Poster: Regulation of gene expression

Abs # 796: Investigation of the role of plant PAF1-related proteins in global transcription and histone methylation

Presenter:	Oh, Sookyung , ohsookyu@msu.edu
Authors	Oh, Sookyung  (A) (B)  Ludwig, Philip  (A) (C)  Zhang, Hua  (A) (D)  Yan, Ying  (A) (C)  van Nocker, Steven  (A) (E)
Affiliations:	(A): Michigan State Univeristy (B): Program in Plant Breeding and Genetics (C): Program in Cell and Molecular Biology (D): Program in Genetics (E): Program in Plant Breeding and Genetics, Cell and Molecular Biology and Genetics

In Arabidopsis thaliana, the promotion of flowering by extended exposure to cold temperatures, a phenomenon called vernalization, is mediated through epigenetic silencing of the MADS box gene FLC. We formerly described a class of mutant designated vernalization independence (vip) that show vernalization-independent early flowering and constitutive silencing of FLC. In addition to the flowering-time defect, these mutants exhibit developmental pleiotropy, suggesting that the respective VIP genes are important for normal expression of other regulatory genes as well. We cloned VIP5 and VIP6 and found that the encoded proteins are closely related to components of the yeast transcriptional regulator PAF1, which plays a key role in transcription by mediating the establishment and/or maintenance of specific chromatin modifications associated with gene activation. These include ubiquitylation of histone H2B by RAD6-BRE1, and methylation of the N-terminal tail of histone H3 at lysine-4 (H3K4) by the Trithorax-like histone methyltransferase Set1. Several other components of PAF1 have also been conserved in higher eukaryotes. However, the potential role of these proteins in transcription and the epigenetic maintenance of gene activity has not been studied. We carried out transcriptional profiling of vip mutants using the Affymetrix ' whole genome' genechip. We found that loss of function of the VIP5 or VIP6 genes resulted in the misregulation of a common and restricted subset of potential developmental regulators. We also investigated conservation of VIP5/VIP6 function through analysis of the effect of the vip5/vip6 mutations on H3K4 methylation both at the 'global' level, and within VIP5/VIP6 regulatory targets including FLC.