Cloning And Functional Analysis Of Tof5,A Locus Of Soybean Adaptated To High Latitude

Soybean（Glycine max（L.）Merr.）is a typical short-day（SD）plant and is highly sensitive to photoperiod.Photoperiod sensitivity determines the adaptation of soybean to different latitudes.Cultivated soybean was domesticated from its wild progenitor（Glycine soja Sieb.&Zucc.）.Photoperiod responsiveness is a key factor limiting the geographic distribution of cultivated soybean and its wild ancestor.At present,the genetic basis of soybean adaptation to high latitudes has been well understood but not completely clarified.The genetic basis of the adaptation in wild soybean remains poorly understood.Therefore,it is of great significance to identify genes related to latitude adaptation of wild and cultivated soybean,and elucidate the evolutionary and molecular mechanism underlying the latitude adaptation of them.In this study,genome-wide association studies（GWAS）was used to detect a novel locus Time of Flowering 5（Tof5）,which controls flowering time and yield under long day（LD）conditions.We demonstrated the molecular mechanism of Tof5 regulating soybean of flowering,revealed as well as the genetic basis of wild and cultivated soybean adaptation to high latitudes.The major results are as following:1.GWAS analysis were performed with whole-genome resequencing data of a panel of 372soybean accessions from high latitudes and two-year flowering phenotype data collected in Harbin,China.A significant association locus for flowering time on chromosomes 5 was identified,named Time of flowering 5（Tof5）.2.Linkage disequilibrium block analysis was used to determine that region contains a homolog of Arabidopsis thaliana FRUITFULL（FUL）may be the candidate gene of Tof5.By population genetics,chromosomal segment substitution line,sequencing,CRISPR/Cas9 and overexpression technology we further showed that Tof5 locus was encoded by FUL2a gene.3.Under LD conditions,the legume-specific flowering repressor E1 directly bind to the promoter of Tof5 gene to suppress its transcription.Tof5 protein in turn physically associate with the promoters of two important FLOWERING LOCUS T（FT）genes,FT2a and FT5a,to upregulate their expression,thus promoting flowering.4.The analysis of evolutionary and population genetics showed that two distinct alleles of Tof5 have undergone parallel selection in cultivated and wild soybean.The Tof5^H1 allele was strongly selected via artificial selection after the early domestication of cultivated soybean,while the Tof5^H2 allele was selected via natural selection in wild soybean,and in each case promoting the adaptation to high latitudes.In conclusion,a key locus Tof5,which underlys flowering time control in soybean under LD conditions was detected by GWAS,and proved that Tof5 is encoded by FUL2a.In this study,we showed that E1 protein represses the transcription of Tof5 and that Tof5 protein directly bind to the promoters of FT2a and FT5a to activate their expression,ultimately resulting in promoting flowering and maturity and reducing grain yield.In addition,Tof5 is a significant gene involved in high-latitude adaptation in both wild and cultivated soybean.Our study provides the first evidence that the adaptation of wild soybean in high latitudes.This research not only further improves the molecular regulatory network of soybean photoperiodic flowering under LD conditions,but also provides the important theoretical and practical basis for high-latitude adaptation and yield molecular breeding of soybean.