Abstract
Development of infection threads is one of the unique features in symbiosis between legume plants and rhizobia. In Lotus japonicus, broad infection threads are formed in root hairs that ramify into several fine infection threads after penetrating into the cortical cells to form the infection thread network. One of the Lotus mutants, crinkle, develops bumps after inoculation with Mesorhizobium loti. The infection threads are aborted before ramification, and aggregates of bacteria can be observed inside the bumps. Another mutant, alb1, shows a different type of abortion, which is, the infection threads are formed in the trichoblast-like root hairs, and swell to occupy full volume of root hairs. Those phenotypes observed in mutants are also typical in wild type plants, so that the genes responsible for mutants have crucial roles for regulating infection events in Lotus.
