Study On The Function And Mechanism Of GmBEHL1 In Soybean Nodulation

Symbiotic nitrogen fixation(SNF)between legumes and rhizobia is an important component of the nitrogen cycle of ecosystem.In the past,many studies have been conducted to investigate the relationship between roots and nodules in legumes with the focus on hormonal regulation.However,majority of them are still at the level of phenomenological observation,and little is known about the molecular mechanisms behind them.Previously,we identified NNC1(Nodule Number Control 1)as a key negative regulator of soybean nodulation.In a genetic screen to search for the interacting proteins of NNC1,we found a BES1/BZR1 family protein as a NNC1-interacting protein,and named it as GmBEHL1 because of the highest level of protein identity to BEH1(BES1/BZR1 homolog 1),a main player that mediates cross-talks between the BR and other signaling pathways in plants.So far,how BR is involved in nodulation remains elusive.Here,the results showed that GmBEHL1 interacts with NNC1 both in vitro and in vivo,and may act as a node to integrate BR and nodulation signaling pathways during soybean nodulation.GmBEHL1 is a negative regulator of soybean nodulation and has a similar role as BEH1 in regulating BR response and biosynthesis;Further studies showed that GmBEHL1 directly binds to the promoters of miR172 c and ENOD40-1,two key regulators in rhizobial infection and nodule organogenesis;lastly,this work proved the suppressive role of BR in nodule number but a positive role in nodule size.These results suggest that GmBEHL1-NNC1 interact with each other to integrate BR and nodulation signaling pathways to modulate nodule formation and development.The findings provide novel insights into further understanding of the regulatory mechanisms underlying plant hormonal regulation in root and nodule development.