Mapping genetic loci for flowering time,maturity, and photoperiod insensitivity in soybean

Time of flowering and maturity in soybean (Glycine max (L.) Merr) are important reproductive characters of agronomic interest. These traits are useful for developing soybean cultivars with a wider geographical adaptation. The objective of this research was to use molecular markers to identify chromosomal regions that control traits for flowering time, maturity and photoperiod insensitivity in soybean. Two single-cross populations, IX132 (PI 317.336 × `Corsoy') consisting of 101 progeny, and IX136 (PI 317.334B × `Corsoy') consisting of 100 progeny, were used. Days to R1 (the day when 50% of the plants in a plot have an open flower at one of the top nodes with a fully expanded leaf) was observed among F_6:7 RI lines in the field during 1991 and 1992 and in the growth chamber at 12 h and 20 h photoperiods using fluorescent and incandescent lamps. Days to R3 (the number of days after emergence when 50% of the plants in a plot had presented the first 5 mm pod at one of the top four nodes with a fully expanded leaf was observed in the field during 1991 and in the growth chamber with 12 h photoperiod. Days to R7 (the number of days after emergence when 50% of pods in a plot had mature pod color) was observed in the field in 1991. A total of 139 markers (88 RFLPs and 51 SSRs) in the IX132 population and 125 markers (73 RFLPs and 52 SSRs) in the IX136 population were used to map quantitative trait loci (QTL) affecting these traits. Results show that a large-effect QTL for days to R1, R3, and R7, and photoperiod insensitivity was found at the same location on linkage group (LG) C2 in both populations. This result suggests that photoperiod insensitivity, flowering time, and maturity may be controlled by the same gene(s) or by tightly clustered genes in the same chromosomal region. In addition to the large effect QTL, minor QTL were also detected controlling the four traits in both populations. Minor QTL account for as much as 17.8% and 12.1% of phenotypic variance in populations IX132 and IX136, respectively. Thus, time of flowering, maturity, and photoperiod insensitivity in these soybean populations are proposed to be controlled by a major QTL with a large effect and modified by several minor QTL.     

Molecular markers for the E2 and E3 genes controlling flowering and maturity in soybean

Natural variation in flowering time may play a role in the adaptation of plants to various environments, and understanding the genetic basis of flowering and maturity would facilitate the development of early maturing cultivars. Molecular markers for the E2 and E3 loci, which control the time of flowering and maturity in soybean (Glycine max), were developed in this study. Single nucleotide-amplified polymorphism (SNAP) markers were developed from the nonsense mutation in E2 (GmGIa), which is a circadian clock-controlled gene. The E2- and e2-specific SNAP markers were validated using six E2 isolines. The soybean E3 gene is a photoreceptor phytochrome A (GmPhyA3) gene, and a co-dominant marker was designed based on sequence deletions within the E3 allele. A multiplex PCR assay using three primers for the E3 gene allowed allelic discrimination based on the sizes of PCR products. Furthermore, this E3 marker successfully detected two alleles in a single reaction when two types of DNA were pooled. These markers determined the genotypes of our mapping population previously reported to detect flowering quantitative trait loci close to the E2 and E3 loci, confirming that the mutations are responsible for the early flowering phenotype. The use of SNAP markers for E2 and a co-dominant marker for E3 is a simple, fast, and reproducible method, requiring only PCR and agarose gel electrophoresis. The molecular resources developed in this study could accelerate marker-assisted selection and cultivar development for short-season areas in a soybean breeding program.     

