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

Abstract

Testing effector knockout strains of the Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) for reduced in planta growth in their native kiwifruit host revealed a number of nonredundant effectors that contribute to Psa3 virulence. Conversely, complementation in the weak kiwifruit pathogen P. syringae pv. actinidifoliorum (Pfm) for increased growth identified redundant Psa3 effectors.Psa3 effectors hopAZ1a and HopS2b and the entire exchangeable effector locus (DEEL; 10 effectors) were significant contributors to bacterial colonisation of the host and were additive in their effects on virulence. Four of the EEL effectors (HopD1a, AvrB2b, HopAW1a and HopD2a) redundantly contribute to virulence through suppression of pattern-triggered immunity (PTI).Important Psa3 effectors include several redundantly required effectors early in the infection process (HopZ5a, HopH1a, AvrPto1b, AvrRpm1a and HopF1e). These largely target the plant immunity hub, RIN4.This comprehensive effector profiling revealed that Psa3 carries robust effector redundancy for a large portion of its effectors, covering a few functions critical to disease.

NbPTR1confers resistance againstPseudomonas syringae pv. actinidiaein kiwifruit

“…It will be interesting to test in future work whether the interaction of the HopZ5:AcRIN4-2:NbPTR1a complex could be detected using a yeast three-hybrid system. Jayaraman et al 20 found that four out of five key redundant Psa3 effectors collectively essential for full Psa3 virulence probably targeted host RIN4 proteins (HopZ5a, AvrPto1b, AvrRpm1a, and HopF1e). Since only HopZ5 appears to be responsible for Nb PTR1a -conferred immunity against Psa3, this is probably further evidence that RIN4 itself may not be the host protein directly guarded by PTR1.…”

“…In soybean, RIN4 modification is involved in the recognition of AvrB and AvrRpm1 by Rpg1b and Rpg1r, respectively 19 . Recently, Jayaraman et al 20 found that five pathogenicity-associated Psa biovar 3 effectors (HopZ5a, HopH1a, AvrPto1b, AvrRpm1a, and HopF1e) are collectively essential for full Psa3 virulence and that they largely target host RIN4 proteins. Although most Psa T3Es have been identified, we have yet to fully uncover which NLR proteins are responsible for recognizing and responding to specific effectors during ETI.…”

Identification and characterization of innate immunity inActinidia melanandrain response toPseudomonas syringaepv.actinidiae

“…Callose deposit quantification assays were conducted and images acquired as previously described in Jayaraman et al (2023). Images were analysed using ImageJ software by determining the average area of a single callose deposit and then callose counts calculated based on total callose deposit area in each image.…”

“…The Psa3 V-13 complete effector knockout strain was generated using the pK18mobsacB-based vectors used previously to generate single knockout strains (Hemara et al, 2022; Jayaraman et al, 2023). The single effectors or effector blocks were sequentially knocked out to generate the 33 effector knockout strain (Psa3 V-13 Δ 33E ) in the order: hopZ5a/hopH1a ( using the hopZ5a/hopH1a double knockout vector ), hopBP1a ( previously hopZ3), hopQ1a, hopAS1b, avrPto1b ( previously avrPto5), avrRpm1a, fEEL (avrD1/avrB2b/hopF4a/hopAW1a/hopF1e/hopAF1b/hopD2a/hopF1a), hopF1c ( previously hopF2), hopD1a ( using the hopQ1a/hopD1a double knockout vector ), CEL (hopN1a/hopM1f/avrE1d), hopR1b, hopAZ1a, hopS2b, hopY1b, hopAM1a-1, hopAM1a-2, hopBN1a, hopW1c (previously hopAE1), hopAU1a, hopI1c , and hopAH1 block (hopAG1f/hopAH1c/hopAI1b ).…”

“…In Psa-resistant kiwiberry A. arguta versus Psa-susceptible A. chinensis , ETI and PTI responses can be affected by the presence or absence of avirulence and virulence Psa effectors (Hemara et al, 2022; Jayaraman et al, 2021, 2023). The molecular signatures underling these dynamically interconnected modes of host immunity can help identify pathways that are specifically activated and co-evolved in both compatible and incompatible kiwifruit-Psa interactions.…”