The RPD3L deacetylation complex is required for facultative heterochromatin repression in <i>Neurospora crassa</i>.

Abstract

Repression of facultative heterochromatin is essential for developmental processes in numerous organisms. Methylation of histone H3 lysine 27 (H3K27) by Polycomb repressive complex 2 is a prominent feature of facultative heterochromatin in both fungi and higher eukaryotes. Although this methylation is frequently associated with silencing, the detailed mechanism of repression remains incompletely understood. We utilized a forward genetics approach to identify genes required to maintain silencing at facultative heterochromatin genes in <i>Neurospora crassa</i> and identified three previously uncharacterized genes that are important for silencing: <i>sds3</i> (<i>NCU01599</i>), <i>rlp1</i> (<i>RPD3L protein 1</i>; <i>NCU09007</i>), and <i>rlp2</i> (<i>RPD3L protein 2</i>; <i>NCU02898</i>). We found that SDS3, RLP1, and RLP2 associate with <i>N. crassa</i> homologs of the <i>Saccharomyces cerevisiae</i> Rpd3L complex and are required for repression of a subset of H3K27-methylated genes. Deletion of these genes does not lead to loss of H3K27 methylation but increases acetylation of histone H3 lysine 14 at up-regulated genes, suggesting that RPD3L-driven deacetylation is a factor required for silencing of facultative heterochromatin in <i>N. crass</i>a, and perhaps in other organisms.