42 698, and 38 952 in the years 2018, 2019, and 2020, respectively. The death or withdrawal rate was 3.4%. The areas under the curve were 0.746 and 0.729 in the patient-level models of modeling and validation cohorts, respectively, with good calibration and stability across years. Hospital-specific risk-standardized death or withdrawal rates were 2.61% (interquartile range, 1.87%-3.99%) and 2.63% (interquartile range, 1.97%-3.44%) in the modeling and validation cohorts, which were highly correlated (correlation coefficient, 0.96; P<0.001). Between-hospital variations were distinguished among hospitals of different volumes and across years. CONCLUSIONS: The administrative model based on Hospital Quality Monitoring System could profile hospital performance on coronary artery bypass grafting in China.

Impact of High Lipoprotein(a) on Long-Term Survival Following Coronary Artery Bypass Grafting.

BACKGROUND: Lipoprotein(a) is a possible causal risk factor for atherosclerosis and related complications. The distribution and prognostic implication of lipoprotein(a) in patients undergoing coronary artery bypass grafting remain unknown. This study aimed to assess the impact of high lipoprotein(a) on the long-term prognosis of patients undergoing coronary artery bypass grafting. METHODS AND RESULTS: Consecutive patients with stable coronary artery disease who underwent isolated coronary artery bypass grafting from January 2013 to December 2018 from a single-center cohort were included. The primary outcome was all-cause death. The secondary outcome was a composite of major adverse cardiovascular and cerebrovascular events. Of the 18 544 patients, 4072 (22.0%) were identified as the high-lipoprotein(a) group (≥50 mg/dL). During a median follow-up of 3.2 years, primary outcomes occurred in 587 patients. High lipoprotein(a) was associated with increased risk of all-cause death (high lipoprotein(a) versus low lipoprotein(a): adjusted hazard ratio [aHR], 1.31 [95% CI, 1.09-1.59]; P=0.005; lipoprotein(a) per 1-mg/dL increase: aHR, 1.003 [95% CI, 1.001-1.006]; P=0.011) and major adverse cardiovascular and cerebrovascular events (high lipoprotein(a) versus low lipoprotein(a): aHR, 1.18 [95% CI, 1.06-1.33]; P=0.004; lipoprotein(a) per 1-mg/dL increase: aHR, 1.002 [95% CI, 1.001-1.004]; P=0.002). The lipoprotein(a)-related risk was greater in patients with European System for Cardiac Operative Risk Evaluation <3, and tended to attenuate in patients receiving arterial grafts. CONCLUSIONS: More than 1 in 5 patients with stable coronary artery disease who underwent coronary artery bypass grafting were exposed to high lipoprotein(a), which is associated with higher risks of death and major adverse cardiovascular and cerebrovascular events. The adverse effects of lipoprotein(a) were more pronounced in patients with clinically low-risk profiles or not receiving arterial grafts.

Effect of the biosynthesis of the volatile compound phenylacetaldehyde on chloroplast modifications in tea (Camellia sinensis) plants.

Plant volatile compounds have important physiological and ecological functions. Phenylacetaldehyde (PAld), a volatile phenylpropanoid/benzenoid, accumulates in the leaves of tea (Camellia sinensis) plants grown under continuous shading. This study was conducted to determine whether PAld production is correlated with light and to elucidate the physiological functions of PAld in tea plants. Specifically, the upstream mechanism modulating PAld biosynthesis in tea plants under different light conditions as well as the effects of PAld on chloroplast/chlorophyll were investigated. The biosynthesis of PAld was inhibited under light, whereas it was induced in darkness. The structural gene encoding aromatic amino acid aminotransferase 1 (CsAAAT1) was expressed at a high level in darkness, consistent with its importance for PAld accumulation. Additionally, the results of a transcriptional activation assay and an electrophoretic mobility shift assay indicated CsAAAT1 expression was slightly activated by phytochrome-interacting factor 3-2 (CsPIF3-2), which is a light-responsive transcription factor. Furthermore, PAld might promote the excitation of chlorophyll in dark-treated chloroplasts and mediate electron energy transfer in cells. However, the accumulated PAld can degrade chloroplasts and chlorophyll, with potentially detrimental effects on photosynthesis. Moreover, PAld biosynthesis is inhibited in tea leaves by red and blue light, thereby decreasing the adverse effects of PAld on chloroplasts during daytime. In conclusion, the regulated biosynthesis of PAld in tea plants under light and in darkness leads to chloroplast modifications. The results of this study have expanded our understanding of the biosynthesis and functions of volatile phenylpropanoids/benzenoids in tea leaves.

