Genome-wide AP2/ERF analysis identifies HmaERF87 as a positive regulator of Hydrangea macrophylla leaf spot resistance.

A total of 164 APETALA2/ethylene-responsive factor (AP2/ERF) genes were identified in Hydrangea macrophylla, and HmaERF87 positively contributes to leaf spot resistance. The APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor family plays important roles in plant stress responses, but its contribution to disease resistance in Hydrangea macrophylla (hydrangea) remains poorly understood. In this study, 164 AP2/ERF genes were identified in the H. macrophylla genome and classified into APETALA2 (AP2), ethylene-responsive factor (ERF), dehydration-responsive element-binding (DREB), and related to ABI3/VP1 (RAV) subfamilies. Their chromosomal distribution, conserved motifs, gene structures, and duplication patterns were analyzed. A total of 46 pathogen-responsive H. macrophylla AP2/ERF (HmaERF) genes were identified from the RNA sequencing (RNA-seq) dataset of resistant and susceptible cultivar leaves collected before and after Corynespora cassiicola inoculation. Promoter analysis revealed that the HmaERF genes with upregulated expression post-C. cassiicola infection showed a higher frequency and copy number of jasmonate-responsive cis-regulatory elements, suggesting their possible involvement in hormone-mediated defense responses. Three infection-induced candidate genes, including HmaERF56, HmaERF87, and HmaERF129, were selected for functional validation using virus-induced gene silencing (VIGS) in hydrangea leaf discs. Silencing of HmaERF87 expression via VIGS significantly increased lesion development after C. cassiicola inoculation, whereas the transient overexpression of HmaERF87 reduced the area of leaf disc lesions. Subcellular localization showed that the HmaERF87 protein was localized in the nucleus, and yeast assays indicated that its transcriptional activation activity was mainly associated with the C-terminal region of the protein. These results support a role for HmaERF87 as a positive regulator of H. macrophylla resistance to leaf spot disease and provide a candidate gene for further studies of disease resistance in hydrangea.