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Soybean (Glycine max) is a typical short‐day plant, but has been widely cultivated in high‐latitude long‐day (LD) regions because of the development of early‐maturing genotypes which are photoperiod‐insensitive. However, some early‐maturing varieties exhibit significant responses to maturity under different daylengths but not for flowering, depicting an evident photoperiodic after‐effect, a poorly understood mechanism. In this study, we investigated the postflowering responses of 11 early‐maturing soybean varieties to various preflowering photoperiodic treatments. We confirmed that preflowering SD conditions greatly promoted maturity and other postflowering developmental stages. Soybean homologs of FLOWERING LOCUS T (FT), including GmFT2a, GmFT3a, GmFT3b and GmFT5a, were highly accumulated in leaves under preflowering SD treatment. More importantly, they maintained a high expression level after flowering even under LD conditions. E1 RNAi and GmFT2a overexpression lines showed extremely early maturity regardless of preflowering SD and LD treatments due to constitutively high levels of floral‐promoting GmFT homolog expression throughout their life cycle. Collectively, our data indicate that high and stable expression of floral‐promoting GmFT homologs play key roles in the maintenance of photoperiodic induction to promote postflowering reproductive development, which confers early‐maturing varieties with appropriate vegetative growth and shortened reproductive growth periods for adaptation to high latitudes. Summary statement: The photoperiodic after‐effect of early‐maturing soybean varieties is caused by the maintenance of high‐level expression of floral‐promoting GmFTs. This phenomenon indicates that maturity exhibits a stronger photoperiod sensitivity than flowering time, which ensures an appropriate vegetative growth and shortened reproductive growth of early‐maturing soybean varieties to adapt to high latitudes with significant changes in photoperiods from long day to short day in the growing season. [ABSTRACT FROM AUTHOR]

CONSTANS (CO) plays a critical role in the photoperiodic flowering pathway. However, the function of soybean CO orthologs and the molecular mechanisms in regulating flowering remain largely unknown. This study characterized the natural variations in CO family genes and their association with flowering time and maturity in soybeans. A total of 21 soybean CO family genes (GmCOL s) were cloned and sequenced in 128 varieties covering 14 known maturity groups (MG 0000-MG X from earliest to latest maturity). Regarding the whole genomic region involving these genes, GmCOL1 , GmCOL3 , GmCOL8 , GmCOL9 , GmCOL10 , and GmCOL13 were conserved, and the remaining 15 genes showed genetic variation that was brought about by mutation, namely, all single-nucleotide polymorphisms (SNPs) and insertions-deletions (InDels). In addition, a few genes showed some strong linkage disequilibrium. Point mutations were found in 15 GmCOL genes, which can lead to changes in the potential protein structure. Early flowering and maturation were related to eight genes (GmCOL1 / 3 / 4 / 8 / 13 / 15 / 16 / 19). For flowering and maturation, 11 genes (GmCOL2 / 5 / 6 / 14 / 20 / 22 / 23 / 24 / 25 / 26 / 28) expressed divergent physiognomy. Haplotype analysis indicated that the haplotypes of GmCOL5-Hap2 , GmCOL13-Hap2/3 , and GmCOL28-Hap2 were associated with flowering dates and soybean maturity. This study helps address the role of GmCOL family genes in adapting to diverse environments, particularly when it is necessary to regulate soybean flowering dates and maturity. [ABSTRACT FROM AUTHOR]

