PC-5p-1042181_5 Negatively Regulates Resistance to Tea Plant Diseases Caused by <i>Lasiodiplodia theobromae</i> Through Targeting <i>CsETR2</i> and Scavenging Reactive Oxygen Species

In recent years, diseases of tea plants (<i>Camellia sinensis</i>) caused by <i>Lasiodiplodia theobromae</i> have significantly impacted the quality and yield of tea leaves in China and India. However, the pathogenic mechanisms of <i>L. theobromae</i> in tea plants remain unclear. In this study, the relative expression levels of <i>ethylene receptor 2</i> (<i>ETR2</i>, historically referred to as <i>ethylene response 2</i>) mRNA was analyzed at different hours postinoculation at the first, second, and third leaves on the tea shoot inoculated with <i>L. theobromae</i> hyphae. The results revealed spatiotemporal differences in <i>CsETR2</i> expression, suggesting its involvement in disease resistance. Subcellular localization analysis indicated that CsETR2 was localized in the endoplasmic reticulum of leaf cells in <i>Nicotiana benthamiana</i>. Through transient overexpression, antisense oligonucleotide (AsODN) silencing in tea leaves, and transgenic <i>N. benthamiana</i> assays, it was confirmed that CsETR2 positively regulated resistance in <i>N. benthamiana</i>. 3,3'-Diaminobenzidine/nitroblue tetrazolium staining and quantitative analysis of reactive oxygen species (ROS) scavenger genes demonstrated that CsETR2 mediated disease resistance through an ROS-mediated mechanism. As a key component in ethylene (ET) signal transduction, the expression of <i>CsETR2</i> was positively correlated with genes in the ET transduction pathways under overexpression or silencing conditions. β-Glucuronidase and dual-luciferase assays revealed that PC-5p-1042181_5 inhibited <i>CsETR2</i> mRNA expression by targeting its mRNA, thereby reducing disease resistance. Further experiments with transient overexpression, AsODN silencing, and transgenic <i>N. benthamiana</i> validated the negative regulatory role of PC-5p-1042181_5. This study uncovered a novel disease resistance mechanism involving ROS-ET interference mediated by the PC-5p-1042181_5-<i>CsETR2</i> module, offering new insights for breeding disease-resistant tea cultivars.