Plant, Animal & Microbe Genomes X Conference Plant, Animal & Microbe Genomes X ConferenceJanuary 12-16, 2002
Town & Country Convention Center
San Diego, CA
Poster: Gene Isolation
The LjSym2 gene of Lotus japonicus is required for early developmental stages of the two root symbiosis found in legumes; the nitrogen-fixing root nodule symbiosis and arbuscular mycorrhiza. Phenotypic analysis suggests LjSym2 is a regulatory gene with a cell-type specific mode of action. Thus the cloned gene will provide molecular insights into early symbiotic signal transduction processes. Progeny of an interspecific cross (L. japonicus x L. filicaulis) as well as an intraspecific cross (L. japonicus ecotype Gifu x ecotype Miyakojima MG20) were screened in a bulk segregant approach for closely linked AFLP markers. BLASTN searches with sequences from converted AFLP markers and additional gene specific markers linked to LjSym2 resulted in a framework of homologous genes in Arabidopisis (At). These At genes mapped to a duplicated region on At chrII and At chrIV. To explore the degree of synteny between At and Lj in the LjSym2 region, we performed batch-BLASTN searches of all predicted cDNA sequences in a 4Mb window of the corresponding At chromosomes for highly homologous Lotus EST sequences. The resulting hits were further evaluated for the likely occurrence of multigene families and their duplication between At II and IV. Closely linked markers have been successfully generated based on alignments between Lj ESTs with At genomic sequences. A physical LjSym2 target contig of about 400kb has been assembled based on TAC library screening with cosegregating and closely linked flanking markers. In the context of the Lotus genome sequencing project, the entire contig has been completely sequenced, and the position of LjSym2 was physically delimited to less than 250kb on the TAC contig. Several candidate genes have been identified and have been tested by sequence comparison.