A full set of disease resistance(R) candidate genes encoding nucleotide-binding sites(NBS) in a complete genome of Populus trichocarpa was identified and characterized by structural diversities,physical positions,phylogenetic relationships.Based on structures of N-terminal motif and leucine-rich repeat domains motif,we found 381 NBS-coding sequences with 122 non-regular NBS genes and 259 regular NBS genes that were further classified into 13 types such as TNL,CNL,NL,XNL,TN and other minor types.Meanwhile 81.9% of the NBS genes were distributed in cluster,and 81.8% of the cluster genes had duplicates.The results showed that there were many duplicate phenomenon occurred in the evolution of disease resistance genes of P.trichocarpa.After analysis of NBS standard phylogenetic tree in the genome of P.trichocarpa,the structure of tree exhibited a star topology,and the regular NBS genes were classified into 68 groups by less than 30% amino acid sequence diversity in each domain.
