Independent, Ongoing Clade-Specific Expansions of IS5 Elements in Pseudomonas syringae

Insertion Sequence (IS) elements are transposable regions of DNA which are present in a majority of bacterial genomes. It has been hypothesized that differences in distributions of IS elements across bacterial strains and species may reflect underlying differences in population biology. Therefore, shifts in IS element distributions between strains may be proxies for and reflective of changes in population dynamics. Here we investigate the presence and distribution of a subclass of IS5 elements throughout genomes of Pseudomonas syringae, by querying complete genomes for the presence of InsH (the main transposase found within these IS5 elements). We report that this one subclass of IS5 elements appears to have recently undergone multiple independent expansions in P. syringae clades and find that a majority of IS5 insertion sites are not conserved across three closely related P. syringae pv. lachrymans genomes. We present further evidence, as has been shown for other members of the IS5 family in different taxa, that elements from this IS5 subclass can drive the expression of downstream genes in P. syringae. Taken together, our results highlight how dynamic IS5 elements can be within and across P. syringae genomes and point toward the potential for IS5 elements to rewire the expression of the P. syringae chromosome.