Functional divergence of growth-regulating factors CsGRF1 and CsGRF7 in Cucumis sativus defense against Podosphaera xanthii

As plant-specific transcription factors (TFs), growth-regulating factors (GRFs) play pivotal roles in regulating plant growth, development, and stress responses. Previous RNA-seq analysis revealed differential expression of CsGRF1 and CsGRF7 in cucumber under Podosphaera xanthii stress, suggesting their potential involvement in powdery mildew (PM) resistance. However, the functions and regulatory mechanisms of CsGRF1 and CsGRF7 in cucumber's defense remain unclear. In this study, we investigated the functional divergence of CsGRF1 and CsGRF7 in cucumber's PM defense. Subcellular localization, transcriptional activity, and protein interaction assays confirmed that both are typical members of the GRF TF family. Functional analyses demonstrated that CsGRF1 positively regulates cucumber resistance to P. xanthii, whereas CsGRF7 suppresses it. Further studies revealed that CsGRF1 enhances disease resistance by maintaining reactive oxygen species (ROS) homeostasis, while CsGRF7 negatively regulates lignin biosynthesis by directly interacting with CsODO1 (an MYB TF that inhibits PM resistance), thereby reducing defense responses. This study elucidates distinct regulatory roles of GRF family members in PM resistance and provides a theoretical foundation for improving cucumber disease resistance.