Molecular mechanism of CsERF9-mediated regulation of anthracnose resistance in tea plant

Tea plant (Camellia sinensis) is a globally important economic crop. Anthracnose, a major fungal disease caused by Colletotrichum camelliae, seriously threatens tea plant growth and leaf quality. Members of the ethylene response factor (ERF) family are key regulators in plant disease resistance signaling pathways. To identify critical genes involved in tea plant defense, this study screened differentially expressed genes based on previously obtained transcriptome data from tea plants inoculated with C. camelliae strain LS_19. From these, the candidate gene CsERF9 was selected for systematic investigation. Subcellular localization analysis confirmed that CsERF9 is localized in the nucleus, consistent with its predicted function as a transcription factor. Promoter cis-element analysis revealed that the CsERF9 promoter region is enriched with various defense- and hormone-response related elements, suggesting its potential involvement in pathogen-induced hormonal signaling. RT-qPCR results showed that CsERF9 expression was significantly induced upon C. camelliae infection and remained upregulated during later stages (24 h post-inoculation and beyond). Functional validation demonstrated that transient overexpression of CsERF9 in tea leaves significantly reduced resistance to anthracnose. Compared with the empty vector control, lesion areas in CsERF9-overexpressing leaves increased by 170.6%, 48.9%, and 40.7% at 24, 48, and 72 h post-inoculation, respectively, indicating that CsERF9 acts as a negative regulator of tea plant resistance to anthracnose. Further analysis revealed that CsERF9 overexpression significantly suppressed the expression of the salicylic acid (SA) pathway marker gene CsPR1, while upregulating the jasmonic acid/ethylene (JA/ET) pathway marker gene CsPR3. These findings suggest that CsERF9 may negatively regulate the tea plant’s immune response to C. camelliae by suppressing SA-mediated defenses and activating JA/ET signaling, thereby disrupting the balance between distinct disease-resistance pathways. This study provides novel insights into the molecular network of tea plant resistance to anthracnose and identifies CsERF9 as a potential candidate gene target for breeding disease-resistant tea cultivars.