ABSTRACT
Members
of the pPT23A plasmid family of Pseudomonas syringae play an
important role in the interaction of this bacterial pathogen with host
plants. Complete sequence analysis of several pPT23A family plasmids
(PFPs) has provided a glimpse of the gene content and virulence
function of these plasmids. We constructed a macroarray containing 161
genes to estimate and compare the gene contents of 23 newly analyzed
and eight known PFPs from 12 pathovars of P. syringae, which
belong to four genomospecies. Hybridization results revealed that PFPs
could be distinguished by the type IV secretion system (T4SS) encoded
and separated into four groups. Twelve PFPs along with pPSR1 from
P. syringae pv. syringae, pPh1448B from P. syringae
pv. phaseolicola, and pPMA4326A from P. syringae pv.
maculicola encoded a type IVA T4SS (VirB-VirD4 conjugative system),
whereas 10 PFPs along with pDC3000A and pDC3000B from P.
syringae pv. tomato encoded a type IVB T4SS (tra system).
Two plasmids encoded both T4SSs, whereas six other plasmids carried
none or only a few genes of either the type IVA or type IVB secretion
system. Most PFPs hybridized to more than one putative type III
secretion system effector gene and to a variety of additional genes
encoding known P. syringae virulence factors. The overall gene
contents of individual PFPs were more similar among plasmids within
each of the four groups based on T4SS genes; however, a number of
genes, encoding plasmid-specific functions or hypothetical proteins,
were shared among plasmids from different T4SS groups. The only gene
shared by all PFPs in this study was the repA gene, which
encoded sequences with 87 to 99% amino acid identityamong 25 sequences examined. We proposed a model to illustrate the
evolution and gene acquisition of the pPT23A plasmid family. To our
knowledge, this is the first such attempt to conduct a global genetic
analysis of this important plasmid
family.
Complete sequence and comparative genomic analysis of eight native Pseudomonas syringae plasmids belonging to the pPT23A family
