Proteomic analysis of the compatible interaction of wheat and powdery mildew (Blumeria graminis f. sp. tritici)

Combating powdery mildew: Advances in molecular interactions between Blumeria graminis f. sp. tritici and wheat

Wheat powdery mildew caused by a biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a widespread airborne disease which continues to threaten global wheat production. One of the most chemical-free and cost-effective approaches for the management of wheat powdery mildew is the exploitation of resistant cultivars. Accumulating evidence has reported that more than 100 powdery mildew resistance genes or alleles mapping to 63 different loci (Pm1-Pm68) have been identified from common wheat and its wild relatives, and only a few of them have been cloned so far. However, continuous emergence of new pathogen races with novel degrees of virulence renders wheat resistance genes ineffective. An essential breeding strategy for achieving more durable resistance is the pyramiding of resistance genes into a single genotype. The genetics of host-pathogen interactions integrated with temperature conditions and the interaction between resistance genes and their corresponding pathogen a virulence genes or other resistance genes within the wheat genome determine the expression of resistance genes. Considerable progress has been made in revealing Bgt pathogenesis mechanisms, identification of resistance genes and breeding of wheat powdery mildew resistant cultivars. A detailed understanding of the molecular interactions between wheat and Bgt will facilitate the development of novel and effective approaches for controlling powdery mildew. This review gives a succinct overview of the molecular basis of interactions between wheat and Bgt, and wheat defense mechanisms against Bgt infection. It will also unleash the unsung roles of epigenetic processes, autophagy and silicon in wheat resistance to Bgt.

Glutathione S-transferase interactions enhance wheat resistance to powdery mildew but not wheat stripe rust

Wheat stripe rust and powdery mildew are important worldwide diseases of wheat (Triticum aestivum). The wheat cultivar Xingmin318 (XM318) is resistant to both wheat stripe rust and powdery mildew, which are caused by Puccinia striiformis f. sp. tritici (Pst) and Blumeria graminis f. sp. tritici (Bgt), respectively. To explore the difference between wheat defense response against Pst and Bgt, quantitative proteomic analyses of XM318 inoculated with either Pst or Bgt were performed using tandem mass tags technology. A total of 741 proteins were identified as differentially accumulated proteins (DAPs). Bioinformatics analyses indicated that some functional categories, including antioxidant activity and immune system process, exhibited obvious differences between Pst and Bgt infections. Intriguingly, only 42 DAPs responded to both Pst and Bgt infections. Twelve DAPs were randomly selected for reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis, and the mRNA expression levels of 11 were consistent with their protein expression. Furthermore, gene silencing using the virus-induced gene silencing system indicated that glutathione S-transferase (TaGSTU6) has an important role in resistance to Bgt but not to Pst. TaGSTU6 interacted with the cystathionine beta-synthase (CBS) domain-containing protein (TaCBSX3) in both Pst and Bgt infections. Knockdown of TaCBSX3 expression only reduced wheat resistance to Bgt infection. Overexpression of TaGSTU6 and TaCBSX3 in Arabidopsis (Arabidopsis thaliana) promoted plant resistance to Pseudomonas syringae pv. Tomato DC3000. Our results indicate that TaGSTU6 interaction with TaCBSX3 only confers wheat resistance to Bgt, suggesting that wheat has different response mechanisms to Pst and Bgt stress.

Ammonium fertilization increases the susceptibility to fungal leaf and root pathogens in winter wheat

Nitrogen (N) fertilization is indispensable for high yields in agriculture due to its central role in plant growth and fitness. Different N forms affect plant defense against foliar pathogens and may alter soil-plant-microbe interactions. To date, however, the complex relationships between N forms and host defense are poorly understood. For this purpose, nitrate, ammonium, and cyanamide were compared in greenhouse pot trials with the aim to suppress two important fungal wheat pathogens Blumeria graminis f. sp. tritici (Bgt) and Gaeumannomyces graminis f. sp. tritici (Ggt). Wheat inoculated with the foliar pathogen Bgt was comparatively up to 80% less infested when fertilized with nitrate or cyanamide than with ammonium. Likewise, soil inoculation with the fungal pathogen Ggt revealed a 38% higher percentage of take-all infected roots in ammonium-fertilized plants. The bacterial rhizosphere microbiome was little affected by the N form, whereas the fungal community composition and structure were shaped by the different N fertilization, as revealed from metabarcoding data. Importantly, we observed a higher abundance of fungal pathogenic taxa in the ammonium-fertilized treatment compared to the other N treatments. Taken together, our findings demonstrated the critical role of fertilized N forms for host-pathogen interactions and wheat rhizosphere microbiome assemblage, which are relevant for plant fitness and performance.

