GmFULa, a FRUITFULL homolog, functions in the flowering and maturation of soybean.

KEY MESSAGE: A FRUITFULL homolog GmFULa was cloned and found to play roles in the flowering and maturation of soybean. Soybean varieties exhibit great diversity in terms of flowering and maturation due to differences in their photoperiodic responses. The underlying mechanism remains unclear despite the fact that some upstream flowering genes have been studied. FRUITFULL (FUL) genes are one group of downstream flowering genes known to have major roles in reproductive transition, floral meristem identity, and floral organ identity. However, FUL homologs and their functions are poorly understood in soybean. Here, a soybean FUL homolog was cloned from the late-maturing photoperiod-sensitive soybean variety Zigongdongdou (ZGDD) and designated GmFULa. In ZGDD, GmFULa exhibited a terminal-preferential expression pattern, with higher expression in the root and shoot apices than in the middle parts. Diurnal rhythm analysis revealed that photoperiod regulates the GmFULa expression level but does not alter its diurnal rhythm. ZGDD was maintained under different photoperiod conditions (long day, LD; short day, SD; LD after 13 short days, SD13-LD) to assess GmFULa expression in newly expanded leaves and in the shoot apex. From this analysis, GmFULa expression was detected in the floral meristem, floral organs and their primordia; trifoliate leaves; and the inflorescence meristem, with the expression levels induced by SD and inhibited by LD. GmFULa expression was also associated with maturity in seven soybean varieties with different photoperiod sensitivities. Therefore, photoperiod conditions affect the expression level of GmFULa but not its diurnal rhythm. The gene plays pleiotropic roles in reproductive transition, flowering, and leaf development and is associated with maturity in soybean.

GmFT2a, a soybean homolog of FLOWERING LOCUS T, is involved in flowering transition and maintenance.

BACKGROUND: Flowering reversion can be induced in soybean (Glycine max L. Merr.), a typical short-day (SD) dicot, by switching from SD to long-day (LD) photoperiods. This process may involve florigen, putatively encoded by FLOWERING LOCUS T (FT) in Arabidopsis thaliana. However, little is known about the potential function of soybean FT homologs in flowering reversion. METHODS: A photoperiod-responsive FT homologue GmFT (renamed as GmFT2a hereafter) was cloned from the photoperiod-sensitive cultivar Zigongdongdou. GmFT2a gene expression under different photoperiods was analyzed by real-time quantitative PCR. In situ hybridization showed direct evidence for its expression during flowering-related processes. GmFT2a was shown to promote flowering using transgenic studies in Arabidopsis and soybean. The effects of photoperiod and temperature on GmFT2a expression were also analyzed in two cultivars with different photoperiod-sensitivities. RESULTS: GmFT2a expression is regulated by photoperiod. Analyses of GmFT2a transcripts revealed a strong correlation between GmFT2a expression and flowering maintenance. GmFT2a transcripts were observed continuously within the vascular tissue up to the shoot apex during flowering. By contrast, transcripts decreased to undetectable levels during flowering reversion. In grafting experiments, the early-flowering, photoperiod-insensitive stock Heihe27 promotes the appearance of GmFT2a transcripts in the shoot apex of scion Zigongdongdou under noninductive LD conditions. The photothermal effects of GmFT2a expression diversity in cultivars with different photoperiod-sensitivities and a hypothesis is proposed. CONCLUSION: GmFT2a expression is associated with flowering induction and maintenance. Therefore, GmFT2a is a potential target gene for soybean breeding, with the aim of increasing geographic adaptation of this crop.