Discovery of key genes involved in the symbiosis of legumes and rhizobia

March 2, 2020

The findings contribute to enhancing the efficient use of nitrogen fixation in root nodules

Legumes such as soybean can grow in nitrogen-poor soils, as they can use nitrogen in the air through the symbiotic relationship with rhizobia. It is expected that cultivation of legumes without relying on nitrogen fertilizers becomes possible by using this ability of rhizobia. Meanwhile, there are several strains of rhizobia with poor nitrogen-fixing ability, which barely fix nitrogen in the symbiotic conditions. These types of rhizobia often become dominate, thereby inhibiting symbiosis of those with high ability and limiting their symbiotic nitrogen fixing capability. This is a problem faced by present-day agriculture production.

A joint team of researchers from the National Agriculture and Food Research Organization (NARO), RIKEN CSRS, Nihon University, Tohoku University, and Kazusa DNA Research Institute used Lotus japonicus, a model legume plant, to analyze the genes involved in the symbiosis of rhizobia with poor-fixing ability. Two genes were found by analyzing an L. japonicus mutant and a rhizobial strain that can fix little nitrogen on this mutant: one gene in rhizobia that reduces nitrogen fixation (DCA1 gene), and another in L. japonicus that counteracts this effect and enables nitrogen fixation (APN1 gene).

This is the first evidence of a host plant’s symbiosis strategy in which it enables rhizobia strains not suitable for symbiosis to express normal nitrogen fixing activity. The findings may lead to improving the efficiency of symbiotic relationship between DCA1 gene-expressing rhizobia and legume plants, and lead to technological development that enhances efficient use of symbiotic nitrogen fixation.

Original article
Proceedings of the National Academy of Sciences doi:10.1073/pnas.1913349117
Y. Shimoda, Y. Nishigaya, H. Yamaya-Ito, N. Inagaki, Y. Umehara, H. Hirakawa, S. Sato, T. Yamazaki, M. Hayashi,
"The rhizobial autotransporter determines the symbiotic nitrogen fixation activity of Lotus japonicus in a host-specific manner".
Makoto Hayashi
Team Leader
Plant Symbiosis Research Team