Proteomics and Interspecies Interaction Analysis Revealed Abscisic Acid Signalling to Be the Primary Driver for Oil Palm's Response against Red Palm Weevil Infestation

The red palm weevil (RPW; Rhynchophorus ferrugineus Olivier (Coleoptera Curculionidae)) is an invasive insect pest that is difficult to manage due to its nature of infesting the host palm trees from within. A holistic, molecular-based approach to identify proteins that correlate with RPW infestation could give useful insights into the vital processes that are prevalent to the host's infestation response and identify the potential biomarkers for an early detection technique. Here, a shotgun proteomic analysis was performed on oil palm (Elaeis guineensis; OP) under untreated (control), wounding by drilling (wounded), and artificial larval infestation (infested) conditions at three different time points to characterise the RPW infestation response at three different stages. KEGG pathway enrichment analysis revealed many overlapping pathways between the control, wounded, and infested groups. Further analysis via literature searches narrowed down biologically relevant proteins into categories, which were photosynthesis, growth, and stress response. Overall, the patterns of protein expression suggested abscisic acid (ABA) hormone signalling to be the primary driver of insect herbivory response. Interspecies molecular docking analysis between RPW ligands and OP receptor proteins provided putative interactions that result in ABA signalling activation. Seven proteins were selected as candidate biomarkers for early infestation detection based on their relevance and association with ABA signalling. The MS data are available via ProteomeXchange with identifier PXD028986. This study provided a deeper insight into the mechanism of stress response in OP in order to develop a novel detection method or improve crop management.

TMT-based quantitative proteomic analysis of the effects of Pseudomonas syringae pv. tabaci (Pst) infection on photosynthetic function and the response of the MAPK signaling pathway in tobacco leaves

To reveal the mechanism of photosynthesis inhibition by infection and the response of the MAPK signaling pathway to pathogen infection, tobacco leaves were inoculated with Pseudomonas syringae pv. tabaci (Pst), and the effects of Pst infection on photosynthesis of tobacco leaves were studied by physiological and proteomic techniques, with a focus on MAPK signaling pathway related proteins. Pst infection was observed to lead to the degradation of chlorophyll (especially Chl b) in tobacco leaves and the down-regulation of light harvesting antenna proteins expression, thus limiting the light harvesting ability. The photosystem II and I (PSII and PSI) activities were also decreased, and Pst infection inhibited the utilization of light and CO2. Proteomic analyses showed that the number of differentially expressed proteins (DEPs) under Pst infection at 3 d were significantly higher than at 1 d, especially the number of down-regulated proteins. The KEGG enrichment of DEPs was mainly enriched in the energy metabolism processes such as photosynthesis antenna proteins and photosynthesis. The down-regulation of chlorophyll a-b binding protein, photosynthetic electron transport related proteins (e.g., PSII and PSI core proteins, the Cytb6/f complex, PC, Fd, FNR), ATP synthase subunits, and key enzymes in the Calvin cycle were the key changes associated with Pst infection that may inhibit tobacco photosynthesis. The effect of Pst infection on the PSII electron acceptor side was significantly greater than that on the PSII donor side. The main factor that decreased the photosynthetic ability of tobacco leaves with Pst infection at 1 d may be the inhibition of photochemical reactions leading to an insufficient supply of ATP, rather than decreased expression of enzymes involved in the Calvin cycle. At 1 d into Pst infection, the PSII regulated energy dissipation yield Y(NPQ) may play a role in preventing photosynthetic inhibition in tobacco leaves, but the long-term Pst infection significantly inhibited Y(NPQ) and the expression of PsbS proteins. Proteins involved in the MAPK signaling pathway were up-regulated, suggesting the MAPK signaling pathway was activated to respond to Pst infection. However, at the late stage of Pst infection (at 3 d), MAPK signaling pathway proteins were degraded, and the defense function of the MAPK signaling pathway in tobacco leaves was damaged.

