Seminars

Chromatin plays a pivotal role in regulation of eukaryotic genome function such as DNA replication and transcription in addition to its primary function in genome compaction. One of the major mechanisms of transcriptional repression is chromatin modification by the polycomb repressive complex 2 (PRC2), which deposits trimethyl mark onto lysine 27 of histone H3 (H3K27me3). While PRC2 targets developmental genes to maintain cellular identity, it also participates in mammalian X chromosome inactivation. Although functional diversity of PRC2 are well understood in several metazoans, less is known about diversity of PRC2 function in plants and almost nothing is known about how PRC2 function evolved during land plant evolution because it has been studied in a small number of flowering plant model species. To address these questions, we investigated PRC2 function in several extant species in Archaeplastida lineage. we discovered that PRC2 silences not only genes but also transposable elements (TEs) in a bryophyte Marchantia polymorpha and in a red alga Cyanidioschyzon merolae. Furthermore, we recently reported a unique form of genomic imprinting during embryogenesis in Marchantia polymorpha in which all paternally derived chromosomes are entirely silenced by embryo specific PRC2 subunits. Particularly, we discovered that the male and female pronucleus stay unfused for 3 days after fertilization and the male pronucleus specifically gets silenced via H3K27me3 deposition during this period. Based on these results, I would like to discuss how PRC2 function evolved during land plant diversification.