Abstract
During the legume-rhizobium symbiotic nitrogen fixation, rhizobia gain access to deeper cell layers via tubular plant-derived structures termed infection threads. The host plant tightly regulates symbiosis events such as the infection thread formation to maintain the normal symbiotic relation. To clarify the regulatory mechanism of infection thread formation, we performed some genetic analyses. We inoculated Lotus japonicus MG-20 'Miyakojima' and B-129 'Gifu' with GUS-labeled Mesorhizobium loti, which was followed by visualizing infection threads by X-Gluc staining, and found that the number of infection threads is different between the two accessions. QTL analysis using recombinant inbred lines between Miyakojima and Gifu showed a single peak in the chromosome 5 with the LOD score 3.3. The correlation coefficients between the infection thread trait and 13 agronomic traits of L. japonicus so far obtained suggested significant correlations with stem color, pod width and seed weight, respectively.
