Involvement of Phytohormone Responses of Rubber Leaves after Pestalotiopsis microspora Infection Revealed with Transcriptome Analysis

The circular leaf disease, caused by Pestalotiopsis spp., is a new primary foliar disease characterized by yellow-brown lesions that develop into dark-brown lesions on rubber leaves. This disease, named leaf fall disease, has recently led to significant economic losses in countries that produce natural rubber. However, molecular mechanisms that are involved in the interaction between P. microspora and rubber tree (Hevea brasiliensis) remain unclear. In this study, we conducted transcriptome analysis using RNA-seq of a susceptible rubber clone (GT1) after an inoculation with the mycelial plug of P. microspora. Among 84,443 rubber genes, the analysis revealed 3,799, 7,274, and 4,678 differentially expressed genes (DEGs) at 2, 4, and 6 days post-infection (dpi), respectively. Our Gene Ontology analysis of the DEGs detected the GO terms of the general hypersensitive response and systemic acquired resistance, which is known to be mediated by salicylic acid and hydrogen peroxide. We also detected the GO terms related to abscisic acid and ethylene responses. In addition, the detection of these two phytohormone transcriptional responses suggests the possible involvement of abscisic acid and/or ethylene in the process that led to the leaf fall symptom in susceptible rubber. Further, our promoter analysis to extract putative promoter elements responsive to the pathogen supported ethylene signaling activation by the pathogen infection. In addition, we extracted general Regulatory Element Groups that are position-dependent cis-regulatory elements, and established molecular markers for quantitative reverse transcription polymerase chain reaction. Our study provides genomic information and convenient tools for facilitating further exploration of Hevea-Pestalotiopsis interaction.