Molecular analysis and expression profiling of blister blight defenserelated genes in tea

Fungal diseases are one of the biggest threats for plant growth, development and productivity. Exobasidium vexans is an obligate biotrophic fungal pathogen of tea that causes blister blight, a devastating disease resulting in significant crop losses. A study was carried out to do a comprehensive transcriptome profiling utilizing cDNA-AFLP and SSH along with qRT-PCR based expression profiling, with the objective of identification of blister blight inducible defense-related transcripts in tea, particularly in a resistant cultivar.This could potentially be utilized for development of molecular markers associated with resistance blister blight. Candidate transcripts were screened using cDNA-AFLF method, which are differentially expressed between a resistant and a susceptible cultivar under blister blight stress. Further, SSH libraries were constructed for identification of blister blight induced ESTs in the resistant cultivar. In silico analysis, functional annotation and characterization showed that E. vexans challenge rapidly modulates the expression of a large repertoire of genes associated with an array of biochemical processes, particularly defense. A high level of E. vexans- dependent induction was detected for most of the selected genes through qRT-PCRbased expression profiling of selected ESTs. This entire collection of blister blight induced ESTs includes genes involved not only in defense, but in metabolism, energy, transport, protein modification, cell wall fortification, oxidative stress response and signal transduction, which have either direct or indirect implications in conferring plant defense or resistance responses. A number of novel genes were also identified, which need to be investigated further for their probable roles in defense progression. The data provide potential candidates for improving resistance to blister blight either by marker assisted breeding or genetic engineering and sequence information for marker development (SNPs and SSRs), microarray construction, and genome annotation and the information accrued is expected to accelerate molecular characterization of genes of interest.