The B-type response regulator GmRR11d mediates systemic inhibition of symbiotic nodulation

Key to the success of legumes is the ability to form and maintain optimal symbiotic nodules that enable them to balance the trade-off between symbiosis and plant growth. Cytokinin is essential for homeostatic regulation of nodulation, but the mechanism remains incompletely understood. Here, we show that a B-type response regulator GmRR11d mediates systemic inhibition of nodulation. GmRR11d is induced by rhizobia and low level cytokinin, and GmRR11d can suppress the transcriptional activity of GmNSP1 on GmNIN1a to inhibit soybean nodulation. GmRR11d positively regulates cytokinin response and its binding on the GmNIN1a promoter is enhanced by cytokinin. Intriguingly, rhizobial induction of GmRR11d and its function are dependent upon GmNARK that is a CLV1-like receptor kinase and inhibits nodule number in shoots. Thus, GmRR11d governs a transcriptional program associated with nodulation attenuation and cytokinin response activation essential for systemic regulation of nodulation. Cytokinin is essential for regulation of nodulation. Here, the authors identified a B-type response regulator GmRR11d that governs a transcriptional program associated with nodulation and cytokinin activation essential for systemic regulation of nodulation.

Automated summary

The success of legumes relies on the formation and maintenance of optimal symbiotic nodules, which require a balance between symbiosis and plant growth. Cytokinin plays a key role in the regulation of nodulation, but its mechanism is not fully understood. In this study, the authors identified a response regulator called GmRR11d that mediates the systemic inhibition of nodulation. GmRR11d is induced by rhizobia and low levels of cytokinin, and it can suppress the transcriptional activity of GmNSP1 on GmNIN1a, leading to the inhibition of soybean nodulation. GmRR11d positively regulates cytokinin response and its binding on the GmNIN1a promoter is enhanced by cytokinin. Furthermore, the induction of GmRR11d by rhizobia and its function are dependent on GmNARK, a CLV1-like receptor kinase that inhibits nodule formation in shoots. Overall, GmRR11d controls a transcriptional program associated with nodulation attenuation and cytokinin response activation, which is essential for systemic regulation of nodulation.