Geographic distribution of the E1 family of genes and their effects on reproductive timing in soybean

Authors: DIETZ, NICHOLAS - University Of Missouri; COMBS-GIROIR, RACHEL - University Of Missouri; COOPER, GRACE - University Of Missouri; STACEY, MINVILUZ - University Of Missouri; MIRANDA, CARRIE - North Dakota State University; Bilyeu, Kristin

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2021
Publication Date: 9/29/2021
Citation: Dietz, N., Combs-Giroir, R., Cooper, G., Stacey, M., Miranda, C., Bilyeu, K.D. 2021. Geographic distribution of the E1 family of genes and their effects on reproductive timing in soybean. Biomed Central (BMC) Plant Biology. 21. Article 441. https://doi.org/10.1186/s12870-021-03197-x.
DOI: https://doi.org/10.1186/s12870-021-03197-x

Interpretive Summary: Soybean as a crop is made available as seed classified into different maturity groups that are optimized for different geographic locations. The maturity group system optimizes the soybean genetic responses to photoperiod in different latitudes. The major gene E1 has been shown to have the most effect on soybean photoperiod response, and recently two additional versions of the E1 gene were discovered in the soybean genome. This research describes the identification, breeding, and characterization of natural and induced mutations in the two new E1-Like genes in response to natural photoperiod field conditions. The mutant genes promoted earlier flowering and maturity, although they have not been used extensively in US breeding programs. The impact of these results is new soybean germplasm, molecular markers, and field validation of the genes' effects to fine tune photoperiod response for optimizing yield in different maturity group environments.

Technical Abstract: Background Soybean is an economically important crop which flowers predominantly in response to photoperiod. Several major loci controlling the quantitative trait for reproductive timing have been identified, of which allelic combinations at three of these loci, E1, E2, and E3, are the dominant factors driving time to flower and reproductive period. However, functional genomics studies have identified additional loci which affect reproductive timing, many of which are less understood. A better characterization of these genes will enable fine-tuning of adaptation to various production environments. Two such genes, E1La and E1Lb, have been implicated in flowering by previous studies, but their effects have yet to be assessed under natural photoperiod regimes. Results Natural and induced variants of E1La and E1Lb were identified and introgressed into lines harboring either E1 or its early flowering variant, e1-as. Lines were evaluated for days to flower and maturity in a Maturity Group (MG) III production environment. These results revealed that variation in E1La and E1Lb promoted earlier flowering and maturity, with stronger effects in e1-as background than in an E1 background. The geographic distribution of E1La alleles among wild and cultivated soybean revealed that natural variation in E1La likely contributed to northern expansion of wild soybean, while breeding programs in North America exploited e1-as to develop cultivars adapted to northern latitudes. Conclusion This research identified novel alleles of the E1 paralogues, E1La and E1Lb, which promote flowering and maturity under natural photoperiods. These loci represent sources of genetic variation which have been under-utilized in North American breeding programs to control reproductive timing, and which can be valuable additions to a breeder’s molecular toolbox.