ALB1 of Lotus japonicus is Required for Infection Thread Formation

Abstract

Legumes establish symbiosis with rhizobia in root nodules. Recently, various symbiotic genes have been identified from model legumes to reveal molecular mechanisms of the symbiosis. We have isolated a symbiotic mutant, alb1 of Lotus japonicus Gifu B-129. When alb1 was infected with Mesorhizobium loti under nitrogen-starved conditions, it showed a serious growth inhibition phenotype compared with wild type. alb1 could form immature nodules, but they failed to develop mature nodules. In the wild type, numerous infected cells were developed in the central zone of nodules. However, no infected cells were observed in alb1. In alb1, infection threads were arrested in epidermal cells, and M. loti was not released to nodule cells. By map-based cloning followed by complementation of alb1 phenotype, it was revealed that ALB1 encoded a LRR-receptor like kinase.