Nitric oxide and hydrogen sulfide modulate the NADPH-generating enzymatic system in higher plants

Nitric oxide (NO) and hydrogen sulfide (H2S) are two key molecules in plant cells that participate, directly or indirectly, as regulators of protein functions through derived post-translational modifications, mainly tyrosine nitration, S-nitrosation, and persulfidation. These post-translational modifications allow the participation of both NO and H2S signal molecules in a wide range of cellular processes either physiological or under stressful circumstances. NADPH participates in cellular redox status and it is a key cofactor necessary for cell growth and development. It is involved in significant biochemical routes such as fatty acid, carotenoid and proline biosynthesis, and the shikimate pathway, as well as in cellular detoxification processes including the ascorbate-glutathione cycle, the NADPH-dependent thioredoxin reductase (NTR), or the superoxide-generating NADPH oxidase. Plant cells have diverse mechanisms to generate NADPH by a group of NADP-dependent oxidoreductases including ferredoxin-NADP reductase (FNR), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH), NADP-dependent malic enzyme (NADP-ME), NADP-dependent isocitrate dehydrogenase (NADP-ICDH), and both enzymes of the oxidative pentose phosphate pathway, designated as glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). These enzymes consist of different isozymes located in diverse subcellular compartments (chloroplasts, cytosol, mitochondria, and peroxisomes) which contribute to the NAPDH cellular pool. We provide a comprehensive overview of how post-translational modifications promoted by NO (tyrosine nitration and S-nitrosation), H2S (persulfidation), and glutathione (glutathionylation), affect the cellular redox status through regulation of the NADP-dependent dehydrogenases.

TMT-based quantitative proteomic analysis reveals defense mechanism of wheat against the crown rot pathogen Fusarium pseudograminearum

BACKGROUND

Fusarium crown rot is major disease in wheat. However, the wheat defense mechanisms against this disease remain poorly understood.

RESULTS

Using tandem mass tag (TMT) quantitative proteomics, we evaluated a disease-susceptible (UC1110) and a disease-tolerant (PI610750) wheat cultivar inoculated with Fusarium pseudograminearum WZ-8A. The morphological and physiological results showed that the average root diameter and malondialdehyde content in the roots of PI610750 decreased 3 days post-inoculation (dpi), while the average number of root tips increased. Root vigor was significantly increased in both cultivars, indicating that the morphological, physiological, and biochemical responses of the roots to disease differed between the two cultivars. TMT analysis showed that 366 differentially expressed proteins (DEPs) were identified by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment in the two comparison groups, UC1110_3dpi/UC1110_0dpi (163) and PI610750_3dpi/PI610750_0dpi (203). It may be concluded that phenylpropanoid biosynthesis (8), secondary metabolite biosynthesis (12), linolenic acid metabolites (5), glutathione metabolism (8), plant hormone signal transduction (3), MAPK signaling pathway-plant (4), and photosynthesis (12) contributed to the defense mechanisms in wheat. Protein-protein interaction network analysis showed that the DEPs interacted in both sugar metabolism and photosynthesis pathways. Sixteen genes were validated by real-time quantitative polymerase chain reaction and were found to be consistent with the proteomics data.

CONCLUSION

The results provided insight into the molecular mechanisms of the interaction between wheat and F. pseudograminearum.

Association Mapping and Development of Marker-Assisted Selection Tools for the Resistance to White Pine Blister Rust in the Alberta Limber Pine Populations