Natural variation in GmGBP1 promoter affects photoperiod control of flowering time and maturity in soybean

The present study screened for polymorphisms in coding and non‐coding regions of the GmGBP1 gene in 278 soybean accessions with variable maturity and growth habit characteristics under natural field conditions in three different latitudes in China. The results showed that the promoter region was highly diversified compared with the coding sequence of GmGBP1. Five polymorphisms and four haplotypes were closely related to soybean flowering time and maturity through association and linkage disequilibrium analyses. Varieties with the polymorphisms SNP_‐796G, SNP_‐770G, SNP_‐307T, InDel_‐242normal, SNP_353A, or haplotypes Hap‐3 and Hap‐4 showed earlier flowering time and maturity in different environments. The shorter growth period might be largely due to higher GmGBP1 expression levels in soybean that were caused by the TCT‐motif with SNP_‐796G in the promoter. In contrast, the lower expression level of GmGBP1 in soybean caused by RNAi interference of GmGBP1 resulted in a longer growth period under different day lengths. Furthermore, the gene interference of GmGBP1 also caused a reduction in photoperiod response sensitivity (PRS) before flowering in soybean. RNA‐seq analysis on GmGBP1 underexpression in soybean showed that 94 and 30 predicted genes were significantly upregulated and downregulated, respectively. Of these, the diurnal photoperiod‐specific expression pattern of three significant flowering time genes GmFT2a, GmFT5a, and GmFULc also showed constantly lower mRNA levels in GmGBP1‐i soybean than in wild type, especially under short day conditions. Together, the results showed that GmGBP1 functioned as a positive regulator upstream of GmFT2a and GmFT5a to activate the expression of GmFULc to promote flowering on short days.     

水稻开花光周期调控相关基因研究进展

水稻开花调控是一个极其复杂的生命过程,由自身遗传因素和外界环境共同决定。光周期途径是调控水稻开花的关键途径,在这个途径中成花素基因Hd3a和RTF1处于核心地位,其上游调控途径主要包括Hd1依赖途径、Ehd1依赖途径及不依赖于Hd1和Ehd1的途径。这3条途径在汇集了光信号的各种信息后,将信号在Hd3a和RTF1处整合,并通过成花素形式将信息传递给下游开花基因,调控水稻开花。本文从成花素、光信号感受基因和昼夜节律基因、成花素上游调控基因、互作蛋白和下游调控基因等几方面阐述水稻开花光周期调控相关基因的研究现状,为水稻开花调控的深入研究提供参考。     

Flowering in time: genes controlling photoperiodic flowering in Arabidopsis.

Successful sexual reproduction in plants relies upon the strict coordination of flowering time with favourable seasons of the year. One of the most important seasonal cues for the model plant Arabidopsis thaliana (Arabidopsis) is day length. Genes influencing flowering time in Arabidopsis have been isolated, some of which are involved in the perception and signalling of day length. This review discusses recent progress that has been made in understanding how Arabidopsis integrates environmental and internal signals to ensure a sharp transition to flowering and new insights on the role of the circadian clock in controlling the expression of genes that promote flowering in response to day length.     

Divergence of flowering genes in soybean

Soybean genome sequences were blasted with Arabidopsis thaliana regulatory genes involved in photoperiod-dependent flowering. This approach enabled the identification of 118 genes involved in the flowering pathway. Two genome sequences of cultivated (Williams 82) and wild (IT182932) soybeans were employed to survey functional DNA variations in the flowering-related homologs. Forty genes exhibiting nonsynonymous substitutions between G. max and G. soja were catalogued. In addition, 22 genes were found to co-localize with QTLs for six traits including flowering time, first flower, pod maturity, beginning of pod, reproductive period, and seed filling period. Among the genes overlapping the QTL regions, two LHY/CCA1 genes, GI and SFR6 contained amino acid changes. The recently duplicated sequence regions of the soybean genome were used as additional criteria for the speculation of the putative function of the homologs. Two duplicated regions showed redundancy of both flowering-related genes and QTLs. ID 12398025, which contains the homeologous regions between chr 7 and chr 16, was redundant for the LHY/CCA1 and SPA1 homologs and the QTLs. Retaining of the CRY1 gene and the pod maturity QTLs were observed in the duplicated region of ID 23546507 on chr 4 and chr 6. Functional DNA variation of the LHY/CCA1 gene (Glyma07g05410) was present in a counterpart of the duplicated region on chr 7, while the gene (Glyma16g01980) present in the other portion of the duplicated region on chr 16 did not show a functional sequence change. The gene list catalogued in this study provides primary insight for understanding the regulation of flowering time and maturity in soybean.     

