Delayed flowering time in Arabidopsis and Brassica rapa by the overexpression of FLOWERING LOCUS C (FLC) homologs isolated from Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Chinese cabbage plants remain in the vegetative growth phase until they have experienced prolonged exposure to cold temperature, known as vernalization. This inhibition of flowering is caused by the high levels of FLOWERING LOCUS C (FLC) expression. To increase the product value of Chinese cabbage by inhibiting the floral transition, three genes (BrFLC1, BrFLC2, and BrFLC3) homologous to the AtFLC gene, which encodes a floral repressor, were isolated from the Chinese cabbage 'Chiifu'. These genes showed high similarity to AtFLC, although the putative BrFLC1 protein contained ten more residues than AtFLC. The BrFLC genes were expressed ubiquitously, except that BrFLC3 was not expressed in roots. BrFLC1 and BrFLC2 showed stronger expression than BrFLC3 in unvernalized and vernalized Chinese cabbage. The expression levels of the three BrFLC genes were lower in an early-flowering Chinese cabbage, suggesting that the BrFLC transcript level was associated with flowering time. Constitutive expression of the BrFLC genes in Arabidopsis significantly delayed flowering, which was also observed in transgenic Chinese cabbage overexpressing BrFLC3. These results suggest that the BrFLC genes act similarly to AtFLC. Our results provide a technique for controlling flowering time in Chinese cabbage and other crops to produce high yields of vegetative tissues.