The Pp CMT chromomethylase affects cell growth and interacts with the homolog of LIKE HETEROCHROMATIN PROTEIN  1 in the moss Physcomitrella patens

• Published in: The Plant journal : for cell and molecular biology 2014-02, Vol.77 (4), p.589-603
• Main Authors: Dangwal, Meenakshi, Kapoor, Sanjay, Kapoor, Meenu
• Format: Article
• Language: English
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12406

Chromomethylases ( CMT s) are plant‐specific cytosine DNA methyltransferases that are involved in maintenance of CpNpG methylation. In seed plants, histone methylation and interaction of CMT with LIKE HETEROCHROMATIN PROTEIN  1 ( LHP 1) is essential for recruitment of CMT to target sites. LHP 1 has been characterized as a putative component of the POLYCOMB REPRESSIVE COMPLEX 1 ( PRC 1) in plants, and functions downstream of PRC 2 to maintain genes in repressed state for orchestrated development. In the present study, we show that targeted disruption of Pp CMT results in an approximately 50% reduction in global cytosine methylation levels. This affects growth of apical cells, predominantly growth of side branch initials emerging from chloronema cells. In some places, these cells develop thick walls with plasmolyzed cellular contents. Transcript accumulation patterns of genes involved in apical cell extension and metabolism of hemicelluloses, such as xyloglucans, in the primary cell walls decreased many fold in ppcmt mutant lines, as determined by real‐time PCR . Using yeast two‐hybrid method and bimolecular fluorescence complementation assay, we show that Pp CMT and Pp LHP 1 interact through their chromo domains, while Pp LHP 1 homodimerizes through its chromo shadow domain. The results presented in this study provide insight into the role of the single chromomethylase, Pp CMT , in proliferation of protonema filaments, and shed light on the evolutionary conservation of proteins interacting with these methylases in the early land plant, Physcomitrella patens .