Using landscape genomics to infer genomic regions involved in environmental adaptation of soybean genebank accessions

Understanding how crops adapt to specific environmental conditions is becoming increasingly important in the face of accelerating climate change, but the genetics of local adaptation remain little understood for many crops. Landscape genomics can reveal patterns of genetic variation that indicate adaptive diversification during crop evolution and dispersal. Here, we examine genetic differentiation and association signatures with environmental gradients in soybean (Glycine max) germplasm groups from China that were inferred from the USDA Soybean Germplasm Collection (N = 17,019 accessions) based on population structure and passport information. We recover genes previously known to be involved in soybean environmental adaptation and report numerous new candidate genes in selection signatures implicated by genomic resources such as the genome annotation and gene expression datasets to function in flowering regulation, photoperiodism and stress reaction cascades. Linkage disequilibrium network analysis suggested functional relationships between genomic regions with selection signatures, consistent with the polygenic nature of environmental adaptation. We tested whether haplotypes associated with environmental adaptation in China were present in 843 North American and 160 European soybean cultivars and found that haplotypes in major genes for early maturity have been selected during breeding, but also that a large number of haplotypes exhibiting putative adaptive variation for cold regions at high latitudes are underrepresented in modern cultivars. Our results demonstrate the value of landscape genomics analysis in genebank germplasm as a starting point for the study of crop environmental adaptation and have the potential to inform future research efforts focused on improved soybean adaptation. Functional validation of candidate genes will support understanding of their adaptive roles and likely enable the transfer of beneficial adaptive variation into modern breeding germplasm.