Phylogeographical studies of Glycine soja: implicating the refugium during the Quaternary glacial period and large-scale expansion after the Last Glacial Maximum

Wild soybean (Glycine soja Sieb. & Zucc.), the progenitor of cultivated soybean (Glycine max (L.) Merr.), is widely distributed in the Sino-Japanese Floristic Region (SJFR). Therefore, it is an excellent model organism to study the effect of Quaternary climatic changes on the distribution and migration of plant taxa in the SJFR. To investigate the phylogeography of G. soja, a total of 632 individuals representing 52 populations throughout the species distribution range were genotyped by using the sequencing data of a nuclear locus, AF105221, and a chloroplast locus, trnQ-rps16. We detected a total of 23 haplotypes from two loci, including five common and 18 rare haplotypes. Among them, 17 rare haplotypes were limited to Northeast Asia (Northeast China (NEC) and Korea) and the Yangzi River basin (middle and downstream of the Yangzi River (MDYR) and the eastern end of Southwest China (SWC)). Moreover, two common haplotypes were detected throughout the species distribution wide range. All the haplotypes from Japan and the Korean peninsula were also found in China. The haplotype distribution patterns of the two loci suggested that Northeast Asia (NEC and Korea) and the Yangzi River basin (MDYR and the eastern end of SWC) might have been the refugia for G. soja during the Quaternary glacial period, and G. soja expanded rapidly after the end of the Last Glacial Maximum. There was a land bridge between East China, the Korean peninsula, and Japan that permitted gene flow among populations of these regions in the ice age during the Quaternary.