Light induces an increasing release of benzyl nitrile against diurnal herbivore Ectropis grisescens Warren attack in tea (Camellia sinensis) plants.

Herbivore-induced plant volatiles (HIPVs) are critical compounds that directly or indirectly regulate the tritrophic interactions among herbivores, natural enemies and plants. The synthesis and release of HIPVs are regulated by many biotic and abiotic factors. However, the mechanism by which multiple factors synergistically affect HIPVs release remains unclear. Tea plant (Camellia sinensis) is the object of this study because of its rich and varied volatile metabolites. In this study, benzyl nitrile was released from herbivore-attacked tea plants more in the daytime than at night, which was consistent with the feeding behaviour of tea geometrid (Ectropis grisescens Warren) larvae. The Y-tube olfactometer assay and insect resistance analysis revealed that benzyl nitrile can repel tea geometrid larvae and inhibit their growth. On the basis of enzyme activities in transiently transformed Nicotiana benthamiana plants, CsCYP79 was identified as a crucial regulator in the benzyl nitrile biosynthetic pathway. Light signalling-related transcription factor CsPIF1-like and the jasmonic acid (JA) signalling-related transcription factor CsMYC2 serve as the activator of CsCYP79 under light and damage conditions. Our study revealed that light (abiotic factor) and herbivore-induced damage (biotic stress) synergistically regulate the synthesis and release of benzyl nitrile to protect plants from diurnal herbivorous tea geometrid larvae.

Regulation of chlorophyll biosynthesis by light-dependent acetylation of NADPH:protochlorophyll oxidoreductase A in Arabidopsis.

Chlorophylls are the major pigments that harvest light energy during photosynthesis in plants. Although reactions in chlorophyll biogenesis have been largely known, little attention has been paid to the post-translational regulation mechanism of this process. In this study, we found that four lysine sites (K128/340/350/390) of NADPH:protochlorophyllide oxidoreductase A (PORA), which catalyzes the only light-triggered step in chlorophyll biosynthesis, were acetylated after dark-grown seedlings transferred to light via acetylomics analysis. Etiolated seedlings with K390 mutation of PORA had a lower greening rate and decreased PORA acetylation after illumination. Importantly, K390 of PORA was found extremely conserved in plants and cyanobacteria via bioinformatics analysis. We further demonstrated that the acetylation level of PORA was increased by exposing the dark-grown seedlings to the histone deacetylase (HDAC) inhibitor TSA. Thus, the HDACs probably regulate the acetylation of PORA, thereby controlling this non-histone substrate to catalyze the reduction of Pchlide to produce chlorophyllide, which provides a novel regulatory mechanism by which the plant actively tunes chlorophyll biosynthesis during the conversion from skotomorphogenesis to photomorphogenesis.

The Histone H3K27 Demethylase REF6 Is a Positive Regulator of Light-Initiated Seed Germination in Arabidopsis.

Seed germination is the first step in initiating a new life cycle in seed plants. Light is a major environmental factor affecting seed germination. Phytochrome B (phyB) is the primary photoreceptor promoting germination during the initial phase of imbibition. Post-translational histone methylation occurring at both lysine and arginine residues plays a crucial role in transcriptional regulation in plants. However, the role of histone lysine demethylation in light-initiated seed germination is not yet reported. Here, we identified that Relative of Early Flowering 6 (REF6)/Jumonji Domain-containing Protein 12 (JMJ12), a histone H3 lysine 27 (H3K27) demethylase, acts as a positive regulator of light-initiated seed germination. The loss of function of REF6 in Arabidopsis inhibits phyB-dependent seed germination. Genome-wide RNA-sequencing analysis revealed that REF6 regulates about half of the light-responsive transcriptome in imbibed seeds, including genes related to multiple hormonal signaling pathways and cellular processes. Phenotypic analyses indicated that REF6 not only regulates seed germination through GA (gibberellin) and ABA (abscisic acid) processes but also depends on the auxin signaling pathway. Furthermore, REF6 directly binds to and decreases the histone H3K27me3 levels of auxin-signaling- and cell-wall-loosening-related genes, leading to the activated expression of these genes in imbibed seeds. Taken together, our study identifies REF6 as the first histone lysine demethylase required for light-initiated seed germination. Our work also reveals the important role of REF6-mediated histone H3K27 demethylation in transcriptional reprogramming in the light-initiated seed germination process.

