Maturity time is an essential phenotypic measure of ecological adaptability of soybean and an important trait related to its yield formation. The study of promoters and expression patterns of major maturity genes E1 and E2 would provide basis for the study of gene function and molecular regulatory network of maturity time and lay foundation for adaptability improvement and yield increase in soybean.

The promoter sequences of major maturity genes E1 and E2 were analyzed through the promoter cis-element analysis website PlantCARE, and the important regulatory elements were detected. The promoters of E1 and E2 were cloned, the GUS vectors were constructed, and transformation of Arabidopsis was performed to detect GUS activity in different tissues and organs of transgenic plants. Under low light and strong light conditions, the expression levels of E1 and E2 were compared between long day and short day conditions. The expression levels of E1 and E2 were detected in soybean varieties of different maturity groups, which is for the analysis of correlation between expression levels and maturity time of soybean varieties.

Both E1 and E2 promoters contained multiple photoresponsive elements such as AE-box, Box4 and G-box, E1 promoter also contained auxin-response, abolic acid-response elements, and E2 promoter also contained low temperature-response, drought-response elements and meristem expression elements. In GUS activity detection of transgenic Arabidopsis, E1 promoter had strong transcriptional activity in all organs of the plant, and transcriptional activity of E2 promoter in fibrovascular tissues of seedling hypocotyl, leaf and root was relatively strong. Under both low light and strong light conditions, the expression level of E1 was significantly higher in long day than in short day. Under low light conditions, the expression level of E2 was higher in short day than in long day. Under strong light conditions, the expression level of E2 was higher in long day than in short day. With the increase of maturity time of different soybean varieties, expression level of E1 increased gradually, while E2 expression level did not change regularly.

The promoter of E1 gene was a widely expressed promoter, and its expression level was significantly regulated by photoperiod and significantly correlated with the maturity time of soybean varieties. The promoter of E2 was strongly expressed in vascular tissues of various organs, the photoperiodic regulation mode of this gene was different under strong light and low light conditions, and there was no significant correlation between expression level of E2 and maturity time.

Soybean is a short day crop that is sensitive to photoperiod, and it maybe lead to premature or late flowering when it is planted in different ecological areas. Therefore, in the application of ms1 (male sterility 1) basic population for recurrent selection in different ecological regions, there are problems such as the flowering time unsynchronization between local donor parents and acceptor sterile plants and low introduction rate. The purpose of this study is to construct ms1 basic recurrent population adapted to three ecological regions for improving the probability of flowering time synchronization between donor parents and acceptor sterile plants and reveal the changes of maturity genes E1 and E2 genotypes and phenotype of each population after two rounds of cross-fertilize for providing evidence for improvement of the flowering and maturity time of soybeans.

We used 528 donor parents from different ecological regions and the ms1 basic population as materials. The donor parents were genotyping with the KASP markers of maturity genes E1 and E2 reported by previous research. The donor parents were classified according to E1 and E2 genotypes and mixed with seeds of ms1 basic population respectively, and these populations were planted in different ecological areas according to the suitable genotypes of each region for two rounds of cross-fertilize in two years. Northeast ecological region population was planted in Hulunbuir, Inner Mongolia and Chengde, Hebei, respectively. Huang-Huai-Hai ecological region population was planted in Shijiazhuang, Hebei and Xuchang, Henan. South ecological region population was planted in Guangzhou, Guangdong. Seeds harvested from different ms1 populations were planted in Sanya, Hainan every winter. The flowering and maturity time of donor parents and ms1 basic population were investigated, and the proportions of E1 and E2 genotypes in populations of different region were calculated.

According to genotypes of maturity genes E1 and E2, the donor parents were divided into four groups E1E1/E2E2, E1E1/e2e2, e1e1/E2E2 and e1e1/e2e2 with ratios of 12.1%, 65.0%, 19.3%, and 3.6%, respectively. In the ms1 basic population, the late flowering genotype E1E1/E2E2 had the highest proportion (48.6%), and the flowering time of the population was late, mainly concentrated in 45-51 days. After two rounds of import by cross-fertilize, the percentage of target genotype e1e1/e2e2 increased from 33.0% to 51.6% in Hulunbuir of Northeast China, and the percentage of the e1e1/e2e2 genotype increased from 1.6% to 8% in Chengde. The percentage of target genotype e1e1/E2E2 increased from 18% to 23.1% in Shijiazhuang of Huang-Huai-Hai ecological area, and the percentage of E1E1/e2e2 increased from 12.5% to 30% in Xuchang, respectively. The percentage of E1E1/E2E2 remains above 80% in Guangzhou of South ecological region. The proportion of heterozygous genotypes of target imported genotypes was also increasing in the population. After two rounds of cross-fertilize, there were significant differences in flowering time among ms1 populations of different ecological regions, indicating that phenotypes of different populations also changed with the change of genotype of flowering genes.

Importing genotype of donor parents into the ms1 population based on their genotypes of flowering genes can increase the frequency of suitable genotypes in each ecological region, construct ms1 basic recurrent populations adapted to different ecological regions, increase the probability of flower time synchronization of local donor parents and acceptor ms1 sterile plants, achieve open pollination, gene aggregation and accumulation in soybean, and enrich the genetic diversity of the population, further improve breeding efficiency.