T-DNA tagging of nodulation- and root-related genes in Lotus japonicus: Expression patterns and potential for promoter trapping and insertional mutagenesis

High-efficiency transformation of the autogamous diploid legume Lotus japon icus by means of Agrobacterium rhizogenes was used to develop plant lines e xpressing a promoter-less gusA gene in a nodulation- or lateral root-associ ated manner. The approach exploits the putatively preferential integration of T-DNA into actively transcribed regions, thereby providing an enrichment for gene tagging events associated with the quickly assayable activation o f a gusA promoter-less construct. Taking advantage of this enrichment and s election strategy, a T-DNA tagging program was initiated and screening for P-glucuronidase (GUS) activity was performed on root clones isolated after transformation with a gusA-promoter-less binary vector. The aim of this app roach is the identification of genes involved in nodule formation induced b y Mesorhizobium loti lateral root organogenesis, and the eventual isolation of corresponding mutants. A large collection (220) of GUS-positive transfo rmants showing a variety of expression patterns in different regions of roo ts and nodules was obtained; a preliminary molecular characterization of th ese plants is presented.