Cloning and characterization of the LFY homologue from Chinese cabbage (Brassica rapa subsp. pekinensis)

Flowering is critical to the growth and development of plants, and LFY gene homologues play a major role in flowering initiation. To understand the genetic and molecular mechanisms underlying floral initiation and development in Brassica rapa subsp. pekinensis, BrpLFY, a homologue of LFY, was cloned using RT-PCR. Sequence analysis showed that the cDNA sequence of BrpLFY is 1,341 bp in length, with an ORF of 1,245 bp encoding a predicted protein of 415 amino acids. The predicted protein showed a high degree of identity with LFY homologues from other angiosperm species. Real-time PCR analysis showed that BrpLFY mRNA was detected in all tissues during plant development from the vegetative state to fully differentiated flowers, and its expression was highest in the cotyledon and lowest in the root. BrpLFY expression in the shoot apex increased gradually during vegetative growth and increased dramatically at stage 1 of flower bud differentiation. The relative expression peaked at stage 5 and then decreased in later stages. Moreover, the trend in BrpLFY expression level change in the shoot apex was similar regardless of variety or vernalization method. The relative expression of BrpLFY in leaves gradually decreased with leaf development. We overexpressed the gene in Arabidopsis thaliana using the floral dip method, and examined flowering time in wild-type and transgenic plants. Overexpression of BrpLFY specifically caused early flowering; the transgenic plants flowered 10-14 d earlier than did wild-type plants, and leaf number decreased by 0.5-1 when the plants bolted. Real-time PCR analysis showed that the expression of BrpLFY in transgenic Arabidopsis was higher than in wild-type plants. These results indicate that BrpLFY plays a role in promoting flowering in Chinese cabbage.