A Functional Screen for the Type III (Hrp) Secretome of the Plant Pathogen <i>Pseudomonas syringae</i>

TLDR

Type III secreted effector proteins are key virulence factors but are difficult to identify. The study used an in vivo genetic screen to identify 13 Hrp‑secreted effectors in *Pseudomonas syringae*. An in vivo genetic screen targeting the Hrp type III secretion system was performed to uncover these effectors. The screen uncovered 13 effectors with conserved N‑terminal amino‑acid composition, enabled prediction of 38 effectors (15 novel), confirmed type III secretion for two, and revealed high interstrain variation suggesting host adaptation.

Abstract

Type III secreted “effector” proteins of bacterial pathogens play central roles in virulence, yet are notoriously difficult to identify. We used an in vivo genetic screen to identify 13 effectors secreted by the type III apparatus (called Hrp, for “hypersensitive response and pathogenicity”) of the plant pathogen Pseudomonas syringae . Although sharing little overall homology, the amino-terminal regions of these effectors had strikingly similar amino acid compositions. This feature facilitated the bioinformatic prediction of 38 P. syringae effectors, including 15 previously unknown proteins. The secretion of two of these putative effectors was shown to be type III–dependent. Effectors showed high interstrain variation, supporting a role for some effectors in adaptation to different hosts.