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

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