Abstract
To unravel the molecular mechanism of defense against blister blight (BB) disease caused by an obligate biotrophic fungus, Exobasidium vexans, transcriptome of BB interaction with resistance and susceptible tea genotypes was analysed through RNA-seq using Illumina GAIIx at four different stages during ~20-day disease cycle. Approximately 69 million high quality reads were assembled de novo, yielding 37,790 unique transcripts with more than 55% being functionally annotated. Differentially expressed, 149 defense related transcripts/genes, namely defense related enzymes, resistance genes, multidrug resistant transporters, transcription factors, retrotransposons, metacaspases and chaperons were observed in RG, suggesting their role in defending against BB. Being present in the major hub, putative master regulators among these candidates were identified from predetermined protein-protein interaction network of Arabidopsis thaliana. Further, confirmation of abundant expression of well-known RPM1, RPS2 and RPP13 in quantitative Real Time PCR indicates salicylic acid and jasmonic acid, possibly induce synthesis of antimicrobial compounds, required to overcome the virulence of E. vexans. Compendiously, the current study provides a comprehensive gene expression and insights into the molecular mechanism of tea defense against BB to serve as a resource for unravelling the possible regulatory mechanism of immunity against various biotic stresses in tea and other crops.
Highlights
Tea (Camellia sinensis (L) Kuntze) is one of the most popular non-alcoholic beverage crops, globally
WRKY, NAM transcription factors, LTR retrotransposons, chaperons and metacaspases are among the major defense regulators[20,24], wherein, WRKY and NAM transcription factors play significant role in large scale transcriptional reprogramming by binding to promoter elements of defense related genes and regulating their expression during plant immunity[25,26,27]
Considering the 20-day lifespan of E. vexans[8], four successive stages were categorized as exobasidiospore inoculation or landing of exobasidiospores on the upper surface of leaves [24 hrs post inoculation (PI), Stage[1] (S1)]; penetration/germination of spores inside the host tissue [7th day PI; Stage[2] (S2)], haustoria and mycelial development [14th day PI; Stage[3] (S3)] and sporulation of exobasidiospore [20th day PI; Stage 4 (S4)] (Fig. 1A)
Summary
Tea (Camellia sinensis (L) Kuntze) is one of the most popular non-alcoholic beverage crops, globally. Blister Blight (BB) disease caused by a basidiomycete obligate biotrophic pathogen Exobasidium vexans Massee, is amongst the most serious leaf diseases, significantly affecting commercial production in major tea producing countries, including India, Indonesia, Sri Lanka and Japan. This pathogen mainly attacks young succulent, harvestable tender leaves that cause more than 40% total yield loss[10], and affects the tea quality significantly by reducing total phenols and catechin content[11,12]. Well understood immune system of Arabidopsis and other crop plants suggests that biotrophic pathogens after entering through stomata proliferate in intercellular spaces and obtain nourishment through specialized haustoria. Comprehensive efforts of the current study jointly with conventional breeding techniques would accelerate genetic improvement of tea and other perennial crops
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