syringae pv lachrymans str. M301315 (GenBank: AEAF01000091.1), P. syringae pv actinidiae str. M302091 (GenBank: AEAL01000073.1), P. syringae pv. morsprunorum str. M302280PT (GenBank: TPX-0005 cell line AEAE01000259.1)

and P. syringae Cit 7 (GenBank: AEAJ01000620.1). This T3SS-2 defines a distinct lineage in the Rhc T3SS family of at least the same evolutionary age as the split between the NGR234 T3SS-2 from the other rhizobial T3SSs. In light of these findings, there are two plausible scenarios. One is that P. syringae acquired the T3SS-2 cluster from an ancient donor which is common both to P. syringae and the Rhizobium sp. NGR234 T3SS-2, before the diversification of the P. syringae pathovars from each other, followed by subsequent loss from certain

members of the group. Another scenario is that multiple horizontal transfers from hypothetical donors into selected pathovars/strains occurred after their diversification. The present data set does not allow us to consider whether the hypothesis of an earlier acquisition followed by subsequent loss from members such as P. syringae pv tomato DC3000 might be considered more likely than several independent acquisitions. The genes hrc II N and hrc II V in P. syringae pv tabaci and P. syringae pv oryzae T3SS-2 clusters were split into at least two open reading frames in various positions suggesting possibly that they might be degenerate pseudogenes, while the hrc II C2 gene in P. syringae pv tabaci is further split in two ORFs as well (Figure 4). However, this is not the case for the P. syringae pv phaseolicola 1448a, P. syringae pv savastanoi and P. syringae click here pv aesculi T3SS-2 where all these genes remain intact while hrc Sirolimus mouse II C1 and hrc II N transcripts were observed in

P. syringae pv phaseolicola 1448a T3SS-2 case (Figure 4). Remarkably, the T3SS-2 genes expression was even higher in rich compared to minimal Bleomycin manufacturer medium (Figure 3). Minimal media of slightly acidic pH are thought to simulate in planta conditions and promote expression of the P. syringae T3SS-1 and effectors [24, 57, 58]. Such genes typically possess conserved motifs (hrp boxes) in their promoter regions and are transcriptionally controlled by the alternative sigma factor HrpL. However, the T3SS-2 operons in the P. syringae pv phaseolicola 1448a genome do not appear to have hrp boxes like those found in T3SS-1 genes of P. syringae strains [27]. This suggests that Psph 1448a does restrict T3SS-2 expression to in planta conditions and the potential contribution of the T3SS-2 in P. syringae life cycle may not be connected with the phytopathogenic potential of this species. Further functional studies are thus needed to reveal the exact biological roles of this secretion system in bacterium-plant interactions or other aspects of the bacterial life cycle. Suppression of other secretion systems under the T3SS-1 inducing conditions has also been reported for the T6SS of P. syringae pv syringae B728a [59] as well as for the P.