SbWRKY55 Regulates Sorghum Response to Saline Environment by Its Dual Role in Abscisic Acid Signaling

SbWRKY55 functions as a key component of the ABA-mediated signaling pathway; transgenic sorghum regulates plant responses to saline environments and will help save arable land and ensure food security. Salt tolerance in plants is triggered by various environmental stress factors and endogenous hormonal signals. Numerous studies have shown that WRKY transcription factors are involved in regulating plant salt tolerance. However, the underlying mechanism for WRKY transcription factors regulated salt stress response and signal transduction pathways remains largely unknown. In this study, the SbWRKY55 transcription factor was found to be the key component for reduced levels of salt and abscisic acid in SbWRKY55 overexpression significantly reduced salt tolerance in sorghum and Arabidopsis. Mutation of the homologous gene AtWRKY55 in A. thaliana significantly enhanced salt tolerance, and SbWRKY55 supplementation in the mutants restored salt tolerance. In the transgenic sorghum with SbWRKY55 overexpression, the expression levels of genes involved in the abscisic acid (ABA) pathway were altered, and the endogenous ABA content decreased. Yeast one-hybrid assays and dual-luciferase reporter assay showed that SbWRKY55 binds directly to the promoter of SbBGLU22 and inhibits its expression level. In addition, both in vivo and in vitro biochemical analyses showed that SbWRKY55 interacts with the FYVE zinc finger protein SbFYVE1, blocking the ABA signaling pathway. This could be an important feedback regulatory pathway to balance the SbWRKY55-mediated salt stress response. In summary, the results of this study provide convincing evidence that SbWRKY55 functions as a key component in the ABA-mediated signaling pathway, highlighting the dual role of SbWRKY55 in ABA signaling. This study also showed that SbWRKY55 could negatively regulate salt tolerance in sorghum.