The growth and development of eukaryotic organisms is determined by the interactions between their genetic make-up and the environment. At the molecular level this translates into differential gene expression, giving rise to distinctly specialized cells, tissues, and/or organs. Regulation of gene expression or repression often entails modifying chromatin, a complex structure consisting of DNA wrapped around an octamer of histones (the nucleosome) as the basic repeating unit. Post-translational histone modifications (such as methylation and phosphorylation) play an important role in determining chromatin states associated with gene expression or repression. These covalent modifications can be propagated mitotically, resulting in heritable epigenetic states. However, relatively little is known about the role of histone methylation or phosphorylation in the regulation of euchromatic genes in photosynthetic eukaryotes. Even in metazoan and fungal systems, where the function of histone modifications in modulating chromatin has been examined much more extensively, there are still numerous unresolved and sometimes confusing observations. This project will focus on the molecular mechanisms responsible for, and the role of, methylation and phosphorylation of core histones in the transcriptional silencing of euchromatin in the green alga Chlamydomonas reinhardtii and the higher plant Arabidopsis thaliana. Preliminary findings suggest that monomethyl histone H3 lysine 4 (H3K4) appears to operate as a euchromatic silencing mark whereas di- and tri-methyl H3K4 correlate with transcriptionally active chromatin. The research will examine the molecular machinery(ies) responsible for gene silencing through H3K4 monomethylation. The project will also address the function of a novel serine/threonine protein kinase, which phosphorylates histones H3 and H2A, in the modulation of chromatin structure and gene repression. Orthologs of this protein appear to be limited to the plant lineage and their role in Arabidopsis development will also be tested. It is anticipated that the project will contribute to our understanding of both the molecular components involved in determining euchromatic states as well as the plant developmental processes controlled by these mechanisms.
The project is also expected to have practical implications for both agriculture and medicine. A better understanding of epigenetic gene silencing mechanisms may lead to improvements in transgenic technology as well as in therapy against certain diseases associated with epigenetic phenomena such as cancer. The mutant strains and vectors generated as part of this research will also be a valuable resource for the research community. In addition, the project will have an impact on human resource development through the direct training of undergraduate students, one graduate student, and one postdoctoral fellow. Students will learn research methodology via hands on experience, with the goal of fostering their interest in scientific discovery. The postdoctoral fellow and the graduate student will also contribute to the development and teaching of a Plant Biotechnology course. Lastly, characterization of chromatin modifying genes will also facilitate the annotation of novel genes in the nearly completed Chlamydomonas genome sequence.
