Abstract
Nitrogen-fixing symbiosis between legume plants and rhizobia is established on complex interactions between two symbiotic partners. To identify the host legume genes that play crucial roles in such interactions that are responsible in establishment of functional symbiosis, we isolated a Fix- mutant Ljsym105 from a model legume Lotus japonicus MG-20 regenerated from hypocotyl-derived calli after extensive in vitro culture. The Ljsym105 plants displayed nitrogen deficiency symptoms under symbiotic condition and formed small pale-pink nodules with acetylene reduction activity less than half of the wild type. Microscopic observations revealed that the Ljsym105 nodule infected cells underwent deterioration and/or degradation of the symbiosomes prematurely as well as disintegration of the whole infected cell cytoplasm. Genetic analysis revealed that Ljsym105 was monogenic and recessive, and genetic linkage analysis using DNA markers indicated that Ljsym105 locates on upper portion of chromosome 4 of Lotus japonicus. Map based cloning of Ljsym105 is in progress.
