Diversifying Selection on Flavanone 3-Hydroxylase and Isoflavone Synthase Genes in Cultivated Soybean and Its Wild Progenitors

Soybean isoflavone synthase (IFS) and flavanone 3-hydroxylase (F3H) are two key enzymes catalyzing the biosynthesis of isoflavonoids and flavonoids, both of which play diverse roles in stress responses. However, little is known about the evolutionary pattern of these genes in cultivated soybean and its wild progenitors. Herein, we investigated the nucleotide polymorphisms in Isoflavone synthase (IFS1, IFS2) and Flavanone 3-hydroxylase (F3H2) genes from 33 soybean accessions, including 17 cultivars (Glycine max) and 16 their wild progenitors (Glycine soja). Our data showed that the target genes shared the levels of nucleotide polymorphism with three reference genes involved in plant-microbe interactions, but possessed a much higher nucleotide polymorphism than other reference genes. Moreover, no significant genetic differentiation was found between cultivated soybean and its wild relatives in three target genes, despite of considering bottleneck and founder effect during domestication. These results indicate that IFS and F3H genes could have experienced gene introgressions or diversifying selection events during domestication process. Especially, F3H2 gene appears to evolve under positive selection and enjoy a faster evolutionary rate than IFS1 and IFS2 genes.