Appropriate flowering and maturity time are important for soybean production. Four maturity genes E1, E2, E3 and E4 have been molecularly identified and found to play major roles in the control of flowering and maturity of soybean. Here, to further investigate the effect of different allele combinations of E1-E4, we performed Kompetitive Allele Specific PCR (KASP) assays based on single nucleotide polymorphisms (SNPs) at these four E loci, and genotyped E1-E4 genes across 308 Chinese cultivars with a wide range of maturity groups. In total, twenty-one allele combinations for E1-E4 genes were identified across these Chinese cultivars. Various combinations of mutations at four E loci gave rise to the diversity of flowering and maturity time, which were associated with the adaptation of soybean cultivars to diverse geographic regions and farming systems. In particular, the cultivars with mutations at all four E loci reached flowering and maturity very early, and adapted to high-latitude cold regions. The allele combinations e1-as/e2-ns/e3-tr/E4, E1/e2-ns/E3/E4 and E1/E2/E3/E4 played important roles in the Northeast China, Huang-Huai-Hai (HHH) Rivers Valley and South China regions, respectively. Notably, E1 and E2, especially E2, affected flowering and maturity time of soybean significantly. Our study will be beneficial for germplasm evaluation, cultivar improvement and regionalization of cultivation in soybean production. [ABSTRACT FROM AUTHOR]

Soybean [Glycine max (L.) Merr.] is a photoperiod‐sensitive crop, and the photoperiod response determines the ecological adaptability of soybean genotypes. Critical photoperiod is the dividing daylength between photoperiod sensitivity and photoperiod insensitivity phases and is one of the most important indicators of photoperiod sensitivity. However, the appropriate experimental treatment and calculation method for quantifying the critical photoperiod are poorly documented. To characterize the photoperiod response of genotypes, 72 soybean genotypes belonging to 14 different maturity groups (MG 0000–MG X) were included, and five photoperiod treatments of 12‐, 14‐, 16‐, 18‐, and 20‐h daylength were conducted in the consecutive 3 yr from 2015 to 2017. The piecewise linear regression model based on the median function was used to determine the critical photoperiod. The results showed that the photoperiodic responses of soybean genotypes were significantly different among various MGs. The critical photoperiod of MG 0000 was 16.4 h d−1, whereas those of MG 000 to MG I, MG II to MG III, MG IV, MG V to MG VIII, and MG IX to MG X were 15.7 to 15.8, 15.3, 14.7, 13.4 to 13.7, and ≤12 h d−1, respectively. A significant negative linear relationship between the critical photoperiod and relative maturity group (RMG) was found. It is of particular importance for the quantification of soybean photoperiod response and precise prediction of the developmental process. More importantly, the critical photoperiod obtained in this study will help breeders to synchronize the flowering time of parents from distant geographic origins and break the reproductive isolation among different ecotype cultivars. [ABSTRACT FROM AUTHOR]

Soybean is planted in a wide span of the world, and flowering and maturity time is an important trait determining soybean yield formation and adaptation. Maturity loci E1, E2, E3 and E4 were frequently reported as the most influential genetic loci for soybean flowering and maturity. To understand the allelic variation and assess the phenological traits of cultivars with different E allelic combinations in natural environments, 251 cultivars of maturity group (MG) I–V were field tested in 42 locations across four sub-regions in the Huang-Huai-Hai and Northwest region of China and genotyped with KASP markers for E1–E4 loci. The results indicated that mutant alleles were only found in the E1 and E2 locus, all of the cultivars carried functional alleles in the E3 and E4 loci in this area, with the frequency of mutant allele to be higher in early maturity groups (MGs) than late MGs. Among nine E allelic combinations in this area, one photoperiodic insensitive mutation in E2 loci (E1/e2-ns/E3-Ha/E4 and E1/e2-ns/E3-Mi/E4) made up the largest proportion (25.10 and 18.33%), while two photoperiodic insensitive mutations in both E1 and E2 loci (e1-as/e2-ns/E3-Ha/E4) (1.20%) occupied the lowest proportion in this panel. The major combinations of E locus for MGI, MGII and MG III in this area were E1/E2-dl/E3-Mi/E4, E1/e2-ns/E3-Mi/E4 and E1/e2-ns/E3-Ha/E4, respectively. Cultivars carrying e1-as/e2-ns/E3-Ha/E4 genotype flowered earliest (34 days) on average, 7.6 days earlier than the latest-flowering E haplotype (E1/e2-ns/E3-Ha/E4). This study provided an opportunity to detect the E allelic combinations in the Huang-Huai-Hai River Valley and the Northwest China, which would facilitate the improvement of soybean adaptation in the future. [ABSTRACT FROM AUTHOR]