Assistant Professor
Director, IU Yeast-Two-Hybrid Facility

Ph.D. University of Wisconsin-Madison, 1999
Postdoctoral Fellow, University of Wisconsin-Madison, 1999-2003

Program Affiliation: Molecular Biology & Genetics | Plant Biology

Research Groups Affiliation: Biochemistry | Development | Evo-Devo | Genetics | Plant Biology

Phone: 812/856-0302
Fax: 812/855-6082
Email Scott

Michaels Lab Website

Introduction to flowering

The transition from vegetative growth to flowering marks a major transition in the life cycle of plants; meristems that had been producing leaves and stems switch to producing the reproductive structures (i.e. flowers). The proper timing of this transition is critical for the reproductive success and is highly regulated by both the developmental state of the plant and environmental signals, such as daylength and temperature. Of particular interest to our lab, is the promotion of flowering by prolonged exposure to cold (i.e. winter), known as vernalization. Biennial plants, for example, have an obligate requirement for vernalization before flowering can occur. This cold requirement prevents flowering from occurring prior to winter and promotes rapid flowering in the favorable conditions of spring (Fig 1). Vernalization has a number of interesting characteristics. For example, vernalization requires an extended period of cold treatment, typically 1-3 months at 0-4°C for maximal response and, once established, the vernalized state is stable throughout subsequent mitotic divisions, but is reset following meiosis. Thus vernalized plants have a permanent “memory” of cold exposure.

Current research interests

In our lab, we utilize Arabidopsis as a model system to study the regulation of flowering time. In addition to the general advantages (small sized, rapid generation time, sequenced genome, and a large collection of gene knock-out lines), flowering in Arabidopsis is regulated by both photoperiod (flowering is accelerated by long days) and vernalization. Early-flowering lab strains of Arabidopsis do not have a vernalization requirement for early flowering, however, there are two genetic situations where Arabidopsis is late flowering and vernalization responsive.
The first occurs naturally. In contrast to most early flowering (summer-annual) lab strains of Arabidopsis, many naturally occurring accessions of Arabidopsis are relatively late flowering unless exposed to cold (vernalization). This winter-annual habit is due to the synergistic interaction of two genes: FLOWERING LOCUS C ( FLC) and FRIGIDA (FRI). FLC encodes a MADS domain-containing transcription factor that acts to inhibit flowering and FRI is required for high levels of expression (Fig 2, 3).

Figure 2. A local model for the regulation of flowering by FLC.

The second is a group of late-flowering vernalization-responsive mutants known as the autonomous-pathway mutants. Loss-of-function mutations in any of these six genes (LUMINIDEPENDENS, FCA, FLOWERING LOCUS D, FPA, FY, and FVE) results in an upregulation of FLC, and a late-flowering phenotype. Thus the wild-type function of the autonomous pathway genes is to promote flowering by repressing FLCexpression (Fig 2). In both cases, vernalization results in an epigenetic shut off of FLC expression (i.e. even after the cold treatment has ended, FLC levels remain suppressed for the remainder of the plant's life, Fig 1-3). Thus the epigenetic suppression of FLC may be part of the plant’s memory of vernalization.

FLC is a key regulator of flowering time, integrating signals from at least three flowering pathways. Our current research is based on the further elucidation of the role that FLC plays in the regulation of flowering time, both in Arabidopsis and other species. Using forward and reverse genetics and microarray analysis, we are working to identify the upstream regulators and downstream targets of FLC. We are also working to take what has been learned about the regulation of flowering in our model system (Arabidopsis) and applying it to other species.

Kim, S.Y., Yu, X., and Michaels, S.D. 2008. Regulation of flowering time in response to changing light quality. Plant Physiology, in press.

Veley, K.M. and Michaels, S.D. 2008. Functional redundancy and new roles for genes of the autonomous floral-promotion pathway. Plant Physiology, 147: 682-695.

Jacob, Y. and Michaels, S.D. 2008. Peering through the pore; the role of AtTPR in nuclear transport and development. Plant Signaling and Behavior, 3 (1) p. 62-64.

Michaels, S.D. 2008. Integration of photoperiodic timing and vernalization. In: Photoperiodism: Seasonal Time Measurement. Edited by R. J. Nelson, D. Denlinger and D. Somers. Oxford University Press.

Jacob, Y., Mongkolsiriwatana, C., Veley, K., Kim, S.Y., and Michaels, S.D. 2007. The nuclear pore protein AtTPR is required for RNA homeostasis, flowering time, and auxin signaling. Plant Physiology, 144(3): p.1383-90.

Kim, S.Y. and S.D. Michaels, 2006. SUPPRESSOR OF FRI 4 encodes a nuclear-localized protein that is required for delayed flowering in winter-annual Arabidopsis. Development, 133(23): p. 4699-707.

Kim, S.Y., He, Y., Jacob, Y., Noh, Y.S., Michaels, S.D., and Amasino, R.M. 2005. Establishment of the vernalization-responsive, winter-annual habit in Arabidopsis requires a putative histone H3 methyl transferase. Plant Cell, 17:3301-10.

Michaels, S.D., Himelblau, E., Kim, S.Y., Schomburg, F.M., and Amasino, R.M. 2005. Integration of flowering signals in winter-annual Arabidopsis. Plant Physiology, 137: 149-156.

Michaels, S.D., Bezzerra, I.C., and Amasino, R.M. 2004. FRIGIDA-related genes are required for the winter-annual habit in Arabidopsis., PNAS,101: 3281-5.

Michaels, S.D., He, Y., Scortecci, K.C., and Amasino, R.M. 2003. Attenuation of FLOWERING LOCUS C activity as a mechanism for the evolution of summer-annual flowering behavior in Arabidopsis., PNAS, 100(17): 10102-7.