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要旨

The switch from vegetative to reproductive phase, culminating in flowering
has been defined as a critical event in the life cycle of Arabidopsis, given the
fact that it is an out-come of closely interacting multiple pathways responding
to both internal and external cues. The current model on flowering, framed
in four major pathways, identifies the floral repressor FLC, which encodes a
MADS domain protein, as a key determinant of the vernalization pathway. Natural
accessions of Arabidopsis vary greatly in their levels of FLC expression,
which is reflected in widely varying flowering times.
The Arabidopsis Genome Initiative has identified at least five MADS box
paralogues of FLC, amongst which MAF2 (AT5G65050) has been characterized
as a moderate repressor of flowering, with a specific role of preventing
premature vernalization response (Ratcliffe et al. 2002). Coupled to this is the
observation that each of these paralogues expresses several splice variants,
the roles of which remain undefined. Since several alleles with major indels
in FLC have been described, we surveyed a set of 45 natural accessions
for major indels in FLC paralogues. We found that such instances are rare
and restricted to non-coding sequences. In addition, RT-PCR revealed little
variation with respect to expression of transcripts corresponding to these
paralogues in about 100 accessions. Currently, we are further dissecting
MAF2 function by comparing the phenotypes derived from over-expressing
three reported and a novel iso-form from Columbia vis-à-vis full-length
genomic region in different genetic backgrounds. In a related effort, we shall
be carrying out a global-expression profiling of MAF2 T-DNA insertion mutant
in response to inductive day length.