Functional analysis of type II chalcone isomerase (CHI) genes in regulating soybean (Glycine max L.) 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 (CHI), the key enzyme gene in the flavonoid synthesis pathway, contributes to soybean (Glycine max) nodulation has not yet been fully clarified. In the present study, we identified the functions of three types of GmCHI for BNF using a hairy root system. The results showed that GmCHI1A and GmCHI1B1 positively increased nodulation while GmCHI1B2 did not, with the GmCHI1A gene having a greater effect than GmCHI1B1. Meanwhile, the daidzein and genistein contents were significantly increased in composite plants overexpressing GmCHI1A and reduced in composite plants, thus interfering with GmCHI1A. However, overexpression of GmCHI1B1 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.