Integrated transcriptome sequencing and iTRAQ quantitative proteomics analysis reveal the roles of PpJAZ1 and PpMYC2-2 in sand pear black spot disease resistance

Abstract

Pear black spot disease (BSD), caused by the pathogen Alternaria alternata, poses a significant threat to pear trees. In this study, we investigated the defense mechanisms of sand pear (Pyrus pyrifolia) against BSD using iTRAQ and transcriptome analysis. Proteome sequencing and iTRAQ-UPLC MS/MS identified 6487 reliable proteins, including 6230 quantifiable ones. Further analysis revealed 237 differential proteins following inoculation with the H strain of A. alternata. Among these, 20 were common to both 'Jinjing' pear and the susceptible 'Hongfen' pear, while 138 were specific to 'Jinjing' and 79 were specific to 'Hongfen'. Gene Ontology and KEGG analysis implicated these proteins in processes like "plastid", "ion binding", "ribosome", and "amino sugar and nucleotide sugar metabolism". We further identified 100 common genes from the proteome and transcriptome data, with 69% showing consistent expression patterns. Among these, we discovered a candidate gene, Pbr037418, which shares a close phylogenetic relationship with Arabidopsis AtJAZ1 and was designated PpJAZ1. We confirmed that PpJAZ1 is localized in the nucleus and interacts with PpMYC2-2 in the defense response. Notably, expression levels of PpJAZ1 and PpMYC2-2 were higher in resistant 'Jinjing' pear compared to susceptible 'Hongfen' pear after pathogen inoculation. Following H strain inoculation, sand pear leaves with silenced PpJAZ1 exhibited disease spots and showed reduced expression of PpJAZ1 and PpMYC2-2 compared to control leaves. This study deepens our understanding of BSD resistance mechanisms and provides insights into proteomic and transcriptomic changes in sand pear during pathogen infection, and thus will facilitate future research on resistance gene discovery and functional studies in sand pear.