Sequence Diversity of rulA among Natural Isolates of Pseudomonas syringae and Effect on Function of rulAB -Mediated UV Radiation Tolerance

Abstract

The rulAB locus confers tolerance to UV radiation and is borne on plasmids of the pPT23A family in Pseudomonas syringae. We sequenced 14 rulA alleles from P. syringae strains representing seven pathovars and found sequence differences of 1 to 12% within pathovar syringae, and up to 15% differences between pathovars. Since the sequence variation within rulA was similar to that of P. syringae chromosomal alleles, we hypothesized that rulAB has evolved over a long time period in P. syringae. A phylogenetic analysis of the deduced amino acid sequences of rulA resulted in seven clusters. Strains from the same plant host grouped together in three cases; however, strains from different pathovars grouped together in two cases. In particular, the rulA alleles from P. syringae pv. lachrymans and P. syringae pv. pisi were grouped but were clearly distinct from the other sequenced alleles, suggesting the possibility of a recent interpathovar transfer. We constructed chimeric rulAB expression clones and found that the observed sequence differences resulted in significant differences in UV (wavelength) radiation sensitivity. Our results suggest that specific amino acid changes in RulA could alter UV radiation tolerance and the competitiveness of the P. syringae host in the phyllosphere.The pPT23A plasmid family encompasses the majority of native plasmids identified in the plant-pathogenic bacterium Pseudomonas syringae; these plasmids share a gene (repA) required for plasmid replication and, in most cases, additional areas of homology (16,30,35,38). pPT23A-type plasmids are diverse in size, and multiple plasmids sharing large regions of repeated sequences may be present in the same cell (3,8,30,35). Plasmids in the pPT23A family can encode determinants of importance in host-pathogen interactions such as the coronatine biosynthesis locus, which increases virulence, and the avirulence genes avrD, avrPphC, and avrPphF, which affect host range (1,21,46). Additional sequences known to be encoded on plasmids of the pPT23A family include the stbCBAD locus involved in plasmid stability (18), copper resistance determinants (6) and the streptomycin resistance transposon Tn5393 (39), and insertion sequence elements including IS51, IS801, IS870, and IS1240 (1, 18, 30). A common feature of all of these determinants is that functional loci encoding these traits are typically limited in distribution to small groups of P. syringae pathovars.Given the distribution of the pPT23A plasmid family throughout P. syringae pathovars, it is likely that these plasmids encode a "backbone" of traits of general importance to the P. syringae species. We are interested in the evolution of the pPT23A plasmid family in P. syringae, including determining the range of pathovars encompassed by particular plasmid lineages, characterizing genes encoded on these plasmids, and delineating the importance of horizontal transfer in pPT23A plasmid biology. In a previous study, we suggested that subgroups of pPT23A-like plasmids formed stable cohesive lineages as defined...

A DNA Polymerase V Homologue Encoded by TOL Plasmid pWW0 Confers Evolutionary Fitness on Pseudomonas putida under Conditions of Environmental Stress

“…These plasmids often carry multiple antibiotic resistance genes (75). The rulAB locus, which increases the survival of epiphytic P. syringae strains on leaf surfaces, is widely distributed among P. syringae virulence plasmids (59,60,80). The results presented in this study demonstrate that the catabolic TOL plasmid pWW0 carries the rulAB genes encoding a Pol V homologue.…”

“…Many plasmids possess the ability to increase the survival and mutation rates of their UV-irradiated bacterial host (22,25,32,33,35,38,50,53,(58)(59)(60)79). These phenotypes are connected with the presence of genes exhibiting homology to E. coli umuDC genes.…”

Comparison of the complete genome sequences of Pseudomonas syringae pv. syringae B728a and pv. tomato DC3000

“…Sequence variation within the rulA gene appears to have a significant impact upon UV tolerance of the host strain (21). A phylogenetic analysis of the rulA alleles found in different pseudomonads (Fig.…”

Comparative Genomic Analysis of the pPT23A Plasmid Family of Pseudomonas syringae

“…Plasmid-borne PAIs and effector gene clusters, along with mobile elements, have been found on several of these pPT23A family plasmids (PFPs) and have been demonstrated to play a role in the virulence of P. syringae (1,37,52,61). Besides effector proteins, PFPs have also been shown to encode other virulence and fitness determinants, including proteins conferring resistance to copper and antibiotics and tolerance to UV radiation, proteins involved in phytotoxin and hormone production, and chemotaxis transducer proteins (1,7,27,28,45,47,57,62,65,66,67). The role of PFPs in pathogen virulence and epiphytic and in planta bacterial growth has been demonstrated in a number of P. syringae pathosystems (37,52,67).…”