Summary: The Plant Cell, Vol. 13, 935­941, April 2001, www.plantcell.org © 2001 American Society of Plant Physiologists
Loss of FLOWERING LOCUS C Activity Eliminates the
Late-Flowering Phenotype of FRIGIDA and Autonomous
Pathway Mutations but Not Responsiveness to Vernalization
Scott D. Michaels and Richard M. Amasino1
Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison, Wisconsin 53706-1544
The MADS domain­containing transcription factor FLOWERING LOCUS C (FLC) acts as an inhibitor of flowering and is
a convergence point for several pathways that regulate flowering time in Arabidopsis. In naturally occurring late-flow-
ering ecotypes, the FRIGIDA (FRI) gene acts to increase FLC levels, whereas the autonomous floral promotion pathway
and vernalization act to reduce FLC expression. Previous work has shown that the Landsberg erecta allele of FLC,
which is not a null allele, is able to partially suppress the late-flowering phenotype of FRIGIDA and mutations in the au-
tonomous pathway. In this study, using a null allele of FLC, we show that the late-flowering phenotype of FRIGIDA and
autonomous pathway mutants are eliminated in the absence of FLC activity. In addition, we have found that the down-
regulation of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 by FRI and autonomous pathway mutants also is
mediated by FLC. Complete loss of FLC function, however, does not eliminate the effect of vernalization. Thus, FRI and
the autonomous pathway may act solely to regulate FLC expression, whereas vernalization is able to promote flower-
ing via FLC-dependent and FLC-independent mechanisms.
INTRODUCTION
The promotion of flowering in response to prolonged expo-
sure to cold temperatures is an adaptation to prevent plants

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

Collections: Biology and Medicine