The autonomous pathway
Mutations that delay flowering under any photoperiod and confer a response to vernalisation were placed in the autonomous pathway.
Genes in the autonomous pathway include LD, FCA, FY, FPA, FVE, FLD and FLK. Mutations in each of these genes lead to an increase in the levels of FLC mRNA and FLC protein (Michaels and Amasino, 1999; Sheldon et al., 1999; Rouse et al., 2002) . Most of the genes in this group have been cloned and suggest that the autonomous pathway represents different biological processes. FCA contains an RNA binding motif and a WW domain, which is thought to be involved in protein-protein interactions (Bork et al., 1994; Macknight et al., 1997) . FCA is able to bind to RNA in vitro (Macknight et al., 1997; Macknight et al., 2002) . FCA is able to regulate its own expression by promoting cleavage and polyadenylation of its own third intron; this auto-regulation is under developmental control and requires the WW domain (Quesada et al., 2003) .
The FVE proteins represents a second biochemical function involved in FLC regulation. FVE encodes AtMSI4, a putative retinoblastoma-associated protein that participates in a protein complex that represses FLC transcription through a histone deacetylation mechanism (Ausin et al., 2004). Additionally, it has recently been shown to be a negative regulator of the CBF/DREB pathway involved in the cold acclimatisation (Ausin et al., 2004; Kim et al., 2004) .
Autonomous Pathway Genes
Double mutant analysis suggests that autonomous pathway genes do not act in a linear hierarchy. For example, the fy mutation does not enhance the flowering phenotype seen in fca plants, suggesting that they act in the same pathway. Similar logic suggests that FVE and FPA act in a linear pathway. The double mutant fpa fy is lethal, and the combination of fve with either fca or fy mutants leads to a later flowering time than is seen in the single mutants alone (Koornneef et al., 1998b) . FY binds to the WW domain of FCA, and is involved in the processing of the 3' end of transcripts (Simpson et al., 2003) . FLC seems to be particularly sensitive to the impairment of the function of this complex, causing an increase in FLC mRNA abundance. From work on perichimal chimaeras, in which flowering was not delayed when FCA was expressed in epidermal cell layers, it is thought that FCA promotes flowering in a cell non-autonomous manner (Furner et al., 1996) .
RNA recognition
Like FCA, FPA also contains a RNA recognition motif. Mutations in FPA result in extremely delayed flowering, whilst overexpression of FPA in Arabidopsis causes early flowering in noninductive short days. Like FCA, FPA is expressed most strongly in developing tissues (Schomburg et al., 2001) .
Forward to Autonomous pathway part 2