Genome-wide analysis of the 1R-MYB family in Syntrichia caninervis reveals ScMYB24 as a negative regulator of abiotic stress tolerance

Syntrichia caninervis, an extremotolerant desert moss, serves as an ideal model for studying abiotic stress tolerance mechanisms. The 1R-MYB transcription factors (TFs) are crucial in various biological processes and stress responses, yet their roles in S. caninervis remain poorly understood. Here, we performed a genome-wide identification of 39 1R-MYB TFs in S. caninervis and analyzed their phylogenetic relationships, promoter cis-elements, conserved domains, motif compositions, gene structures, collinearity, and expression patterns. ScMYB24, which was significantly downregulated under both salt and drought stresses, was selected for further functional characterization. ScMYB24 was confirmed as a nuclear-localized protein with transcriptional activation activity at its N-terminus. Dual-luciferase reporter assays demonstrated that ScMYB24 significantly suppressed the promoter activities of the key antioxidant genes ScCATβ1 and ScFSOD2. Consequently, overexpression of ScMYB24 in Arabidopsis thaliana and S. caninervis led to increased reactive oxygen species (ROS) accumulation, reduced expression of antioxidant enzymes, and diminished tolerance to salt and drought stresses. In contrast, ScMYB24-RNAi lines in S. caninervis exhibited lower ROS levels and enhanced stress resistance. Our study provides a comprehensive analysis of the Sc1R-MYB family and highlights that ScMYB24 negatively regulates salt and drought stress responses by repressing the transcription of critical antioxidant defense genes in S. caninervis.