The CsBT1 Gene from Cucumber (Cucumis sativus L.) Negatively Regulates Salt and Drought Tolerance in Transgenic Arabidopsis Plants

BTB-TAZ (BT) proteins are plant-specific transcription factors that contain a BTB domain and a TAZ domain and play vital roles in various biological processes, growth regulation, and stress responses. In this study, we investigate the effect of overexpressing the cucumber CsBT1 gene in Arabidopsis thaliana on its tolerance to salt and drought. Quantitative analysis revealed significant downregulation of CsBT1 under salt and drought treatments, contrasting with its ABA-induced expression. The CsBT1 gene was introduced into Arabidopsis under the control of 35S promoter via floral dip transformation method. Two CsBT1-overexpressing transgenic Arabidopsis lines were used for stress treatment and phenotypic studies. The transgenic lines exhibited reduced germination, shorter root lengths, and accelerated leaf chlorosis under salt and drought treatments, in comparison to wild-type (WT) plants. Furthermore, overexpressed lines accumulated higher reactive oxygen species with lower superoxide dismutase (SOD) activity, correlating with increased electrolyte leakage and malondialdehyde (MDA) content. Notably, abscisic acid (ABA) treatment rescued the root growth inhibition in CsBT1-overexpressing transgenic Arabidopsis lines. Taken together, these results establish CsBT1 as a key negative regulator of salt and drought tolerance that functions through the ABA signaling pathway.