Variation at two flowering time genes within and among populations of Arabidopsis thaliana:: comparison with markers and traits

Flowering Locus C (FLC) and Frigida are two interacting genes controlling flowering time variation in Arabidopsis thaliana. Variation at these genes was surveyed in 12 A. thaliana populations sampled in France. These populations were also screened for variation at molecular markers [ 12 microsatellites and 19 cleaved amplified polymorphic sequence ( CAPS) markers] and at seven quantitative traits measured with and without vernalization. Seven populations were highly polymorphic at markers (H-S = 0.57 at microsatellites, 0.24 at CAPS) and showed heritable variation for bolting time and some other traits. Five populations were genetically fixed or nearly fixed. Q(ST) for bolting time without vernalization was significantly higher than F-ST, suggesting local divergent selection. One of the two haplotype groups at FLC (FLCA) was very predominant ( frequency of 99%). The first exon of Frigida showed elevated nonsynonymous variation, and nine loss-of-function mutations were found throughout the gene. The association between loss-of-function and earlier bolting was confirmed. Overall, 18 Frigida haplotypes were detected. The pattern of variation at Frigida was largely similar to that found at markers and traits, with the same populations being fixed or highly diverse. Metapopulation dynamics is thus probably the main factor shaping genetic variation in A. thaliana. However, F-ST for functional (FRI) vs. nonfunctional ( FRI.) haplotypes was significantly higher than F-ST at markers. This suggested that loss-of-function at Frigida is under local selection for flowering time.