Inventory of secreted proteins

The pathogenicity of Pseudomonas syringae pv tomato DC3000 depends on effector proteins that are injected into the host plant cell by the Hrp (hypersensitivity response and pathogenicity) type III protein secretion system. In the May 28 Proceedings of the National Academy of Sciences, Tanja Petnicki-Ocwieja and colleagues report an analysis of the DC3000 genome to identify new Hrp-dependent proteins (Proc Natl Acad Sci USA 2002, 99:7652-7657).

Petnicki-Ocwieja et al. found homologs of avirulence (Avr) proteins and potential effector candidates by mining the DC3000 genome for genes downstream of Hrp promoter sequences. Many of these proved to be secreted by the DC3000 Hrp system. In addition, comparative sequence analysis allowed them to predict Hrp-secreted proteins on the basis of export signal motifs. These two approaches led them to identify a number of novel Hops (Hrp-dependent outer proteins) that may be linked to pathogenicity.