Cloning and characterization of a homologue of the FLORICAULA/LEAFY gene in Ficus carica L., FcLFY, and its role in flower bud differentiation

Fig (Ficus carica L.) is high in fruit yield and nutritious, and easy to form flower buds. Fig tree, differing from many other fruit trees, has unique flower bud differentiation and fruit-bearing characteristics. Its flower bud (inflorescence) differentiation takes place throughout the shoot elongation period, and it occurs with fruits simultaneously. The entire process of flower bud differentiation to fruit ripening can be completed in one growing season. Studying the unique flowering characteristics of fig provides an important theoretical basis for its cultivation, flowering regulation, fruit production, and molecular breeding. However, the molecular mechanism of flower bud differentiation in fig has not been elucidated, so identifying the relevant genes is essential for understanding the characteristics of fig flower bud differentiation. Here, we isolated a FLORICAULA/LEAFY homologue gene from fig, FcLFY, and identified its function and expression patterns. FCLFY contains a 1377 bp open reading frame and encodes 458 amino acids. The amino acid sequence has a typical LFY/FLO family domain, containing a unique glycine rich region. Moreover, FcLFY expressed the highest in apical bud meristem of fig. In addition, Arabidopsis transgenic lines L23 and L28, which overexpressed FcLFY, bolted 8-9 days and flowered 6 days earlier than WT, while the line C7, which rescued the abnormal flower phenotype of lfy-15 mutant, flowered 8 days earlier than the mutant. Analysis with qRT-PCR further showed that the expressions of flowering promoting genes, including AP1, LFY, CAL and SEP3 were up-regulated while the flowering inhibitory genes FLC and TFL1 were down-regulated in the FcLFY transgenic Arabidopsis. Taken together, FcLFY over-expression shortened the period of vegetative growth, promoted early flowering, partially complemented the phenotypic defects of ify15 mutant and increased the expression of floral meristem and flower organ genes in Arabidopsis, indicating that FcLFY is involved in the flower bud differentiation and plays an important role in apical meristem formation of fig. This study provides useful information for us to better understand the characterization and function of FeLFY in regulating flower initiation, and is helpful for establishing molecular breeding systems in fig.