Map-based Cloning And Functional Analysis Of Tof16,a Key Locus Of Soybean Adaptation To Low Latitude

Soybean is an important economic crop,which provides more than a quarter of the world's food protein and animal feed.More than half of the soybeans are produced in the tropics.Soybean is very sensitive to changes in photoperiod as a typical shortday plant,which hinders the yields of soybean growing in tropics.Up to now,the genetic basis of soybean adaptation to the tropic regions has yet to be fleshed out.In this study,Genome-Wide Association Studies(GWAS)and map-based cloning of parental population were used to detect a new locus called Tof16 that regulates soybean flowering and yield in low latitudes.We also elucidated the molecular mechanism of Tof16 regulating soybean of flowering.This research further revealed the genetic basis of soybean adaptation to tropical regions.The main results are as follows:1.A total of 329 soybean varieties planted in low latitude areas were collected and re-sequenced.Through GWAS analysis,a significant correlation locus on chromosome 16 with flowering time of soybean was detected,and this locus was named Time of Flowering 16(Tof16).2.The parental population was used for fine mapping of Tof16 and Tof16 was located in the 120 kb region of chromosome 16.And we further proved that Tof16 locus was encoded by LHY1 a gene by sequencing and CRISPR/cas9 technology.3.Under short-day conditons,Tof16 directly binds the promoter of E1,thereby inhibiting the transcription of E1,releasing the transcription of FT2 a and FT5 a which inhibited by E1,and promotes flowering of soybean.4.Tof16 and J independently but additively regulate flowering time,maturity and grain yield in soybean,and double homozygous recessive tof16 and j could significantly prolong soybean flowering period and improve soybean yield.5.During soybean adaptation from temperate origin into tropics,the weaky mutational alleles in both tof16 and j were firstly selected,and more null alleles were occurred subsequently on top of those weak alleles and further selected suggesting stepwise selection of natural mutations of both Tof16 and J.In conclusion,the key locus Tof16 was detected by GWAS and biparental population map-based cloning,and proved that Tof16 is encoded by LHY1 a.Tof16promoted soybean flowering by directly binding to E1 promoter under short-day conditons.In addition,Tof16 and J independently but additively regulate flowering time and grain yield in soybean.Furthermore,we revealed the genetic genomic basis of soybean adaptation to low latitude.Introducing the allelic variation loci detected in this study into the main soybean varieties may reduce the limitations of soybean planting areas in China,and increase the yield of soybean in China.