Functional Analysis Of Soybean SOC1a And SOC1b In The Control Of Flowering Time

Soybean [Glycine max(L.)Merrill] is an important economic crop that provides protein and edible oil.Breeding soybean with high yield and quality has always been an important goal which pursued by breeders.Flowering time and maturity are key agronomic traits directly affecting regional adaptability and yield of soybean.SUPPRESSOR OF OVEREXPRESSION OF CO 1(SOC1)has been proved to be an essential flowering regulator,but its role in controlling flowering and yield in soybean is still under veil.There were four SOC1 homologous genes in soybean by alignment of At SOC1 sequence,and they are designated as SOC1a(Glyma.18G224500),SOC1b(Glyma.09G266200),SOC1c(Glyma.07G080900)and SOC1d(Glyma.03G019300)respectively.And the molecular mechanism of SOC1 s gene regulating soybean flowering was analyzed through Arabidopsis complementary assay,Clustered Regularly Interspaced Short Palindromic Repeats/Associated 9(CRISPR/Cas9),genetic transformation,RNA-seq,q RT-PCR,yeast two-hybrid system,chromatin immunoprecipitation(Ch IP),and Arabidopsis protoplast transient transformation.1.By complementation with Arabidopsis soc1 mutants,it was found that soybean SOC1 a and SOC1 b genes inhibited the late flowering phenotype of Arabidopsis soc1 mutants,resulting in the same flowering time as the wild type.The results showed that SOC1 a and SOC1 b had identical ability to induce flowering.And these suggested that SOC1 a and SOC1 b had conserved function in promoting flowering in Arabidopsis thaliana.2.Williams 82 was used as transgenic material.And the double homozygous mutants were obtained using the CRISPR/Cas9 system.Double homozygous soc1a1 b mutants delayed flowering and maturity under long day(LD)and short day(SD)conditions.And grain weight per plant of soc1a1 b mutants increased by 66% and76% under SD conditions in 2019 and 2020,respectively,which proved that SOC1 a and SOC1 b were promoting factors of soybean flowering and had the potential to increase grain weight per plant.3.RNA-seq and q RT-PCR indicated that SOC1 a and SOC1 b can regulate multiple flowering-related genes in leaves and stem apical meristem(SAM).The transcription levels of FT5 a and FT2 a in leaves and AP1 and LFY in SAM were significantly reduced,while SOC1 c,SOC1d and Dt1 in SAM were significantly increased than those of Williams 82 under LD and SD conditions.The results showed that SOC1 a and SOC1 b may promote flowering by activating the transcription of FT5 a and FT2 a in leaves and AP1 and LFY in SAM,respectively.4.In Arabidopsis protoplast transient transformation,SOC1 a and SOC1 b proteins enhanced FT5 a and FT2 a promoter activities,respectively.Chromatin immunoprecipitation(Ch IP-PCR)demonstrated that SOC1 a and SOC1 b could directly bind to the CAr G-motif of FT5 a promoter and FT2 a intron to promote their transcription expression,thereby promoting soybean flowering in soybean.It was demonstrated that SOC1 a and SOC1 b proteins induced flowering in soybean by directly binding to the two FT genes to activate their transcription.5.The yeast two-hybrid experiment verified that SOC1 a and SOC1 b interact to form homodimer and heterodimer possibly regulating the target genes.This study preliminarily elucidated the molecular mechanism of accelerated flowering of SOC1 a and SOC1 b under LD and SD conditions and further the molecular regulation network of photoperiodic flowering in soybean.Therefore,it provided provided the theoretical basis and genetic resources for soybean molecular design breeding.