Possible involvement of FLC in natural variation of activity to enhance the late flowering phenotype of the clock mutant lhy cca1 under continuous light

LHY and CCA1 play key roles in circadian clock functions and photoperiodic flowering in Arabidopsis. Double loss of function of LHY and CCA1 genes (lhy cca1) accelerated flowering under long days or short days, but the lhy cca1 delayed flowering time under constant-light (LL) conditions. FCA encodes an RNA binding protein that plays key roles in the autonomous pathway. Loss of function of FCA increases mRNA level of a major floral repressor gene, FLC. A mutation in FLC gene partially suppressed the late flowering phenotype of the lhy cca1 in LL. Based on this result, we have proposed that FLC may be involved in this process. Increased level of FLC mRNA in fca is responsible for the delay of flowering and the late flowering phenotype of the fca is suppressed by vernalization. In this paper, we isolated an enhancer of the late-flowering phenotype of the lhy cca1 in LL based on natural variation of two Arabidopsis accessions, Columbia and Landsberg erecata. The enhancer was named ELLCL and mapped near the FLC. This result suggested that the gene responsive to ELLCL might be FLC and was consistent with our previous results. The late-flowering phenotype of lhy cca1 was insensitive to vernalization. By contrast, flowering time of the fca was accelerated by vernalization as reported. These results suggested that posttranslational, but not the transcriptional, regulation of FLC might be involved in this process.