Comparative Genomics of Filamentous Phages from Xanthomonas

• Main Authors: Ming-Ren Yen, 嚴明仁
• Other Authors: Yi-Hsiung Tseng
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/42138177638249238083

博士 === 國立中興大學 === 分子生物學研究所 === 91 === Several filamentous phages from Xanthomonas, including Lf, Xv, Xo, and Cflc, have previously been reported. In this study, two novel filamentous phages, Xv2 and Xo2, were isolated from Xanthomonas axonopodis pv. vesicatoria and Xanthomonas oryzae pv. oryzae, respectively. They are similar to other filamentous phages of Xanthomonas in having (i) restrictive host specificity, (ii) a single-stranded DNA genome, (iii) a replicative form (RF) as the intermediate during propagation, and (iv) a life cycle without lysis of host cells. Sequence determination revealed that the genome of Xv2 and Xo2 are 6,293 and 8,341 nt in size, respectively, containing seven genes on the viral strand which are corresponding to those of Lf, gII, gV, gVII, gVIII, gIII, gVI, and gI, which are defined as the core genes herein. In order to elucidate the phylogenetic relatedness, the six phages were analyzed with programs BLAST, CLUSTAL-X, TREEVIEW, TMHMM, Dot plot, and SignalP. Results indicated that the genome of filamentous phages of Xanthomonas consist of three different modules i.e., DNA replication module, structure module, and morphogenesis module. Each of the modules has its own high degree of conservation. Combination of different modules thus provides diversities and results in different phages. Data of phylogenetic analyses suggested that structure module and morphogenesis module are linked during the process of evolution, implicating that there is a direct contact between coat proteins and assembly proteins during morphogenesis. The ratio of size of the region containing core genes to that of the whole genome is almost the same among different phages, but the sizes of intergenic region (IR) vary. Several open reading frames are present in the IRs and two of them, encoding a 13-kDa and a 16-kDa protein, are found in all the filamentous phages. Based on sequence analysis, these two proteins are proposed to play important roles in phage replication. A novel mini plasmid pXV1.3, with a 1,313-bp genome consisting of a single gene (rep) encoding a replication protein, was discovered in X. axonopodis pv. vesicatoria Xvt146. In the presence of a filamentous Xanthomonas phage, pXV1.3 can be packaged and released into medium becoming transducing particles, which can infect the susceptible host cells.