As an important food crop and oil crop, soybean(Glycine max [L.] Merr.) is capable of nitrogen-fixing by root nodule. Previous studies showed that GmNMH7, a transcription factor of MADS-box family, is associated with nodule development, but its specific function remained unknown. In this study, we found that GmN MH7 was specifically expressed in root and nodule and the expression pattern of GmNMH7 was similar to several genes involved in early development of nodule(GmENOD40-1, GmENOD40-2, GmNFR1 a, GmNFR5 a, and GmNIN) after rhizobia inoculation. The earlier expression peak of GmNMH7 compared to the other genes(GmENOD40-1, GmENOD40-2, GmNFR1 a, GmNFR5 a, and GmNIN) indicated that the gene is related to the nod factor(NF) signaling pathway and functions at the early development of nodule. Over-expression of GmNMH7 in hairy roots significantly reduced the nodule number and the root length. In the transgenic hairy roots, overexpression of GmN MH7 significantly down-regulated the expression levels of GmE NOD40-1, GmE NOD40-2, and GmN FR5α. Moreover, the expression of GmNMH7 could respond to abscisic acid(ABA) and gibberellin(GA_3) treatment in the root of Zigongdongdou seedlings. Over-expressing GmNMH7 gene reduced the content of ABA, and increased the content of GA_3 in the positive transgenic hairy roots. Therefore, we concluded that GmNMH7 might participate in the NF signaling pathway and negatively regulate nodulation probably through regulating the content of GA_3.
MA Wen-yaLIU WeiHOU Wen-shengSUN ShiJIANG Bing-junHAN Tian-fuFENG Yong-junWU Cun-xiang
Soybean(Glycine max[L.]Merr.)is a food and oil crop whose growth and yield are influenced by root and nodule development.In the present study,Gm NMHC5 was found to promote the formation of nodules in overexpressing mutants.In contrast,the number of nodules in Gmnmhc5 edited with CRISPR/Cas9 decreased sharply.In 35 S:Gm NMHC5 mutants,expression levels of genes involved in nodulation were significantly up-regulated.Both in vitro and in vivo biochemical analyses showed that Gm NMHC5 directly interacted with Gm GAI(a DELLA protein),and the content of gibberellin 3(GA_(3))in overexpressing mutants was lower than that in the wild type.These results revealed that Gm NMHC5 participates in the classical GA signaling pathway,and may regulate the content of GA_3 to match the optimal concentration required for nodule formation,thereby promoting nodulation by directly interacting with Gm GAI.A model illustrating the mechanism by which Gm NMHC5 promotes soybean nodulation is presented.
