Research Spotlight

Dr. Richard M. Amasino

Department of Biochemistry
University of Wisconsin-Madison

Madison, WI 53706-1544

Research interests: Our research is focused on the transition to flowering; i.e., we study how the “decision” of a shoot meristem to form either flowers or leaves controlled. In Arabidopsis thaliana, the level of expression of a potent repressor of flowering known as FLOWERING LOCUS C (FLC) is a key factor in determining when flowering occurs. Our exploration of flowering-time control and the regulation of FLC expression have led us to study FLC chromatin. Below is a brief overview; a more detailed description is provided in some reviews listed below under Selected Publications (1-3).

Certain plant species do not flower unless they have experienced the prolonged cold of winter. This promotion of flowering by prolonged exposure to cold is known as vernalization (3). A vernalization requirement ensures that in temperate regions flowering does not occur in the fall season. In the fall, FLC is expressed to levels that prevent flowering. During winter, vernalization results in FLC repression which, in turn, permits vernalized plants to flower in the spring. The repression of FLC by vernalization is epigenetic in the sense that it is stable mitotically in the absence of the inducing signal, cold exposure. In the next generation, FLC is reset to the expressed state in which flowering is repressed. We have shown that the different epigenetic states of FLC expression are associated with a series of modifications to FLC chromatin, and we have characterized many of the components that are required for active FLC expression in the fall or for FLC repression in the spring (Selected Publications 4-14). For example, cold-mediated repression and all of the associated chromatin modifications require VERNALIZATION INSENSITIVE 3 (VIN3; ChromDB ID = VPGB1), which has the unique property of being expressed only after prolonged exposure to cold (9).

The vernalization-mediated repression of FLC is a useful model to understand some of the language of the plant histone code. The epigenetic repression of FLC can be induced by an environmental signal, exposure to cold, which is easy to administer in the lab. Thus we can assay FLC chromatin before, during and after vernalization, and address issues such as which modifications and components are required for stable epigenetic repression. One highlight of this approach is the finding that the plant equivalent of HETEROCHROMATIN PROTEIN 1 (HP1; ChromDB ID = CRD1) is required for maintenance of FLC repression after vernalization (6). A complex similar to Polycomb Repression Complex 2 (PRC2) of animals is involved in the initiation of FLC silencing. This is not surprising because PRC2 is involved in the initiation of gene silencing in animals. However, in animals, maintenance of PRC2-initiated repression requires Polycomb Repression Complex 1 (PRC1), and plant genomes do contain genes encoding PRC1 components. Apparently, HP1 can play a PRC1-like role in plants. Some of our recent work indicates that symmetrical dimethylation of arginine residues in histone H4 by At4g31120 (ChromDB ID=PRMT15, the putative homolog of human PRMT5) is also required for maintenance of FLC repression.



Selected Publications:
Reviews:

Schmitz RJ and Amasino RM. 2007 Vernalization: a model for investigating epigenetics and eukaryotic gene regulation in plants. Biochemica Biophysica Acta, in press.

Sung, S. and R. M. Amasino. 2006. Molecular genetic studies of the memory of winter. Journal of Experimental Botany 57(13):3369-77.

Amasino, R. M. 2004. Vernalization, competence, and the epigenetic memory of winter. Plant Cell 16: 2553-2559.

Research Papers:

Schmitz RJ, Hong L, Fitzpatrick KE, and Amasino RM. 2007. DICER-LIKE 1 and DICER-LIKE 3 Redundantly Act to Promote Flowering Via Repression of FLOWERING LOCUS C in Arabidopsis thaliana. Genetics 176, 1359-1362

Sung, S., Y., R. J. Schmitz and R. M. Amasino. 2006. A PHD finger protein involved in both the vernalization and photoperiod pathways in Arabidopsis. Genes and Development 20: 3244-3248.

Sung, S., Y. He, T. W. Eshoo, Y. Tamada, D. Shultis, L. Johnson., A. M. Lindroth, K. Nakahigashi, K. Goto, S. Khorasanizadeh, S. E. Jacobsen and R. M. Amasino. 2006. Epigenetic maintenance of the vernalized state in Arabidopsis requires like heterochromatin protein 1. Nature Genet. 38: 706-710.

Schmitz, R. J., L. Hong, S. Michaels, and R. M. Amasino. 2005. FRIGIDA-ESSENTIAL 1 interacts genetically with FRIGIDA and FRIGIDA-LIKE 1 to promote the winter-annual habit of Arabidopsis thaliana. Development 32: 5471-5478.

Kim, S. Y., Y. He, Y. Jacob, Y. S. Noh, S. Michaels and R. Amasino. 2005. Establishment of the vernalization-responsive, winter-annual habit in Arabidopsis requires a histone H3 methyl transferase. Plant Cell 17: 3301-3310.

Sung, S. and R. M. Amasino. 2004. Vernalization in Arabidopsis thaliana is mediated by the PHD finger protein VIN3. Nature 427: 159-164.

He, Y., M. R. Doyle and R. M. Amasino. 2004. PAF1 complex-mediated histone methylation of FLOWERING LOCUS C chromatin is required for the vernalization-responsive, winter-annual habit in Arabidopsis. Genes Dev. 18: 2774-2784.

Liu, J.,Y. He, R. M. Amasino and X. Chen. 2004. siRNAs targeting an intronic transposon in the regulation of natural flowering behavior in Arabidopsis. Genes Dev. 18: 2873-2878.

Michaels, S. D., I. C. Bezerra and R. M. Amasino. 2004. FRIGIDA-related genes are required for the winter-annual habit in Arabidopsis. Proc. Natl. Acad. Sci. USA 101: 3281–3285.

He, Y., S. D. Michaels and R. M. Amasino. 2003. Regulation of flowering time by histone acetylation in Arabidopsis. Science 302: 1751-1754.

Noh, Y. S. and R. M. Amasino. 2003. PIE1, an ISWI family gene, is required for FLC activation and floral repression in Arabidopsis. Plant Cell 15: 1671-1682.