Outcome differences between surgeons performing first and subsequent coronary artery bypass grafting procedures in a day: a retrospective comparative cohort study.

BACKGROUND: With increasing surgical workload, it is common for cardiac surgeons to perform coronary artery bypass grafting (CABG) after other procedures in a workday. To investigate whether prior procedures performed by the surgeon impact the outcomes, we compared the outcomes between CABGs performed first versus those performed after prior procedures, separately for on-pump and off-pump CABGs as they differed in technical complexity. METHODS: We conducted a retrospective cohort study of patients undergoing isolated CABG in China from January 2013 to December 2018. Patients were categorised as undergoing on-pump and off-pump CABGs. Outcomes of the procedures performed first in primary surgeons' daily schedule (first procedure) were compared with subsequent ones (non-first procedure). The primary outcome was an adverse events composite (AEC) defined as the number of adverse events, including in-hospital mortality, myocardial infarction, stroke, acute kidney injury and reoperation. Secondary outcomes were the individual components of the primary outcome, presented as binary variables. Mixed-effects models were used, adjusting for patient and surgeon-level characteristics and year of surgery. RESULTS: Among 21 866 patients, 10 109 (16.1% as non-first) underwent on-pump and 11 757 (29.6% as non-first) off-pump CABG. In the on-pump cohort, there was no significant association between procedure order and the outcomes (all p>0.05). In the off-pump cohort, non-first procedures were associated with an increased number of AEC (adjusted rate ratio 1.29, 95% CI 1.13 to 1.47, p<0.001), myocardial infarction (adjusted OR (ORadj) 1.43, 95% CI 1.13 to 1.81, p=0.003) and stroke (ORadj 1.73, 95% CI 1.18 to 2.53, p=0.005) compared with first procedures. These increases were only found to be statistically significant when the procedure was performed by surgeons with <20 years' practice or surgeons with a preindex volume <700 cases. CONCLUSIONS: For a technically challenging surgical procedure like off-pump CABG, prior workload adversely affected patient outcomes.

Histone deacetylase CsHDA6 mediates the regulated formation of the anti-insect metabolite α-farnesene in tea (Camellia sinensis).

α-Farnesene accumulated in tea plants following infestations by most insects, and mechanical wounding is the common factor. However, the specific mechanism underlying the wounding-regulated accumulation of α-farnesene in tea plants remains unclear. In this study, we observed that histone deacetylase inhibitor treatment induced the accumulation of α-farnesene. The histone deacetylase CsHDA6 interacted directly with CsMYC2, which was an important transcription factor in the jasmonic acid (JA) pathway, and co-regulated the expression of the key α-farnesene synthesis gene CsAFS. Wounding caused by insect infestation affected CsHDA6 production at the transcript and protein levels, while also inhibited the binding of CsHDA6 to the CsAFS promoter. The resulting increased acetylation of histones H3/H4 in CsAFS enhanced the expression of CsAFS and the accumulation of α-farnesene. In conclusion, our study demonstrated the effect of histone acetylation on the production of tea plant HIPVs and revealed the importance of the CsHDA6-CsMYC2 transcriptional regulatory module.

Histone Deacetylase HDA15 Restrains PHYB-Dependent Seed Germination via Directly Repressing GA20ox1/2 Gene Expression.

Seed germination is essential for the colonization of the land plants. Light is a major environmental factor affecting seed germination, which is predominantly regulated by photoreceptor phytochrome B (PHYB). PHYB is activated by red light (designated as PHYB-on) whereas it is inactivated by far-red light (referred as PHYB-off). We previously reported that Arabidopsis histone deacetylase HDA15 interacts with phytochrome-interacting factor1 (PIF1) to repress seed germination under PHYB-off conditions. Here, we show that HDA15 plays a negative role in regulating seed germination under PHYB-on conditions. Overexpression of HDA15 in Arabidopsis restrains PHYB-dependent seed germination, while gibberellin (GA) relieves the repressive role of HDA15 under PHYB-off conditions. We further show that HDA15 directly binds to GA20ox1 and GA20ox2, two key GA biosynthesis genes and represses their expression by removal of histone H3 and H4 acetylation. Moreover, the levels of HDA15 transcript and HDA15 protein are up-regulated in the phyB mutant. Collectively, our work proposes that HDA15 acts as a negative regulator of PHYB-dependent seed germination by directly repressing GA20ox1/2 gene expression.

