A B-Box (BBX) Transcription Factor from Cucumber, CsCOL9 Positively Regulates Resistance of Host Plant to .

B-box (BBX) transcription factors play crucial roles in plant growth, development, and defense responses to biotic and abiotic stresses. In this study, we cloned a BBX transcription factor gene, from cucumber and analyzed its role in the plant's defense against the feeding of . is expressed throughout all developmental stages in cucumber, with the highest expression in the leaves. is induced by feeding, salicylic acid (SA), methyl jasmonate (MeJA), and hydrogen peroxide (HO). Cucumber plants with silence (TRV2-CsCOL9) and overexpression (1301-CsCOL9) were obtained and analyzed. After silencing, survival rates and host selectivity for increased; however, the expression levels of genes encoding enzymes (, , ), activities of superoxide dismutase (SOD) and peroxidase (POD), and content of HO in plants were all reduced. overexpression led to decreased survival rates and host selectivity for . Conversely, the expression levels of genes (, and ), activities of SOD and POD, and content of HO increased after overexpression in plants. Collectively, our results demonstrate positively regulates cucumber resistance to by activating reactive oxygen species bursts. This study lays a theoretical foundation for the application of in cucumber resistance breeding and green pest control of .