Since its introduction to North America in the early 1900s, white pine blister rust (WPBR) caused by the fungal pathogen Cronartium ribicola has resulted in substantial economic losses and ecological damage to native North American five-needle pine species. The high susceptibility and mortality of these species, including limber pine (Pinus flexilis), creates an urgent need for the development and deployment of resistant germplasm to support recovery of impacted populations. Extensive screening for genetic resistance to WPBR has been underway for decades in some species but has only started recently in limber pine using seed families collected from wild parental trees in the USA and Canada. This study was conducted to characterize Alberta limber pine seed families for WPBR resistance and to develop reliable molecular tools for marker-assisted selection (MAS). Open-pollinated seed families were evaluated for host reaction following controlled infection using C. ribicola basidiospores. Phenotypic segregation for presence/absence of stem symptoms was observed in four seed families. The segregation ratios of these families were consistent with expression of major gene resistance (MGR) controlled by a dominant R locus. Based on linkage disequilibrium (LD)-based association mapping used to detect single nucleotide polymorphism (SNP) markers associated with MGR against C. ribicola, MGR in these seed families appears to be controlled by Cr4 or other R genes in very close proximity to Cr4. These associated SNPs were located in genes involved in multiple molecular mechanisms potentially underlying limber pine MGR to C. ribicola, including NBS-LRR genes for recognition of C. ribicola effectors, signaling components, and a large set of defense-responsive genes with potential functions in plant effector-triggered immunity (ETI). Interactions of associated loci were identified for MGR selection in trees with complex genetic backgrounds. SNPs with tight Cr4-linkage were further converted to TaqMan assays to confirm their effectiveness as MAS tools. This work demonstrates the successful translation and deployment of molecular genetic knowledge into specific MAS tools that can be easily applied in a selection or breeding program to efficiently screen MGR against WPBR in Alberta limber pine populations.

Potential Role of Photosynthesis in the Regulation of Reactive Oxygen Species and Defence Responses to Blumeria graminis f. sp. tritici in Wheat

Photosynthesis is not only a primary generator of reactive oxygen species (ROS) but also a component of plant defence. To determine the relationships among photosynthesis, ROS, and defence responses to powdery mildew in wheat, we compared the responses of the Pm40-expressing wheat line L658 and its susceptible sister line L958 at 0, 6, 12, 24, 48, and 72 h post-inoculation (hpi) with powdery mildew via analyses of transcriptomes, cytology, antioxidant activities, photosynthesis, and chlorophyll fluorescence parameters. The results showed that H₂O₂ accumulation in L658 was significantly greater than that in L958 at 6 and 48 hpi, and the enzymes activity and transcripts expression of peroxidase and catalase were suppressed in L658 compared with L958. In addition, the inhibition of photosynthesis in L658 paralleled the global downregulation of photosynthesis-related genes. Furthermore, the expression of the salicylic acid-related genes non-expressor of pathogenesis related genes 1 (NPR1), pathogenesis-related 1 (PR1), and pathogenesis-related 5 (PR5) was upregulated, while the expression of jasmonic acid- and ethylene-related genes was inhibited in L658 compared with L958. In conclusion, the downregulation of photosynthesis-related genes likely led to a decline in photosynthesis, which may be combined with the inhibition of peroxidase (POD) and catalase (CAT) to generate two stages of H₂O₂ accumulation. The high level of H₂O_2, salicylic acid and PR1 and PR5 in L658 possible initiated the hypersensitive response.

Comparative Proteomic Analysis of Wheat Carrying Pm40 Response to Blumeria graminis f. sp. tritici Using Two-Dimensional Electrophoresis

Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is considered a major wheat leaf disease in the main wheat producing regions of the world. Although many resistant wheat cultivars to this disease have been developed, little is known about their resistance mechanisms. Pm40 is a broad, effective resistance gene against powdery mildew in wheat line L699. The aim of this study was to investigate the resistance proteins after Bgt inoculation in wheat lines L699, Neimai836, and Chuannong26. Neimai836 with Pm21 was used as the resistant control, and Chuannong26 without any effective Pm genes was the susceptible control. Proteins were extracted from wheat leaves sampled 2, 4, 8, 12, and 24 h after Bgt inoculation, separated by two-dimensional electrophoresis, and stained with Coomassie brilliant blue G-250. The results showed that different proteins were upregulated and downregulated in three wheat cultivars at different time points. For the wheat cultivar L699, a total of 62 proteins were upregulated and 71 proteins were downregulated after Bgt inoculation. Among these, 46 upregulated proteins were identified by mass spectrometry analysis using the NCBI nr database of Triticum. The identified proteins were predicted to be associated with the defense response, photosynthesis, signal transduction, carbohydrate metabolism, energy pathway, protein turnover, and cell structure functions. It is inferred that the proteins are not only involved in defense response, but also other physiological and cellular processes to confer wheat resistance against Bgt. Therefore, the resistance products potentially mediate the immune response and coordinate other physiological and cellular processes during the resistance response to Bgt. The lipoxygenase, glucan exohydrolase, glucose adenylyltransferasesmall, phosphoribulokinase, and phosphoglucomutase are first reported to be involved in the interactions of wheat-Bgt at early stage. The further study of these proteins will deepen our understanding of their detailed functions and potentially develop more efficient disease control strategies.