Involvement of histone deacetylase CsHDA2 in regulating (E)-nerolidol formation in tea (Camellia sinensis) exposed to tea green leafhopper infestation.

Herbivore-induced plant volatiles (HIPVs) help the tea plant (Camellia sinensis) adapt to environmental stress, and they are also quality-related components of tea. However, the upstream mechanism regulating the herbivore-induced expression of volatile biosynthesis genes is unclear, especially at the level of epigenetic regulation. In this study, similar to the effects of a tea green leafhopper infestation, treatments with exogenous jasmonic acid (JA) and histone deacetylase inhibitors significantly increased the (E)-nerolidol content in tea and induced the expression of the associated biosynthesis gene CsNES. Furthermore, a key transcription factor related to JA signaling, myelocytomatosis 2 (CsMYC2), interacted with histone deacetylase 2 (CsHDA2) in vitro and in vivo. A tea green leafhopper infestation inhibited CsHDA2 expression and decreased CsHDA2 abundance. Moreover, the tea green leafhopper infestation increased H3 and H4 acetylation levels in the promoter region of CsNES, which in turn upregulated the expression of CsNES and increased the (E)-nerolidol content. In this study, we revealed the effects of histone acetylations on the accumulation of HIPVs, while also confirming that CsHDA2-CsMYC2 is an important transcriptional regulatory module for the accumulation of (E)-nerolidol induced by tea green leafhoppers. The results of this study may be useful for characterizing plant aromatic compounds and the main upstream stress-responsive signaling molecules. Furthermore, the study findings will assist researchers clarify the epigenetic regulation influencing plant secondary metabolism in response to external stress.

Histone H3K27 demethylase SlJMJ4 promotes dark- and ABA- induced leaf senescence in tomato.

Leaf senescence is a highly-programmed developmental process during the plant life cycle. ABA plays an important role in leaf senescence. However, the mechanism underlying ABA-mediated leaf senescence, particularly the upstream epigenetic regulatory network, remains largely unclear. Here, we identified that SlJMJ4, a Jumonji C (jmjC) domain-containing protein in tomato, specifically demethylates di- and tri-methylations of lysine 27 of histone H3 (H3K27) in vitro and in vivo. Overexpression of SlJMJ4 results in premature senescence phenotype and promotes dark- and ABA-induced leaf senescence in tomato. Under dark condition, SlJMJ4-promoted leaf senescence is associated with upregulated expression of transcription factors (SlORE1 and SlNAP2) and senescence-associated genes (SlSAG113, SlSAG12) via removal of H3K27me3. In responses to ABA, overexpression of SlJMJ4 increases its binding at the loci of SlORE1, SlNAP2, SlSAG113, SlSAG12, SlABI5 and SlNCED3 and decreases their H3K27me3 levels, and therefore activates their expression and mediates ABA-induced leaf senescence in tomato. Taken together, these results demonstrate that SlJMJ4 plays a positive role in leaf senescence in tomato and is implicated in ABA-induced leaf senescence by binding to many key genes related to ABA synthesis and signaling, transcription regulation and senescence and hence promoting their H3K27me3 demethylation.

Mechanism Underlying the Shading-Induced Chlorophyll Accumulation in Tea Leaves.

