5530). This is the first complete genome sequence for this species. Paired-end 454-pyrosequencing and primer walking on a fosmid library gave 3 contigs. The chromosome is 4.85 Mb with 65.6% GC ratio and 3,912 predicted CDS. Xap has a unique 41.2 kb plasmid with a 62.3% GC ratio and 45 CDS. Comparative genomics with other Xanthomonads was used to identify X. arboricola-specific genes indicating features relevant to differential host specificity and virulence mechanisms. Among those, composition and role of type III secretion system effectors repertoires was surveyed within all six X. arboricola pathovars. Applied
genomics has identified over 90 VNTR, several of which are currently being used to examine biodiversity and epidemiology of Xap and related pathovars, and design of improved diagnostics. This first complete genome sequence was also successfully used as a template to perform genomic assembly via mapping of short reads of several isolates from related pathovars. For example, the genome of a Xap isolate GBBC 2038 from the ornamental P. laurocerasus was assembled into 93 contigs. These two genomes show very high identity, the main difference being the presence of 10 kb genomic island in the ornamental isolate. Applied and comparative genomics improved our knowledge on host specificity and biodiversity of Xap, and allowed the development of efficient methods for detection of this plant disease. Overall, the availability of the first genome of X. arboricola constitutes a precious knowledge base for better comprehension of all other X. arboricola pathovars.