Regulation of soybean stem growth habit:A ten-year progress report

Stem growth habit dictates plant architecture and influences flowering and podding(seed setting),making it an essential morphological and breeding agronomic trait of soybean(Glycine max).Stem growth habit in soybean is affected by photoperiod and environment and is determined by genetic variation at major genes.Classical genetic analysis identified two critical loci,designated Determinacy 1(Dt1)and Determinacy 2(Dt2).Dt1 is an ortholog of Arabidopsis thaliana TERMINAL FLOWER1(TFL1)and specifies an indeterminate stem growth habit,whereas Dt2 specifies a semi-determinate growth habit.MADS-box proteins,including Dt2,SUPPRESSOR OF OVEREXPRESSION OF CO1(GmSOC1)and MADS-box genes downregulated by E1(GmMDE),repress Dt1 expression.Photoreceptors encoded by the E3 and E4 loci regulate the expression of soybean FLOWERING LOCUS T(GmFT)orthologs via circadian clock genes and E1,and GmFTs compete with Dt1 to regulate stem growth habit.Study of the molecular mechanism underlying the regulation of stem growth habit in soybean has focused on the repression of Dt1 expression.Here we provide an overview of progress made in elucidating the genetic and molecular bases of stem growth habit in soybean,with emphasis on the molecular components responsible for integrating photoperiodic flowering and stem growth habit.

The MADS-box transcription factor GmFULc promotes GmZTL4 gene transcription to modulate maturity in soybean

Flowering time and maturity are crucial agronomic traits that affect the regional adaptability of soybean plants.The development of soybean cultivars with early maturity adapted to longer days and colder climates of high latitudes is very important for ensuring normal ripening before frost begins.FUL belongs to the MADS-box transcription factor family and has several duplicated members in soybeans.In this study,we observed that overexpression of GmFULc in the Dongnong 50 cultivar promoted soybean maturity,while GmFULc knockout mutants exhibited late maturity.Chromatin immunoprecipitation sequencing(ChIP-seq)and RNA sequencing(RNA-seq)revealed that GmFULc could bind to the CArG,bHLH and homeobox motifs.Further investigation revealed that GmFULc could directly bind to the CArG motif in the promoters of the GmZTL3 and GmZTL4 genes.Overexpression of GmZTL4 promoted soybean maturity,whereas the ztl4 mutants exhibited delayed maturity.Moreover,we found that the cis element box 4 motif of the GmZTL4 promoter,a motif of light response elements,played an important role in controlling the growth period.Deletion of this motif shortened the growth period by increasing the expression levels of GmZTL4.Functional investigations revealed that short-day treatment promoted the binding of GmFULc to the promoter of GmZTL4 and inhibited the expression of E1 and E1Lb,ultimately resulting in the promotion of flowering and early maturation.Taken together,these findings suggest a novel photoperiod regulatory pathway in which GmFULc directly activates GmZTL4 to promote earlier maturity in soybean.