Annual Report 2003

tion sequences (ISs), were located nearstrain-specific genes with altered codonusage and GC content, suggesting that thesegenes may have been acquired through lateraltransfer.Of the genes related to pathogenicity ofplant-pathogenic bacteria, hrp is one of themost important genes. A cluster of hrpgenes encoding a type III secretion system(TTSS) is essential for pathogenicity. Wefound three novel genes specific to Xoo in thehrp cluster. These genes were regulated byHrpX, which is the activator of the hrpgenes. It was very notable that many of thetransposases were distributed around thehrp gene cluster. Avr genes, which are fundamentalto development or restriction of thedisease, were also found in the Xoo genome.Sixteen copies of avr/pth members were scatteredrandomly in the Xoo genome. Thesewere distributed in different genomic loci,and 2 or 3 avr genes were repeated in tandem,and transposases or phage-relatedgenes were located neighboring them. Thus,these multiple copies of avr genes in onegenome appear to be related to race specializationof Xoo.The genome sequencing of Xoo may be abreakthrough in the understanding of themolecular genetics of the bacterium and themolecular interaction with the host riceplant.Molecular phylogenetic analysis helpsdefine a new taxonomic system forthe Asian VignaNorihiko Tomooka, Akito Kaga,Duncan VaughanGenetic Diversity DepartmentFig. 1Diversity of a genus Vigna subgenus Ceratotropis representative speciescollection based on AFLP analysis.The Asian Vigna (genus Vigna subgenusCeratotropis) includes economically importantfood legumes such as mungbean, blackgram,rice bean and azuki bean. Wild relativesof these crops are important generesources for future breeding. However, theAsian Vigna species are difficult to distinguish,thus molecular analyses combinedwith morphological studies have been conducted,and these have led to a new taxonomicsystem for this subgenus.As a result of many years of collecting, acomprehensive germplasm collection of theAsian Vigna has been assembled at NIAS.Based on various data a representative set ofaccessions (species standard collection) thatencompasses the diversity in this germplasmcollection was selected and has been analyzedby various techniques including AFLP(Fig. 1), rDNA ITS and cpDNA atpB-rbcLspacer region sequencing. The results of8 Annual Report 2003