Salinity stress induces epigenetic alterations to the promoter of MsMYB4 encoding a salt-induced MYB transcription factor

The transcriptomic response of plants to salinity stress is regulated in part by epigenetic alterations to gene promoter sequences. The transcription factor MsMYB4 is an important component of the response of alfalfa to salinity stress, but the involvement of epialleles of its encoding gene has not as yet been explored. Here, the MsMYB4 promoter was isolated using a genome walking approach in order to perform a deletion analysis to identify the region harboring the elements required for its stress inducibility. The analysis showed that these reside in the sequence lying between 739 and 336 nt up stream of the MsMYB4 translation start codon. The methylation status of the sequence around the MsMYB4 translation start site was altered by the imposition of salinity stress. The activation of MsMYB4 was associated with an increased level of histone H3K4 trimethylation and H3K9 acetylation in specific regions of the promoter sequence. Our results suggest a critical role for MsMYB4's activation by DNA methylation and/or histone modifications in response to salinity stress in alfalfa.