MdRAD5B regulates the chromatin accessibility of MdMYB14 under cold by associating with a transcription factor MdLSD1

RADIATION SENSITIVE 5B (MdRAD5B) has previously been identified as a chromatin remodeler involved in regulating the chromatin accessibility and H3K27me3 modification of genes. However, how RAD5B regulates the chromatin accessibility of target genes remains largely unclear. Here, we find that MdRAD5B positively regulates apple cold tolerance by modulating the expression of cold-responsive genes. Under cold stress, MdRAD5B regulates the expression of cold-responsive genes, including MdMYB14, through its chromatin remodeling function. Further study reveals that the transcription factor LESION SIMULATING DISEASE 1 (MdLSD1) recruits MdRAD5B and reduces the chromatin accessibility of MdMYB14. MdMYB14, a downstream target of MdLSD1 and a negative regulator of cold tolerance, binds to the promoter region of MdCBF3 and inhibits its expression. Additionally, we identified a natural variation, a non-synonymous mutation at position 1,780 of the RAD5B CDS (RAD5B^CDS1780), which affects apple cold tolerance by altering the ATPase activity of RAD5B. Taken together, our results unravel the underlying molecular mechanism by which MdRAD5B negatively regulates the chromatin accessibility of MdMYB14 through MdLSD1 in apple responses to cold.