Suppression of CsDREB1B-1 promotes canker resistance via down-regulation of CsNCED1-1 expression and ABA biosynthesis in citrus

Citrus canker, resulting from Xanthomonas citri subsp. citri (Xcc) infection, is a significant problem in the global citrus industry. Stress signaling is regulated by several transcription factors (TFs) in the plant stress response, including dehydration-responsive element-binding (DREB) TFs. Previous studies have found that CsDREB1B-1 responds to Xcc infestation in citrus; however, its function remains unidentified. This study showed that following Xcc infection, CsDREB1B-1 expression was significantly increased in the susceptible Wanjincheng orange (Citrus sinensis Osbeck) cultivar. While its overexpression resulted in increased susceptibility, RNA interference silenced CsDREB1B-1 and induced higher resistance to citrus canker. Furthermore, utilizing the yeast one-hybrid (Y1H) experiment, dual-luciferase (LUC) reporter assay, and electrophoretic mobility shift assay (EMSA), CsDREB1B-1 was found to directly control the transcription of CsNCED1-1, a gene essential for ABA biosynthesis. Moreover, CsDREB1B-1 silenced plants displayed a substantial reduction in the abscisic acid (ABA) and a significant increase in salicylic acid (SA) levels, while the overexpression plants showed an opposite trend of change. The results showed that lowering CsDREB1B-1 expression caused less ABA build-up from CsNCED1-1 downregulation, which then decreased the inhibitory interaction between ABA and SA-mediated defensive responses, which improved resistance to citrus canker. The current work provides genetic resources, as well as mechanistic knowledge, that may help produce citrus canker-resistant varieties.