Association between genes controlling flowering time and shoot sodium accumulation in the Triticeae

Saline hydroponic studies of cytogenetic stocks of wheat have shown that near isogenic lines carrying contrasting alleles Vrn (vernalisation requirement) or Ppd (photoperiod requirement) genes accumulate less sodium when the dominant allele is present. These dominant alleles also confer early flowering. The genetic control of response to salt stress is discussed with respect to Vrn and Ppd genes. The data suggest that both these genes have pleiotropic effects on sodium accumulation. Salt treatment did not appear to switch on any genes which control sodium accumulation and it is concluded that the intrinsic genetic make-up of the plant determines fitness under salt stress conditions.     

显性E1基因背景下大豆开花和成熟期的全基因组关联分析

【目的】深入解析大豆开花期和成熟期的遗传基础,发掘控制性状的重要基因组区间,为分子标记辅助选择育种和新基因克隆提供依据。【方法】以224份携带显性E1基因的大豆种质为试验材料,在4个种植环境下调查表型数据,采用R-mrMLM软件包中的6种多位点关联分析模型对大豆开花和成熟期进行全基因组关联分析。【结果】共检测到91个开花期和83个成熟期QTNs（quantitative trait nucleotides）,其中6个开花期和10个成熟期QTNs能在多环境中检测到。这些环境稳定QTNs分布于15个区间大小在90~490 Kb的单倍型（基因组）内,并有6个基因组区间为本研究新检测到。【结论】研究表明显性E1基因背景下大豆开花和成熟期的QTN构成复杂,位于5号染色体39.52~40.01Mb等15个基因组区间是该群体中控制大豆开花期或成熟期的重要位点。     

Genome-wide identification of flowering time genes associated with vernalization and the regulatory flowering networks in Chinese cabbage

Flowering time (Ft) is the most important characteristic of Chinese cabbage with high leaf yields and late-flowering are favorable traits, while little knowledge on genes involved in Ft and the flowering mechanism in this crop. In this study, we conducted genome-wide RNA-seq analysis using an inbred Chinese cabbage ‘4004’ line in response to vernalization and compared the Ft gene expression with radish crop. A number of Ft genes which play roles in flowering pathways were performed quantitative RT-PCR analysis to verify the regulatory flowering gene network in Chinese cabbage. We found that a total of 223 Ft genes in Chinese cabbage, and 50 of these genes responded to vernalization. The majority of flowering enhancers were upregulated, whereas most flowering repressors were downregulated in response to vernalization as confirmed by RT-qPCR. Among the major Ft genes, the expression of BrCOL1-2, BrFT1/2, BrSOC1/2/3, BrFLC1/2/3/5, and BrMAF was strongly affected by vernalization. In reference to comparative RNA-seq profiling of Ft genes, Chinese cabbage and radish revealed substantially different vernalization response in particular GA flowering pathway. Thus, this study provides new insight into functional divergence in flowering pathways and the regulatory mechanisms in Brassicaceae crops. Further analysis of the major integrator genes between early and late-flowering inbred lines facilitates understanding flowering trait variation and molecular basis of flowering in Chinese cabbage.     

QTL identification of flowering time at three different latitudes reveals homeologous genomic regions that control flowering in soybean

Since the genetic control of flowering time is very important in photoperiod-sensitive soybean (Glycine max (L.) Merr.), genes affecting flowering under different environment conditions have been identified and described. The objectives were to identify quantitative trait loci (QTLs) for flowering time in different latitudinal and climatic regions, and to understand how chromosomal rearrangement and genome organization contribute to flowering time in soybean. Recombinant inbred lines from a cross between late-flowering ‘Jinpumkong 2’ and early-flowering ‘SS2-2’ were used to evaluate the phenotypic data for days to flowering (DF) collected from Kamphaeng Saen, Thailand (14°01′N), Suwon, Korea (37°15′N), and Longjing, China (42°46′N). A weakly positive phenotypic correlation (r = 0.36) was found between DF in Korea and Thailand; however, a strong correlation (r = 0.74) was shown between Korea and China. After 178 simple sequence repeat (SSR) markers were placed on a genetic map spanning 2,551.7 cM, four independent DF QTLs were identified on different chromosomes (Chrs). Among them, three QTLs on Chrs 9, 13 and 16 were either Thailand- or Korea-specific. The DF QTL on Chr 6 was identified in both Korea and China, suggesting it is less environment-sensitive. Comparative analysis of four DF QTL regions revealed a syntenic relationship between two QTLs on Chrs 6 and 13. All five duplicated gene pairs clustered in the homeologous genomic regions were found to be involved in the flowering. Identification and comparative analysis of multiple DF QTLs from different environments will facilitate the significant improvement in soybean breeding programs with respect to control of flowering time.     

