Pseudomonas syringae effector HopZ3 suppresses the bacterial AvrPto1–tomato PTO immune complex via acetylation

Abstract

The plant pathogen Pseudomonas syringae secretes multiple effectors that modulate plant defenses. Some effectors trigger defenses due to specific recognition by plant immune complexes, whereas others can suppress the resulting immune responses. The HopZ3 effector of P. syringae pv. syringae B728a (PsyB728a) is an acetyltransferase that modifies not only components of plant immune complexes, but also the Psy effectors that activate these complexes. In Arabidopsis, HopZ3 acetylates the host RPM1 complex and the Psy effectors AvrRpm1 and AvrB3. This study focuses on the role of HopZ3 during tomato infection. In Psy-resistant tomato, the main immune complex includes PRF and PTO, a RIPK-family kinase that recognizes the AvrPto effector. HopZ3 acts as a virulence factor on tomato by suppressing AvrPto1Psy-triggered immunity. HopZ3 acetylates AvrPto1Psy and the host proteins PTO, SlRIPK and SlRIN4s. Biochemical reconstruction and site-directed mutagenesis experiments suggest that acetylation acts in multiple ways to suppress immune signaling in tomato. First, acetylation disrupts the critical AvrPto1Psy-PTO interaction needed to initiate the immune response. Unmodified residues at the binding interface of both proteins and at other residues needed for binding are acetylated. Second, acetylation occurs at residues important for AvrPto1Psy function but not for binding to PTO. Finally, acetylation reduces specific phosphorylations needed for promoting the immune-inducing activity of HopZ3’s targets such as AvrPto1Psy and PTO. In some cases, acetylation competes with phosphorylation. HopZ3-mediated acetylation suppresses the kinase activity of SlRIPK and the phosphorylation of its SlRIN4 substrate previously implicated in PTO-signaling. Thus, HopZ3 disrupts the functions of multiple immune components and the effectors that trigger them, leading to increased susceptibility to infection. Finally, mass spectrometry used to map specific acetylated residues confirmed HopZ3’s unusual capacity to modify histidine in addition to serine, threonine and lysine residues.

Contrasting effector profiles between bacterial colonisers of kiwifruit reveal redundant roles converging on PTI‐suppression and RIN4

“…Three out of these five putatively redundant effectors in Psa3, or their orthologs in other plant–pathogen systems, have recently been shown to target the plant immunity hub RIN4 (Yoon & Rikkerink, 2020; Choi et al ., 2021; Jeleńska et al ., 2021). HopF1e and HopH1 have not been characterised for their in planta targets, but HopF1e is part of the larger HopF family that has members known to interact with RIN4 (Lo et al ., 2017).…”

Metaeffector interactions modulate the type III effector-triggered immunity load of Pseudomonas syringae

“…Further functional characterization will be required to clarify the mechanisms of both AvrPto1m and HopT1b suppression. This may occur through manipulation of the ETI-eliciting T3SE, the ETI-signaling pathways, or both as observed for the ETI-suppressor HopZ3 [ 72 , 73 ].…”

Contrasting effector profiles between bacterial colonisers of kiwifruit reveal redundant roles and interplay converging on PTI-suppression and RIN4

“…In our current work, three out of the other four of these redundant virulence-associated effectors were shown to directly interact with AcRIN4 orthologs, suggesting a mechanism of virulence conserved in Psa3. This latter screen also tested all Psa3 effectors that are part of the HopF family (HopBN1a, HopF4a, HopF1c, and HopF1e), which has members known to target RIN4 as well as other orthologs that have been shown to target RIN4 (Wilton et al ., 2010; Lo et al ., 2017; Choi et al ., 2021; Jeleńska et al ., 2021). Several of these effectors showed interesting relationships between their ability to target AcRIN4 and their contribution to pathogenicity.…”

“…The quadruple and quintuple mutants were also considerably reduced in virulence (Figure 6C). Three out of these five putatively redundant effectors in Psa3, or their orthologs in other plantpathogen systems, have recently been shown to target the plant immunity hub RIN4 (Yoon & Rikkerink, 2020;Choi et al, 2021;Jeleńska et al, 2021). HopF1e and HopH1 have not been characterised for their in planta targets, but HopF1e is part of the larger HopF family that has members known to interact with RIN4 (Lo et al, 2017).…”