| Soybean(Glycine max(L.)Merr.)is a typical short-day(SD)plant,and it is sensitive to the photoperiod.For a late-maturing variety(Zigongdongdou,ZGDD),it undergoes reproductive growth only when the day length becomes shorter than a critical length.Continuous SD treatment significantly accelerates the flowering and maturation of ZGDD.However,the effect of SD can be relieved when ZGDD transferred from SD to long-day(LD)conditions: the vegetative growth is promoted but the reproductive growth is inhibited,the apical meristem differentiates into vegetative organ from reproductive organ.The phenomenon of flowering reversion in soybean suggesting the presence of a ?floral-inhibitor? under LD.Flowering Locus T(FT)is an integrator that converges the signals from several flowering pathways.In soybean,at least 10 FT homologs have been identified.GmFT2 a and GmFT5 a were induced under SD condition,and promote flowering in soybean.GmFT4 has been noted to be strongly induced by LD conditions,and function in delaying flowering when ectopically expressed in Arabidopsis,suggesting that the soybean FT-like genes might have undergone functional divergence.However,it remains unclear whether other flowering-inhibiting FT homologs are existed in soybean.In this study,we performed a qRT-PCR analysis on the expression of FT family genes in ZGDD plants during flowering reversion and found 3 LD-specific genes(GmFT1a,GmFT1 b and Gm FT4).We cloned GmFT1 a from ZGDD and performed a systematic study.GmFT1 a was highly expressed in leaves under LD condition,the GUS marker gene driven by the promoter of GmFT1 a was highly expressed in the vascular tissue,and GmFT1a-GFP fusion protein was also located in the nucleus and in the cytoplasm.By analysing the expression of GmFT1 a in different varieties,we found that the expression of GmFT1 a were lower in early-maturing varieties,but were relative higher in the late-maturing varieties.Furthermore,GmFT1 a had a relative higher expression under LD than SD in almost all of these varieties,which was opposite to the flowering promoters Gm FT2 a and GmFT5 a.To determine whether E1 affects GmFT1 a expression,we examined GmFT1 a expression in the maturity gene(E)near-isogenic lines(NILs)and the E1 overexpressed transgenic soybean lines.The results showed that a majority of the NILs with the dominate genotype(E1)had relative higher GmFT1 a expression than NILs with the recessive genotype(e1);Moreover,in the E1 overexpressed transgenic soybean lines,the GmFT1 a expression pattern was elevated compared with that in wild-type.By using a Dual-Luciferase assay,we found that presence of the E1 protein significantly increased the levels of LUC activity under the control of GmFT1 a promoter.To investigate the function of Gm FT1 a,a construct containing the GmFT1 a CDS driven by the CaMV35 S promoter,was transformed into the mid-maturing soybean variety Jack,in which variety the expression of GmFT1 a was very low.The overexpression of GmFT1 a can significantly delay soybean flowering and maturation.Furthermore,compared to wild type plants,the expression of the flowering-promoting gene GmFT2 a was significantly lower in the leaves of the GmFT1 a overexpression plants.By analyzing the transcriptome of the GmFT1 a transgenic plants,we identified several flowering-related genes that respond to the overexpression of GmFT1 a in soybean.Based on the results of the present study and previous reports,we proposed a ?teeter-board‘ model: The FT homologs have functionally diverged in soybean.The balance between flowering-inhibiting(GmFT1a/GmFT4)and flowering-promoting(GmFT2a/GmFT5a)FT homologs may specify vegetative vs.reproductive development.Taken together,this finding provides a clear evidence that the GmFTs have functionally diverged in soybean.The balance between flowering-inhibiting(GmFT1a/GmFT4)and flowering-promoting(GmFT2a/GmFT5a)FT homologs may determine the development of soybean.GmFT1 a might provide a new molecular tool for the growth period regulation of soybean. |
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