Comparative mapping in Arabidopsis and Brassica, fine scale genome collinearity and congruence of genes controlling flowering time

The model dicotyledonous plant, Arabidopsis thaliana , is closely related to Brassica crop species. It is intended that information concerning the genetic control of basic biological processes in Arabidopsis will be transferable to other species. Genome collinearity and its potential to facilitate the identification of candidate genes in Arabidopsis homologous to genes controlling important agronomic traits in Brassica was investigated. Genetic mapping in B. nigra identified two loci influencing flowering time (FT), with loci on linkage groups 2 and 8 explaining 53% and 12% of the total variation in FT, respectively. The CO gene exerts an important control over FT in A. thaliana , and B. nigra homologues of CO probably also play an important role in regulating FT. B. nigra homologues of CO were identified on linkage groups 2 and 8, the homologue on group 2 was coincident with the major locus controlling FT while the homologue on group 8 was within the 90% confidence interval of the weaker FT gene. The CO homologue on group 2 exhibits abundant allelic variation suggesting that it naturally controls a wide range of flowering times. Fine-scale A. thaliana/B. nigra comparative mapping demonstrated short-range collinearity between the genomes of Arabidopsis and Brassica . Eleven DNA fragments spaced over a 1.5 Mb contig in A. thaliana were used as RFLP probes in B. nigra . Three collinear representations of the A. thaliana contig were identified in B. nigra , with one interrupted by a large chromosomal inversion. Collinearity over this range will allow the resources generated by the Arabidopsis genome project to facilitate map-based cloning in Brassica crops.     

Regulation of flowering time using temperature,photoperiod and spermidine treatments in Anoectochilus roxburghii

This study investigated the effects of different temperatures, photoperiods and spermidine concentrations on the flowering time regulation of Anoectochilus roxburghii by measuring changes in the soluble sugar, soluble protein, malondialdehyde and proline contents, and the peroxidase, superoxide dismutase and catalase activities in A. roxburghii flower buds. The flowering time could be advanced under 25/20 °C (day/night), 16/8-h (day/night) long day conditions or low spermidine concentrations. The plants grew more rapidly and flowering rates were greater. The flowering time could be delayed under a low temperature of 20/15 °C or 8/16-h short day conditions, resulting in a low flowering rate. Under a high temperature of 30/25 °C or high spermidine concentrations, the plants could not flower normally and even died. There were significant differences in the seven measured indices among the various treatments. Thus, different treatments had significant effects on the flowering time regulation and flowering quality of A. roxburghii, providing a reliable theoretical basis for further studies on the flowering-related regulatory mechanisms of A. roxburghii.     

