| The first part of this research has been focused on studying the NBS-LRR family of resistance genes in M. truncatula. Sequences homologous to the NBS domain of NBS-LRR resistance genes were retrieved from M. truncatula. Phylogenetic analysis classified these sequences into TIR and non-TIR NBS subfamilies, and further subclassified them into several well-defined sequence clades within each subfamily. Comparative phylogenetic analysis of M. truncatula NBS sequences with those from several closely related legumes indicates a common ancestral origin that existed before speciation. Furthermore, phylogenetic distances among sequences from different legumes appear to be well correlated with established phylogenetic relationships among these legume species, suggesting a means of timing the development of various sequence groups relative to speciation events, Detailed genetic and physical mapping of both TIR and non-TIR NBS sequences in M. truncatula reveals several features of the genomic organization of this large gene family. First, most NBS sequences are organized as clusters, and few, if any, clusters contain both TIR and non-TIR sequences. Second, although most M. truncatula NBS sequences are organized as clusters of closely related sequences, examples were also found of mixed clusters containing sequences from distinct clades within the TIR or non-TIR subfamilies. Comparative mapping revealed several blocks of R gene loci that are syntenic between M. truncatula and soybean, and between M. truncatula and pea.; The second part of this research has been focused on the comparative genome analysis between M. truncatula and Arabidopsis . Our analysis reveals a lack of extended macrosynteny between the two genomes, despite local synteny over small genetic intervals. Complete sequencing and annotation of three M. truncatula BAC clones/contigs and comparisons of the predicted genes with their counterparts in Arabidopsis reveal networks of microsynteny between the two genomes. In all cases, however, the networks of synteny are degenerate, with conserved syntenic genes separated by non-syntenic genes both within and between species. Of 40 survey-sequenced M. truncatula BACs, about 50% of the cases reveal some level of microsynteny with one or more regions in Arabidopsis, indicating both conservation and divergence of local gene organization. |
