Abstract
We tried to identify a novel gene involved in root nodule formation of Lotus japonicus, a model legume, by activation tagging. We introduced six tandem 35S enhancers to the genome of nod- castor mutant at random by the hairy root method with Agrobacterium rhizogenes. Among the resulting 4000 transformed lines, 8 plants formed root nodules. The enhancer tag was introduced only one of them, the others probably being somaclonal mutants. TAIR-PCR and inverse PCR analyses revealed the presence of a transcription factor-like gene near the tag. Using the genomic DNA fragment as a probe, we isolated a full-length clone and named the gene TOPAZ (for tag-associated object in putative activation zone). The TOPAZ promoter was fused with GUS gene and introduced into L. japonicus, and then the transformants were inoculated with Mesorhizobium loti. Strong GUS activity was detected at the basis of nodules, suggesting an important role of TOPAZ.