Comparative genomic analysis of soybean flowering genes

Flowering is an important agronomic trait that determines crop yield. Soybean is a major oilseed legume crop used for human and animal feed. Legumes have unique vegetative and floral complexities. Our understanding of the molecular basis of flower initiation and development in legumes is limited. Here, we address this by using a computational approach to examine flowering regulatory genes in the soybean genome in comparison to the most studied model plant, Arabidopsis. For this comparison, a genome-wide analysis of orthologue groups was performed, followed by an in silico gene expression analysis of the identified soybean flowering genes. Phylogenetic analyses of the gene families highlighted the evolutionary relationships among these candidates. Our study identified key flowering genes in soybean and indicates that the vernalisation and the ambient-temperature pathways seem to be the most variant in soybean. A comparison of the orthologue groups containing flowering genes indicated that, on average, each Arabidopsis flowering gene has 2-3 orthologous copies in soybean. Our analysis highlighted that the CDF3, VRN1, SVP, AP3 and PIF3 genes are paralogue-rich genes in soybean. Furthermore, the genome mapping of the soybean flowering genes showed that these genes are scattered randomly across the genome. A paralogue comparison indicated that the soybean genes comprising the largest orthologue group are clustered in a 1.4 Mb region on chromosome 16 of soybean. Furthermore, a comparison with the undomesticated soybean (Glycine soja) revealed that there are hundreds of SNPs that are associated with putative soybean flowering genes and that there are structural variants that may affect the genes of the light-signalling and ambient-temperature pathways in soybean. Our study provides a framework for the soybean flowering pathway and insights into the relationship and evolution of flowering genes between a short-day soybean and the long-day plant, Arabidopsis.     

Genome-wide association study for flowering time,maturity dates and plant height in early maturing soybean (Glycine max) germplasm

Background

Soybean (Glycine max) is a photoperiod-sensitive and self-pollinated species. Days to flowering (DTF) and maturity (DTM), duration of flowering-to-maturity (DFTM) and plant height (PH) are crucial for soybean adaptability and yield. To dissect the genetic architecture of these agronomically important traits, a population consisting of 309 early maturity soybean germplasm accessions was genotyped with the Illumina Infinium SoySNP50K BeadChip and phenotyped in multiple environments. A genome-wide association study (GWAS) was conducted using a mixed linear model that involves both relative kinship and population structure.

Results

The linkage disequilibrium (LD) decayed slowly in soybean, and a substantial difference in LD pattern was observed between euchromatic and heterochromatic regions. A total of 27, 6, 18 and 27 loci for DTF, DTM, DFTM and PH were detected via GWAS, respectively. The Dt1 gene was identified in the locus strongly associated with both DTM and PH. Ten candidate genes homologous to Arabidopsis flowering genes were identified near the peak single nucleotide polymorphisms (SNPs) associated with DTF. Four of them encode MADS-domain containing proteins. Additionally, a pectin lyase-like gene was also identified in a major-effect locus for PH where LD decayed rapidly.

Conclusions

This study identified multiple new loci and refined chromosomal regions of known loci associated with DTF, DTM, DFTM and/or PH in soybean. It demonstrates that GWAS is powerful in dissecting complex traits and identifying candidate genes although LD decayed slowly in soybean. The loci and trait-associated SNPs identified in this study can be used for soybean genetic improvement, especially the major-effect loci associated with PH could be used to improve soybean yield potential. The candidate genes may serve as promising targets for studies of molecular mechanisms underlying the related traits in soybean.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1441-4) contains supplementary material, which is available to authorized users.     

Mapping loci controlling flowering time in Brassica oleracea

The timing of the transition from vegetative to reproductive phase is a major determinant of the morphology and value of Brassica oleracea crops. Quantitative trait loci (QTLs) controlling flowering time in B. oleracea were mapped using restriction fragment length polymorphism (RFLP) loci and flowering data of F₃ families derived from a cabbage by broccoli cross. Plants were grown in the field, and a total of 15 surveys were made throughout the experiment at 5–15 day intervals, in which plants were inspected for the presence of flower buds or open flowers. The flowering traits used for data analysis were the proportion of annual plants (PF) within each F₃ family at the end of the experiment, and a flowering-time index (FT) that combined both qualitative (annual/biennial) and quantitative (days to flowering) information. Two QTLs on different linkage groups were found associated with both PF and FT and one additional QTL was found associated only with FT. When combined in a multi-locus model, all three QTLs explained 54.1% of the phenotypic variation in FT. Epistasis was found between two genomic regions associated with FT. Comparisons of map positions of QTLs in B. oleracea with those in B. napus and B. rapa provided no evidence for conservation of genomic regions associated with flowering time between these species.