The MYB transcription factors directly mediate abscisic acid signals in response to abiotic stress

MYB transcription factors (TFs), regulated by abscisic acid (ABA), are pivotal regulators of plant growth, development, and responses to biotic and abiotic stresses. However, the specific subset of ABA-upregulated MYB factors whose expression declines upon ABA withdrawal remains poorly characterized. To identify such ABA-responsive MYB genes, we performed RNA-sequencing on ABA-treated wild-type Arabidopsis thaliana, specifically focusing on transcripts rapidly induced by ABA treatment and subsequently repressed following ABA removal. This approach identified three MYB TF genes, MYB19, MYB42, and MYB121, as direct targets of ABA signaling. Phenotypic characterization revealed that myb19, myb42, and myb121 mutants exhibited reduced sensitivity to ABA, as evidenced by impaired suppression of seed germination, cotyledon greening, and root growth. Furthermore, ABA-induced stomatal closure was attenuated in these mutants. We demonstrated that ABA-responsive element binding factors (ABFs) directly activate the transcription of MYB19, MYB42, and MYB121. Crucially, ABA failed to significantly induce the expression of these MYB genes in abfs mutants, establishing ABF-dependent ABA regulation. Additionally, myb19, myb42, and myb121 mutants displayed compromised tolerance to polyethylene glycol (PEG)-mediated osmotic stress and salt stress. Collectively, our results demonstrate that MYB19, MYB42, and MYB121 function as essential components of the ABA signaling pathway, mediating diverse physiological responses and abiotic stress tolerance, thereby highlighting their potential for applications in plant improvement.