Enhanced symbiotic nitrogen fixation by Lotus japonicus containing an antisense β-1,3-glucanase gene

We hypothesized that root nodule formation would be promoted by lower expression of a b-1,3-glucanase gene (designated as LjGlu1), because expression of this gene is increased in transgenic Lotus japonicus that shows reduced nodulation. In order to suppress the expression of this gene, we introduced the antisense LjGlu1 gene into L. japonicus via Agrobacterium rhizogenes. Although there was no significant difference in shoot and root growth between L. japonicus possessing the antisense construct and plants containing an empty vector, the number of root nodules 28 days after inoculation with Mesorhizobium loti MAFF303099 increased in the antisense plant compared with the control plant. Moreover, the nitrogen fixation activity of the antisense plant was drastically enhanced. The mechanism of enhanced nitrogen fixation by suppression of the expression of LjGlu1 is unknown, but this phenomenon should be an important breeding target for leguminous plants. This is the first report of strong enhancement of nitrogen fixation activity by manipulation of a gene of the leguminous host plant.