International Journal of Plant Science
Flowering time and FLOWERING LOCUS C (FLC) RNA levels were analyzed in different accessions of Arabidopsis thaliana and in mixed genetic backgrounds resulting from crosses between accessions. Dominant alleles of FRIGIDA (FRI) promote accumulation of FLC RNA, which in turn promotes late flowering. Although the coding regions of sequenced FLC alleles are identical, some accessions have genetically weak alleles that do not promote late flowering in the presence of FRI. In this study, a new weak allele of FLC with open reading frame identity to previously sequenced alleles was isolated from a Niederzenz (Nd) accession. The FLC‐Nd allele accumulated less RNA in the presence of FRI than did the strong Columbia (Col) allele. The weak FLC‐Nd allele was semidominant in the mixed Nd/Col genetic background containing FRI, and a linear correlation between the level of FLC RNA and lateness of flowering was observed. However, late‐flowering transgressions with elevated levels of FLC RNA in the absence of FRI were also obtained from crosses between early‐flowering accessions Col and Nd. Moreover, compared to Nd, the weak Landsberg erecta (Ler) allele of FLC was recessive and not semidominant in the mixed Ler/Col genetic background. However, very early‐flowering transgressions lacking detectable FLC RNA were also obtained from crosses between FRI containing Col and Ler. The results indicate that modifier genes other than FRI influence the level and genetic activity of FLC RNA in different genetic backgrounds resulting from crosses between naturally occurring accessions of A. thaliana.