Alterations in plant sugar metabolism: signatory of pathogen attack

This review summarizes the current understanding, future challenges and ongoing quest on sugar metabolic alterations that influence the outcome of plant-pathogen interactions. Intricate cellular and molecular events occur during plant-pathogen interactions. They cause major metabolic perturbations in the host and alterations in sugar metabolism play a pivotal role in governing the outcome of various kinds of plant-pathogen interactions. Sugar metabolizing enzymes and transporters of both host and pathogen origin get differentially regulated during the interactions. Both plant and pathogen compete for utilizing the host sugar metabolic machinery and in turn promote resistant or susceptible responses. However, the kind of sugar metabolism alteration that is beneficial for the host or pathogen is yet to be properly understood. Recently developed tools and methodologies are facilitating research to understand the intricate dynamics of sugar metabolism during the interactions. The present review elaborates current understanding, future challenges and ongoing quest on sugar metabolism, mobilization and regulation during various plant-pathogen interactions.

Comparative proteomic analysis of cucumber powdery mildew resistance between a single-segment substitution line and its recurrent parent

Powdery mildew (PM) is considered a major cause of yield losses and reduced quality in cucumber worldwide, but the molecular basis of PM resistance remains poorly understood. A segment substitution line, namely, SSL508-28, was developed with dominant PM resistance in the genetic background of PM-susceptible cucumber inbred line D8. The substituted segment contains 860 genes. An iTRAQ-based comparative proteomic technology was used to map the proteomes of PM-inoculated and untreated (control) D8 and SSL508-28. The number of differentially regulated proteins (DRPs) in SSL508-28 was almost three times higher than that in D8. Fourteen DRPs were located in the substituted segment interval. Comparative gene expression analysis revealed that nodulin-related protein 1 (NRP1) may be a good candidate for PM resistance. Gene Ontology enrichment analysis showed that DRPs functioning in tetrapyrrole biosynthetic process, sulfur metabolic process and cell redox homeostasis were specifically enriched in the resistant line SSL508-28. DRPs categorized in the KEGG term photosynthesis increased in both lines upon PM infection, suggesting that the strategies used by cucumber may be different from those used by other crops to react to PM attacks at the initial stage. The measurement of hydrogen peroxide and superoxide anion production and net photosynthetic rate were consistent with the changes in protein abundance, suggesting that the proteomic results were reliable. There was a poor correlation between DRPs measured by iTRAQ and the corresponding gene expression changes measured by RNA-seq with the same experimental design. Taken together, these findings improve the understanding of the molecular mechanisms underlying the response of cucumber to PM infection.

Transcriptome profiling of pumpkin (Cucurbita moschata Duch.) leaves infected with powdery mildew

Cucurbit powdery mildew (PM) is one of the most severe fungal diseases, but the molecular mechanisms underlying PM resistance remain largely unknown, especially in pumpkin (Cucurbita moschata Duch.). The goal of this study was to identify gene expression differences in PM-treated plants (harvested at 24 h and 48 h after inoculation) and untreated (control) plants of inbred line “112–2” using RNA sequencing (RNA-Seq). The inbred line “112–2” has been purified over 8 consecutive generations of self-pollination and shows high resistance to PM. More than 7600 transcripts were examined in pumpkin leaves, and 3129 and 3080 differentially expressed genes (DEGs) were identified in inbred line “112–2” at 24 and 48 hours post inoculation (hpi), respectively. Based on the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway database and GO (Gene Ontology) database, a complex regulatory network for PM resistance that may involve hormone signal transduction pathways, transcription factors and defense responses was revealed at the transcription level. In addition, the expression profiles of 16 selected genes were analyzed using quantitative RT-PCR. Among these genes, the transcript levels of 6 DEGs, including bHLH87 (Basic Helix-loop-helix transcription factor), ERF014 (Ethylene response factor), WRKY21 (WRKY domain), HSF (heat stress transcription factor A), MLO3 (Mildew Locus O), and SGT1 (Suppressor of G-Two Allele of Skp1), in PM-resistant “112–2” were found to be significantly up- or down-regulated both before 9 hpi and at 24 hpi or 48 hpi; this behavior differed from that observed in the PM-susceptible material (cultivar “Jiujiangjiaoding”). The transcriptome data provide novel insights into the response of Cucurbita moschata to PM stress and are expected to be highly useful for dissecting PM defense mechanisms in this major vegetable and for improving pumpkin breeding with enhanced resistance to PM.

