Lotus japonicus FEN1 protein play an essential role in successful symbiotic nitrogen fixation

Abstract

Most of rhizobia are able to fix N₂ only when they inhabit in the compatible host legume nodule cells and differentiate into bacteroids. This indicates that N₂ fixing activity of rhizobia is strictly controlled by interactions with host legume plants. However, it is unclear how the host plants regulate nitrogenase activity of rhizobia in the nodules.
A Lotus japonicus Fix^- mutant, fen1, forms small and pale pink nodules. Acetylene reduction activity of the fen1 nodules is very low, though rhizobia infected in the nodule cells appeared to differentiate into bacteroids. Therefore, Fen1 gene is presumed to be essential for controlling nitrogenase activity of rhizobia. We identified the Fen1 gene by map-based cloning and complementation test. Here we report a possible function of FEN1 protein in the development of N₂ fixing activity, based on the results of functional analysis of recombinant protein in Saccharomyces.