Vernalisation pathway
The vernalisation pathway (Figure 1.1) promotes flowering in plants that have been exposed to prolonged low temperatures. Winter annual accessions of Arabidopsis respond to vernalisation and contain the alleles of FLC and FRI, which play a central role in the vernalisation response (see also section 1.4.1; Lee et al., 1993; Clarke and Dean, 1994; Sheldon et al., 1999; Sheldon et al., 2000) . The correct function of these genes is normally lacking in early flowering accessions, many of which carry loss-of-function fri alleles; Ler also has a transposon inserted in the first intron of FLC (Gazzani et al., 2003) .
The FRI gene
FRI is an upstream positive regulator of FLC. FRI does not repress flowering in the absence of FLC activity (Johanson et al., 2000; Michaels and Amasino, 2001) . FRI encodes an unknown protein, which is predicted to contain coiled-coil domains in two positions (Johanson et al., 2000).
The repressor of flowering FLC Protein
The MADS box protein FLC is a repressor of flowering (Michaels and Amasino, 1999; Sheldon et al., 1999) . The expression of FLC is high in winter-annual accessions or in autonomous pathway mutants and is mainly expressed in the vegetative apex and roots (Michaels and Amasino, 2000) . The expression levels of FLC remain high throughout vegetative growth, but are low during reproductive growth, this suggests that developmental processes may override the repression of flowering caused by FLC expression (Michaels and Amasino, 1999; Sheldon et al., 1999) . FLC expression is progressively reduced during vernalisation treatment and reaches trough levels after approximately six weeks vernalisation. Repression of FLC expression is maintained when vernalised plants are returned to warmer growth conditions (Michaels and Amasino, 2001) , but is reset through meiosis so that the progeny of vernalised plants again show high FLC expression.
Although FLC plays a central role in the vernalisation process, flc null mutants still respond to vernalisation (Michaels and Amasino, 2001; Reeves and Coupland, 2001) . This suggests that vernalisation can also promote flowering in an FLC independent manner.
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