Besides aroma and taste, the color of dry tea leaves, tea infusion, and infused tea leaves is also an important index for tea quality. Shading can significantly increase the chlorophyll content of tea leaves, leading to enhanced tea leaf coloration. However, the underlying regulatory mechanism remains unclear. In this study, we revealed that the expressions of chlorophyll synthesis genes were significantly induced by shading, specially, the gene encoding protochlorophyllide oxidoreductase (CsPOR). Indoor control experiment showed that decreased light intensity could significantly induce the expression of CsPOR, and thus cause the increase of chlorophyll content. Subsequently, we explored the light signaling pathway transcription factors regulating chlorophyll synthesis, including CsPIFs and CsHY5. Through expression level and subcellular localization analysis, we found that CsPIF3-2, CsPIF7-1, and CsHY5 may be candidate transcriptional regulators. Transcriptional activation experiments proved that CsHY5 inhibits CsPORL-2 transcription. In summary, we concluded that shading might promote the expression of CsPORL-2 by inhibiting the expression of CsHY5, leading to high accumulation of chlorophyll in tea leaves. The results of this study provide insights into the mechanism regulating the improvements to tea plant quality caused by shading.

Feasible strategies for studying the involvement of DNA methylation and histone acetylation in the stress-induced formation of quality-related metabolites in tea (Camellia sinensis).

Tea plants are subjected to multiple stresses during growth, development, and postharvest processing, which affects levels of secondary metabolites in leaves and influences tea functional properties and quality. Most studies on secondary metabolism in tea have focused on gene, protein, and metabolite levels, whereas upstream regulatory mechanisms remain unclear. In this review, we exemplify DNA methylation and histone acetylation, summarize the important regulatory effects that epigenetic modifications have on plant secondary metabolism, and discuss feasible research strategies to elucidate the underlying specific epigenetic mechanisms of secondary metabolism regulation in tea. This information will help researchers investigate the epigenetic regulation of secondary metabolism in tea, providing key epigenetic data that can be used for future tea genetic breeding.

Trends of Coronary Artery Bypass Grafting Performance in a Cohort of Hospitals in China Between 2013 and 2018.

BACKGROUND: China has witnessed a rapid increase in the volume of coronary artery bypass grafting (CABG) but substantial gaps in the performance for CABG across the nation. The present study aimed to investigate the change in CABG performance after years of quality improvement measures in a national registry in China. METHODS: The study included 66 971 patients who underwent isolated CABG in a cohort of 74 tertiary hospitals in China between January 2013 and December 2018. Data were collected from the Chinese Cardiac Surgery Registry. Outcomes were in-hospital mortality and postoperative length of stay. Five process measures for surgical technique and secondary prevention were also analyzed. We described the changes in the overall performance and interhospital heterogeneity across the years. RESULTS: The in-hospital mortality declined from 0.9% in 2013 to 0.6 in 2018, with a risk-adjusted odds ratio of 0.66 (95% CI, 0.46-0.93; P<0.001). The standard mean difference for risk-standardized mortality rate between hospitals in the lowest and highest quartile narrowed from 1.63 in 2013 to 1.35 in 2018. The median (interquartile range) hospital-level rate of using arterial graft increased from 93.9% (86.0%-97.8%) to 94.6% (83.3%-99.2%), but the difference was not statistically significant. Meanwhile, the rate of free from blood transfusion increased from 17.0% (2.6%-32.0%) to 34.1% (8.8%-52.9%). The hospital-level rate of prescribing ß-blockers at discharge significantly increased from 82.8% (66.7%-90.3%) to 91.1% (82.1%-97.1%), statin from 75.8% (55.7%-88.9%) to 88.9% (75.0%-96.0%), and aspirin from 90.3% (83.9%-95.2%) to 95.3% (88.9%-98.1%). CONCLUSIONS: In the Chinese Cardiac Surgery Registry, there were notable improvements in the treatment process related to CABG and decline of in-hospital mortality with reduced interhospital heterogeneity.

Effect of a smartphone-based intervention on secondary prevention medication prescriptions after coronary artery bypass graft surgery: The MISSION-1 randomized controlled trial.

