Single-nucleus methylcytosine and transcriptome sequencing in pollen reveals antagonism between MBD5/6 and MBD7 in transcriptional regulation [RNA-seq]
MBD5, MBD6, and MBD7 are CG-specific methyl-readers with opposite functions: MBD5 and MBD6 (MBD5/6) redundantly repress methylated loci in pollen vegetative nuclei (VN), while MBD7 prevents transgene silencing, possibly by promoting DNA demethylation. Here we show that transcriptional derepression in mbd5/6 pollen is rescued by loss of MBD7, suggesting that MBD5/6 counteract MBD7 activity. By simultaneously profiling DNA methylation and gene expression in single pollen nuclei, we found that CG methylation is lost at MBD5/6 targets specifically in the early post-mitotic VN of mbd5/6. This loss precedes mbd5/6 transcriptional derepression and is largely restored in mbd5/6/7 triple mutants. Altering MBD6 to recruit the MBD7 complex instead of its normal interactors caused demethylation and upregulation of MBD5/6 targets, turning MBD6 from a repressor into an activator. We propose that in VN, where chromatin is decondensed, MBD5/6 are required to protect accessible DNA from demethylation and derepression by the MBD7 complex. Overall design: For libraries 1 and 2, to investigate the rescue of the mbd5/6 gene/TE derepression phenotype by mbd7 in pollen. For library 3, to test the effect of swapping the stkyC domain of MBD6 with the one of MBD7 on gene/TE expression in pollen.