Functional analysis of type II chalcone isomerase (<i>CHI</i>) genes in regulating soybean (<i>Glycine max L</i>.) nodule formation

Biological nitrogen fixation (BNF) is the most cost-effective and environmentally benign method for nitrogen fertilization. Isoflavones are important signaling factors for BNF in leguminous plants. Whether chalcone isomerase (<i>CHI</i>), the key enzyme gene in the flavonoid synthesis pathway, contributes to soybean (<i>Glycine max</i>) nodulation has not yet been fully clarified. In the present study, we identified the functions of three types of <i>GmCHI</i> for BNF using a hairy root system. The results showed that <i>GmCHI1A</i> and <i>GmCHI1B1</i> positively increased nodulation while <i>GmCHI1B2</i> did not, with the <i>GmCHI1A</i> gene having a greater effect than <i>GmCHI1B1</i>. Meanwhile, the daidzein and genistein contents were significantly increased in composite plants overexpressing <i>GmCHI1A</i> and reduced in composite plants, thus interfering with <i>GmCHI1A</i>. However, overexpression of <i>GmCHI1B1</i> significantly increased the content of glycitein but not daidzein, genistein content implied that homologous genes exhibit functional differentiation. These results provide a reference for subsequent studies on improving nitrogen fixation in soybeans and providing functional genes for the improvement of new varieties.