The OsMyb4 gene family: stress response and transcriptional auto-regulation mechanisms

The rice OsMyb4 gene, which encodes a Myb transcription factor (TF), improves the stress tolerance/resistance when expressed in both monocotyledonous and dicotyledonous transgenic plants. In this study, a phylogenetic analysis showed the existence of putative OsMyb4 homologues in monocot and dicot species. In particular, the analysis revealed that OsMyb4 belongs to a small rice gene subfamily conserved among monocots. The expression analyses of the OsMyb4-like genes in rice, wheat, and Arabidopsis indicated that these genes are involved in the response to dehydration, cold, and wounding. Moreover, the in silico analysis of the 5' upstream regions of the Osmyb4-like genes highlighted that the positions of some cis-elements involved in the stress response were conserved among the putative promoters, especially between OsMyb4 and its putative paralog Os02g41510. Finally, our transient expression assays in tobacco protoplasts demonstrated that OsMyb4 is able to repress the activity of both its own promoter and the Os02g41510 promoter by acting on the same binding site. A compensatory mechanism of auto-regulation is consistent with the well-known complexity of the OsMyb4-activated pathway, and this mechanism could regulate the transcription of other genes belonging to the family.