BACKGROUND: Studies found that patients who underwent coronary artery bypass grafting (CABG) often fail to receive optimal evidence-based secondary prevention medications. We evaluated the effectiveness of a smartphone-based quality improvement effort on improving the prescription of medical therapies. METHODS: In this cluster-randomized controlled trial, 60 hospitals were randomized to a control arm (n = 30) or to an intervention arm using smartphone-based multifaceted quality improvement interventions (n = 30). The primary outcome was the prescription of statin. The secondary outcomes were prescription of beta-blocker, angiotensin-converting enzyme inhibitor, or angiotensin receptor blocker (ACE inhibitor or ARB), and optimal medical therapy for eligible patients. RESULTS: Between June 1, 2015 and September 15, 2016, a total of 10,006 CABG patients were enrolled (5,653 in 26 intervention and 4,353 in 29 control hospitals, 5 hospitals withdrew). Statin prescribing rate was 87.8% in the intervention arm and 84.4% in the control arm. We saw no evidence of an effect of intervention on statin prescribing in the intention-to-treat analysis (odds ratio [OR], 1.31; 95% confidence interval (CI), 0.68-2.54; P = .43) or in key patient subsets. The prescription rates of ACE inhibitor or ARB and optimal medical therapy were comparable between study groups, while beta-blocker was more often prescribed in the intervention arm. Post hoc analysis demonstrated a greater increase in statin prescribing rate over time in the intervention arm. CONCLUSIONS: A smartphone-based quality improvement intervention compared with usual care did not increase statin prescribing for patients who received CABG. New studies focusing on the best practice of this technique may be warranted.

Involvement of DNA methylation in regulating the accumulation of the aroma compound indole in tea (Camellia sinensis) leaves during postharvest processing.

The manufacturing process of tea (Camellia sinensis), especially oolong tea, involves multiple postharvest stresses. These stresses can induce the formation and accumulation of many important aroma compounds, such as indole-a key floral aroma contributor of oolong tea. However, little is known about the regulation mechanisms of aroma compound formation, especially epigenetic regulation. DNA methylation is an important epigenetic modification. Changes in the DNA methylation levels of promoter sequences can regulate gene expression under stress conditions. In this study, the differences in DNA methylation levels and histone 3 lysine 9 dimethylation levels of indole key biosynthetic gene (tryptophan synthase ß-subunit 2, CsTSB2) were detected between untreated and continuous wounding treatment tea leaves. The results show that the DNA methylation levels affect the ability of the basic helix-loop-helix family transcription factor CsMYC2a to bind to the promoter of CsTSB2. Analyses of the transcript levels of DNA methyltransferases during oolong tea processing screened out candidate genes involved in the regulation of secondary metabolite product biosynthesis/accumulation. The results suggest that the domains rearranged methyltransferase 3, a DNA methyltransferase, is involved in the DNA methylation regulation of indole formation during the oolong tea manufacturing process. This is the first report on the involvement of DNA methylation in the regulation of aroma compound formation in tea leaves exposed to postharvest stresses.

Transformation of Salicylic Acid and Its Distribution in Tea Plants (Camellia sinensis) at the Tissue and Subcellular Levels.

Salicylic acid (SA) is a well-known immune-related hormone that has been well studied in model plants. However, less attention has been paid to the presence of SA and its derivatives in economic plants, such as tea plants (Camellia sinensis). This study showed that tea plants were rich in SA and responded differently to different pathogens. Feeding experiments in tea tissues further confirmed the transformation of SA into salicylic acid 2-O-ß-glucoside (SAG) and methyl salicylate. Nonaqueous fractionation techniques confirmed that SA and SAG were mostly distributed in the cytosol of tea leaves, consistent with distributions in other plant species. Furthermore, the stem epidermis contained more SA than the stem core both in C. sinensis cv. "Jinxuan" (small-leaf species) and "Yinghong No. 9" (large-leaf species). Compared with cv. "Yinghong No. 9", cv. "Jinxuan" contained more SAG in the stem epidermis, which might explain its lower incidence rate of wilt disease. This information will improve understanding of SA occurrence in tea plants and provide a basis for investigating the relationship between SA and disease resistance in tea plants.

Epigenetic Regulation of the Phytohormone Abscisic Acid Accumulation under Dehydration Stress during Postharvest Processing of Tea (Camellia sinensis).

The plant hormone abscisic acid (ABA) accumulates in tea leaves under dehydration stress during the withering process. However, the mechanism underlying ABA biosynthesis regulation remains largely unclear. In the present study, we found increased expression of ABA biosynthesis genes under dehydration stress during postharvest processing of tea. Furthermore, dehydration stress promoted ABA accumulation by increasing histone acetylation of ABA anabolism genes but by decreasing the levels of histone H3 lysine 9 dimethylation and DNA methylation of ABA biosynthesis genes. We screened candidate regulators of histone deacetylation and DNA methylation under dehydration stress. Taken together, our results indicate a role for epigenetic modifications during postharvest processing of tea.