Infection of Powdery Mildew Reduces the Fitness of Grain Aphids (Sitobion avenae) Through Restricted Nutrition and Induced Defense Response in Wheat

In natural ecological systems, plants are often simultaneously attacked by both insects and pathogens, which can affect each other's performance and the interactions can be extended to higher trophic levels, such as parasitoids. The English grain aphid (Sitobion avenae) and powdery mildew (Blumeria graminis f. sp. tritici) are two common antagonists that pose a serious threat to wheat production. Numerous studies have investigated the effect of a single factor (insect or pathogen) on wheat production. However, investigation on the interactions among insect pests, pathogens, and parasitoids within the wheat crop system are rare. Furthermore, the influence of the fungicide, propiconazole, has been found to imitate the natural ecosystem. Therefore, this study investigated the effects of B. graminis on the biological performance of grain aphids and the orientation behavior of its endoparasitic wasp Aphidius gifuensis in the wheat system. Our findings indicated that B. graminis infection suppressed the feeding behavior, adult and nymph weight, and fecundity and prolonged the developmental time of S. avenae. We found that wheat host plants had decreased proportions of essential amino acids and higher content of sucrose following aggravated B. graminis infection. The contents of Pro and Gln increased in the wheat plant tissues after B. graminis infection. In addition, B. graminis infection elicited immune responses in wheat: increase in the expression of defense genes, content of total phenolic compounds, and activity of three related antioxidant enzymes. Moreover, co-infection of B. graminis and S. avenae increased the attraction to A. gifuensis compare to that after infestation with aphids alone. In conclusion, our results indicated that B. graminis infection adversely affected the performance of S. avenae in wheat through restricted nutrition and induced defense response. Furthermore, the preference of parasitoids in such an interactive environment might provide an important basis for pest management control.

Transcriptional analysis and histochemistry reveal that hypersensitive cell death and H2O2 have crucial roles in the resistance of tea plant (Camellia sinensis (L.) O. Kuntze) to anthracnose

Anthracnose causes severe losses of tea production in China. Although genes and biological processes involved in anthracnose resistance have been reported in other plants, the molecular response to anthracnose in tea plant is unknown. We used the susceptible tea cultivar Longjing 43 and the resistant cultivar Zhongcha 108 as materials and compared transcriptome changes in the leaves of both cultivars following Colletotrichum fructicola inoculation. In all, 9015 and 8624 genes were differentially expressed between the resistant and susceptible cultivars and their controls (0 h), respectively. In both cultivars, the differentially expressed genes (DEGs) were enriched in 215 pathways, including responses to sugar metabolism, phytohormones, reactive oxygen species (ROS), biotic stimuli and signalling, transmembrane transporter activity, protease activity and signalling receptor activity, but DEG expression levels were higher in Zhongcha 108 than in Longjing 43. Moreover, functional enrichment analysis of the DEGs showed that hydrogen peroxide (H₂O₂) metabolism, cell death, secondary metabolism, and carbohydrate metabolism are involved in the defence of Zhongcha 108, and 88 key genes were identified. Protein-protein interaction (PPI) network demonstrated that putative mitogen-activated protein kinase (MAPK) cascades are activated by resistance (R) genes and mediate downstream defence responses. Histochemical analysis subsequently validated the strong hypersensitive response (HR) and H₂O₂ accumulation that occurred around the hyphal infection sites in Zhongcha 108. Overall, our results indicate that the HR and H₂O₂ are critical mechanisms in tea plant defence against anthracnose and may be activated by R genes via MAPK cascades.