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.

Assessing the numbers of SNPs needed to establish molecular IDs and characterize the genetic diversityof soybean cultivars derived from Tokachi nagaha

The development of a core set of SNP molecular markers that could be widely used in soybean genetic research would greatly facilitate research into the genetic diversity of soybean.We conducted an analysis of Tokachi nagaha and 137 of its descendant soybean cultivars using 4044 SNP markers with the goal of determining the appropriate number of single-nucleotide polymorphisms(SNPs)needed to construct unambiguous molecular IDs and characterize genetic diversity based on a genetic distance matrix correlation method.When the number of SNPs was held constant,the number of accession pairs that could be distinguished increased as the polymorphism informative content(PIC)value of the SNPs increased.A core panel of 20 selected SNPs from 11 linkage groups with a mean PIC value of 0.3703 and a range of 0.3640–0.3749 was able to identify almost all of the accession pairs in our study[9445 pairs(99.92%)].The eight accession pairs that could not be identified with this core SNP set all originated from the same province and some of them had the same parental cultivars.The molecular IDs of the 138 accessions were constructed using the core 20 SNPs.It is known that both the number of SNPs and PIC values should be considered when SNPs are selected for use in the analysis of genetic diversity.In this study,when the PIC value was 0.3460,the correlation coefficient between the genetic distance matrices associated with a panel of 200 SNPs and the total population was>0.800,indicating satisfactory correlation.Our high-accuracy,high-resolution core SNP panel for germplasm fingerprinting and our findings about assessing genetic diversity will likely markedly improve the management and utilization efficiency of soybean germplasm resources.

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.

Zinc-finger protein GmZF351 improves both salt and drought stress tolerance in soybean

Abiotic stress is one of the most important factors reducing soybean yield. It is essential to identify regulatory factors contributing to stress responses.A previous study found that the tandem CCCH zincfinger protein Gm ZF351 is an oil level regulator. In this study, we discovered that the Gm ZF351 gene is induced by stress and that the overexpression of Gm ZF351 confers stress tolerance to transgenic soybean. Gm ZF351 directly regulates the expression of Gm CIPK9 and Gm SnRK, leading to stomata closing, by binding to their promoter regions, which carry two CT(G/C)(T/A)AA elements.Stress induction of Gm ZF351 is mediated through reduction in the H3K27me3 level at the Gm ZF351locus.TwoJMJ30-demethylase-likegenes,Gm JMJ30-1 and Gm JMJ30-2, are involved in this demethylationprocess.Overexpressionof Gm JMJ30-1/2 in transgenic hairy roots enhances Gm ZF351 expression mediated by histone demethylation and confers stress tolerance to soybean.Yield-related agronomic traits were evaluated in stable Gm ZF351-transgenic plants under mild drought stress conditions. Our study reveals a new mode of Gm JMJ30-Gm ZF351 action in stress tolerance, in addition to that of Gm ZF351 in oil accumulation. Manipulation of the components in this pathway is expected to improve soybean traits and adaptation under unfavorable environments.

A PP2C-1 Allele Underlying a Quantitative Trait Locus Enhances Soybean l O0-Seed Weight

Cultivated soybeans may lose some useful genetic loci during domestication. Introgression of genes from wild soybeans could broaden the genetic background and improve soybean agronomic traits. In this study, through whole-genome sequencing of a recombinant inbred line population derived from a cross between a wild soybean ZYD7 and a cultivated soybean HN44, and mapping of quantitative trait loci for seed weight, we discovered that a phosphatase 2C-1 （PP2C-1） allele from wild soybean ZYD7 contributes to the increase in seed weight/size. PP2C-1 may achieve this function by enhancing cell size of integument and activating a subset of seed trait-related genes. We found that PP2C-1 is associ- ated with GmBZR1, a soybean ortholog of Arabidopsis BZR1, one of key transcription factors in brassi- nosteroid （BR） signaling, and facilitate accumulation of dephosphorylated GmBZR1. In contrast, the PP2C-2 allele with variations of a few amino acids at the N-terminus did not exhibit this function. More- over, we showed that GmBZR1 could promote seed weight/size in transgenic plants. Through analysis of cultivated soybean accessions, we found that 40% of the examined accessions do not have the PP2C-1 allele, suggesting that these accessions can be improved by introduction of this allele. Taken together, our study identifies an elite allele PP2C-1, which can enhance seed weight and/or size in soybean, and pinpoints that manipulation of this allele by molecular-assisted breeding may increase production in soybean and other legumes/crops.