A switch from TE-like heterochromatin to euchromatin underlies activation of protein storage genes in maize endosperm

Abstract

Unlike the stable transcription of plant genes with CG gene body methylation alone, genes with methylation in TE-like CHG and CG contexts are poorly transcribed and often missanotated. In contrast, here we describe a set of TE-like methylated genes that are maternally demethylated and expressed toward the extreme high end of the spectrum in endosperm. They are enriched for short, secreted proteins, and about a third encode zeins, the major seed storage proteins of maize. Consistent with their dynamic expression in endosperm, they acquire either activating or repressive gene regulatory modifications when demethylated but are heterochromatic when methylated in other tissues. The majority are expressed both maternally and paternally, but a subset whose methylation/demethylation extends upstream of gene bodies into promoters are strongly imprinted. These and other data indicate that TE-like methylation and associated heterochromatin can be a signature of broad silencing but exceptionally high and specific gene expression in either pollen or endosperm.