Annual Report 2003

observed among the ribosomal protein genesand tRNA genes of rice, Arabidopsis andsugar beet. Transcription and post-transcriptionalmodification (RNA editing) in therice mitochondrial sequence were also examined.In all, 491 Cs in the genomic DNAwere converted to Ts in cDNA. The frequencyof RNA editing differed markedlydepending upon the ORF considered.Sequences derived from plastid and nucleargenomes make up 6.3% and 13.4% of themitochondrial genome, respectively. Thedegree of conservation of plastid sequencesin the mitochondrial genome ranged from61% to 100%, suggesting that sequencemigration has occurred very frequently.Three plastid DNA fragments that wereincorporated into the mitochondrial genomewere subsequently transferred to the nucleargenome. Nineteen fragments that were similarto transposon or retrotransposonsequences, but different from those found inthe mitochondrial genomes of dicots, wereidentified. The results indicate frequent andindependent DNA sequence flow to and fromthe mitochondrial genome during the evolutionof flowering plants, and this mayaccount for the range of genetic variationobserved among the mitochondrial genomesof higher plants.(http://rmg.rice.dna.affrc.go.jp/).Genome sequencing of Xanthomonasoryzae pv. oryzaeHirokazu Ochiai, Yasuhiro Inoue, Masaru Takeya,Hisatoshi KakuGenetic Diversity DepartmentBacterial blight of rice caused byXanthomonas oryzae pv. oryzae (Xoo) is oneof the most destructive diseases in rice growingcountries. This bacterium is known to bean ideal model for studying plant-microbeinteractions, race differentiation and evolutionof plant pathogens.In order to understand the molecularbasis of pathogenicity, therefore, genomesequencing of Xoo was conducted. The bacterialstrain used for the genome sequencingwas the Japanese representative race Istrain T7174 (MAFF 311018), which is registeredin the MAFF gene bank (NationalInstitute of Agrobiological Sciences: NIAS).Based on the sequence analysis, the totalgenome size was 4,938,844 bp with an averageGC content of 64%. The genome structureof Xoo was a single circular chromosome.No plasmid was detected. The numberof predicted genes on the genome was4,676, harboring two set of rRNA genes and53 tRNA genes. Acircular map of theXoo chromosome isshown in Fig. 1.The genome wasvery rich in genes forputative transposasehomologs, accountingfor approximately 8%of the total genomesize. In addition,many of these transposases,which werecomponents of inser-4.0Mb3.0MbXanthomonas oryzae pv. oryzaeMAFF 3110182.0MbFig. 1Circular map of Xanthomonas oryzae pv.oryzae MAFF 311018 chromosome.1.0MbAnnual Report 2003 7