| Vernalization is the phenomenon of flowering being promoted by long period of near-freezing temperatures (e.g., natural winter). In Arabidopsis, a flowering repressor gene, FLOWERING LOCUS C (FLC), is believed to be the main target of vernalization. Although several genes have been identified as either positive or negative FLC regulators, none of them is required for the vernalization mechanism.;In order to achieve a better understanding of vernalization at the molecular level, a genetic approach has been carried out to identify Arabidopsis genes that promote FLC expression. Seven genetic loci, designated VERNALIZATION INDEPENDENCE (VIP), were identified. All of the vip mutants show an early flowering phenotype and suppressed FLC mRNA expression. Besides flowering early, the vip mutants also show mild developmental pleiotropy, suggesting that VIPs play multiple roles in plant development.;Two of the VIP genes, VIP3 and VIP4, have been cloned from the presented dissertation. VIP3 encodes a protein composed of almost entirely WD repeats, suggesting a role in protein-protein interaction. VIP4 encodes a protein with sequence homology to a yeast protein Leo1p, a subunit of the yeast transcription complex named Paf1/RNA polymerase II complex (Paf1C). Later research of this laboratory revealed that the VIP2, VIP5 and VIP6 all encode proteins similar to the components of Paf1C. The sequence homology between these VIPs and Paf1C components suggests that some VIPs, if not all, could be subunits of a plant transcription complex that is similar to the yeast Paf1C.;A genetic approach and a biochemical approach were adopted to test the hypothesis that VIPs may present in a protein complex. My results showed that genetic combinations of vip4 mutation with mutations in the other six VIP genes did not give an enhanced mutant phenotype when compared with either of the parental single mutant. Furthermore, VIP3, VIP4 and VIP6 proteins were shown to physically interact with each other in vivo. Both results indicate that VIPs are components of a protein complex.;The outcomes of the presented study suggest that VIPs might represent a previously un-recognized transcriptional regulation mechanism in plants. |
