Involvement of phytohormone responses of rubber leaves after infection of Pestalotiopsis microspora revealed by transcriptome analysis
The circular leaf disease, caused by Pestalotiopsis spp., is a new primary foliar disease characterized by yellow-brown spots that develop into dark brown spots on rubber leaves. This disease, called leaf fall disease, has recently caused significant economic losses in countries that produce natural rubber. However, the molecular mechanisms involved in the interaction between P. microspora and H. brasiliensis are not well understood. In this study, we carried out transcriptome analysis by RNA-Seq of a susceptible rubber clone (GT-1) after inoculation with the mycelial plug of P. microspora. The analysis brought us to identify 3,799, 7,274, and 4,678 differentially expressed genes (DEGs) at 2, 4, and 6 days post infection (dpi), respectively. In addition to general hypersensitive response (HR) and systemic acquired response (SAR) mediated by salicylic acid and hydrogen peroxide, our Gene Ontology (GO) analysis of the detected DEGs revealed abscisic acid and ethylene responses. Detection of these two phytohormone responses suggests possible involvement of abscisic acid and/or ethylene in the process to lead the leaf fall in susceptible rubbers. Activation of the ethylene signaling by the pathogen infection was also supported by our promoter analysis, which detected GCC box in the putative cis-elements for the response to P. microspora infection. Regarding the down-regulated genes, GO analyses showed suppression of photosynthesis across the infection time points. In addition to global understanding of the transcriptional response of rubber to the pathogen, we extracted general Regulatory Element Group (REG) that are position-dependent cis-regulatory elements and covers half of the elements in a genome, and also established molecular markers for qRT-PCR. Our study provides genomic information and convenient tools for facilitating further exploration of Hevea-Pestalotiopsis interaction Overall design: RNA-Seq profilling of GT1 mature leaf under Pestalotiopsis microspora infection and mock condition