The splicing factor BRR2a functions as a repressor of stress-inducible genes

Inducible gene expression is generally thought to be activated when transcription factors bind to promoter cis-elements, thereby recruiting the general transcriptional machinery to initiate gene transcription. However, the mechanisms that repress inducible genes under non-inducing conditions remain poorly understood. In this study, we identified a novel mutant, shi6, which exhibits slow growth, a dwarf phenotype, and elevated expression of a luciferase (LUC) reporter gene driven by a salt-inducible promoter. The shi6 mutant also displayed increased sensitivity to abscisic acid (ABA), NaCl, and methyl jasmonate. Map-based cloning revealed that SHI6 encodes the RNA helicase BRR2a, a core component required for pre-mRNA splicing and essential for plant embryogenesis. As expected, SHI6/BRR2a was required for the proper splicing of stress-inducible genes. Unexpectedly, SHI6/BRR2a also exhibited transcriptional activation activity in both yeast and Arabidopsis, suggesting that it associates with the transcriptional machinery and participates in gene transcription. Together, our findings demonstrate that SHI6/BRR2a is a dual-function protein that plays essential roles in both pre-mRNA splicing and the repression of stress-inducible genes under non-inducing conditions.