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Integration of Flowering Signals in Winter-Annual Arabidopsis1

Summary: Integration of Flowering Signals in
Winter-Annual Arabidopsis1
Scott D. Michaels2
, Edward Himelblau2,3
, Sang Yeol Kim, Fritz M. Schomburg, and Richard M. Amasino*
Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706 (E.H., F.M.S., R.M.A.);
and Department of Biology, Indiana University, Bloomington, Indiana 47405 (S.D.M., S.Y.K.)
Photoperiod is the primary environmental factor affecting flowering time in rapid-cycling accessions of Arabidopsis
(Arabidopsis thaliana). Winter-annual Arabidopsis, in contrast, have both a photoperiod and a vernalization requirement for
rapid flowering. In winter annuals, high levels of the floral inhibitor FLC (FLOWERING LOCUS C) suppress flowering prior to
vernalization. FLC acts to delay flowering, in part, by suppressing expression of the floral promoter SOC1 (SUPPRESSOR OF
OVEREXPRESSION OF CONSTANS1). Vernalization leads to a permanent epigenetic suppression of FLC. To investigate how
winter-annual accessions integrate signals from the photoperiod and vernalization pathways, we have examined activation-
tagged alleles of FT and the FT homolog, TSF (TWIN SISTER OF FT), in a winter-annual background. Activation of FT or TSF
strongly suppresses the FLC-mediated late-flowering phenotype of winter annuals; however, FT and TSF overexpression does
not affect FLC mRNA levels. Rather, FT and TSF bypass the block to flowering created by FLC by activating SOC1 expression.
We have also found that FLC acts as a dosage-dependent inhibitor of FT expression. Thus, the integration of flowering signals
from the photoperiod and vernalization pathways occurs, at least in part, through the regulation of FT, TSF, and SOC1.
Flowering time in most plant species is regulated by
a combination of endogenous controls and environ-


Source: Amasino, Richard M. - Department of Biochemistry, University of Wisconsin at Madison


Collections: Biology and Medicine