Maize ZmBES1/BZR1-1 transcription factor negatively regulates drought tolerance.

Drought stress is a common abiotic factor and restricts plant growth and development. Exploring maize stress-related genes and their regulatory mechanisms is crucial for ensuring agricultural productivity and food security. The BRI1-EMS1 suppressor (BES1)/brassinazole-resistant 1 (BZR1) transcription factors (TFs) play important roles in plant growth, development, and stress response. However, maize ZmBES1/BZR1s are rarely reported. In the present study, the ZmBES1/BZR1-1 gene was cloned from maize B73 and functionally characterized in transgenic Arabidopsis and rice in drought stress response. The ZmBES1/BZR1-1 protein possessed a conserved bHLH domain characterized by BES1/BZR1 TFs, localized in the nucleus, and showed transcription activation activity. The expression of ZmBES1/BZR1-1 exhibited no tissue specificity but drought-inhibitory expression in maize. Under drought stress, overexpression of ZmBES1/BZR1-1 resulted in the enhancement of drought sensitivity of transgenic Arabidopsis and rice with a lower survival rate, reactive oxygen species (ROS) level and relative water content (RWC) and a higher stomatal aperture and relative electrolyte leakage (REL). The RNA-seq results showed that 56 differentially expressed genes (DEGs) were regulated by ZmBES1/BZR1-1 by binding to E-box elements in their promoters. The GO analysis showed that the DEGs were significantly annotated with response to oxidative stress and oxygen level. The study suggests that the ZmBES1/BZR1-1 gene negatively regulates drought stress, which provides insights into further underlying molecular mechanisms in the drought stress response mediated by BZR1/BES1s.