Leguminous plants harbor nitrogen-fixing bacteria in specialized structures called root nodules. In this symbiotic relationship, the plants receive ammonia produced by the bacteria from atmospheric nitrogen as a nutrient, while in return providing the bacteria with products of photosynthesis. It is known that a protein called "NIN" regulates gene functions in a series of processes, from formation of root nodules, microbial infection into the nodules, and conversion of nitrogen into ammonia. However, it is still not well known how NIN acquired this mechanism.
A research team led by Professor Takuya Suzaki of the Institute of Life and Environmental Sciences at the University of Tsukuba performed experiments using legume Lotus japonicus (Miyakogusa). The team identified a short sequence of 15 amino acids immediately after the NIN region that binds to DNA sequences and named this region "FR." Based on protein-DNA interaction analysis and artificial intelligence (AI)-based prediction of protein structure, they revealed that FR plays a role in stabilizing DNA binding, enabling binding to various DNA sequences and thereby simultaneously regulating many genes required for root nodule symbiosis. Furthermore, evolutionary analysis indicated that this FR was present in some plants even before the emergence of root nodule symbiosis.
The study results showed a mechanism by which slight structural changes in proteins create new biological functions. In the future, the finding is expected to contribute to sustainable agriculture through the development of technologies that reduce dependence on nitrogen fertilizers and the artificial designing of symbiosis between plants and microbes.
(Article: Masanori Nakajo)
