MaMYB4 Recruits Histone Deacetylase MaHDA2 and Modulates the Expression of ω-3 Fatty Acid Desaturase Genes during Cold Stress Response in Banana Fruit

Linoleic acid (LA; C18:2) and alpha-linolenic acid (ALA; C18:3) are two essential unsaturated fatty acids that play indispensable roles in maintaining membrane integrity in cold stress, and omega-3 fatty acid desaturases (FADs) are responsible for the transformation of LA into ALA. However, how this process is regulated at transcriptional and posttranscriptional levels remains largely unknown. In this study, an MYB transcription factor, MaMYB4, of a banana fruit was identified and found to target several omega-3 MaFADs, including MaFAD3-1, MaFAD3-3, MaFAD3-4 and MaFAD3-7, and repress their transcription. Intriguingly, the acetylation levels of histones H3 and H4 in the promoters of omega-3 MaFADs were elevated in response to cold stress, which was correlated with the enhancement in the transcription levels of omega-3 MaFADs and the ratio of ALA/LA. Moreover, a histone deacetylase MaHDA2 physically interacted with MaMYB4, thereby leading to the enhanced MaMYB4-mediated transcriptional repression of omega-3 MaFADs. Collectively, these data demonstrate that MaMYB4 might recruit MaHDA2 to repress the transcription of omega-3 MaFADs by affecting their acetylation levels, thus modulating fatty acid biosynthesis. Our findings provided new molecular insights into the regulatory mechanisms of fatty acid biosynthesis in cold stress in fruits.