Allelic Variants of the Pseudomonas syringae Type III Effector HopZ1 Are Differentially Recognized by Plant Resistance Systems

Abstract

The bacterial plant pathogen Pseudomonas syringae depends on the type III secretion system and type III-secreted effectors to cause disease in plants. HopZ is a diverse family of type III effectors widely distributed in P. syringae isolates. Among the HopZ homologs, HopZ1 is ancient to P. syringae and has been shown to be under strong positive selection driven by plant resistance-imposed selective pressure. Here, we characterized the virulence and avirulence functions of the three HopZ1 alleles in soybean and Nicotiana benthamiana. In soybean, HopZ1 alleles have distinct functions: HopZ1a triggers defense response, HopZ1b promotes bacterial growth, and HopZ1c has no observable effect. In N. benthamiana, HopZ1a and HopZ1b both induce plant defense responses. However, they appear to trigger different resistance pathways, evidenced by two major differences between HopZ1a- and HopZ1b-triggered hypersensitive response (HR): i) the putative N-acylation sites had no effect on HopZ1a-triggered cell death, whereas it greatly enhanced HopZ1b-triggered cell death; and ii) the HopZ1b-triggered HR, but not the HopZ1a-triggered HR, was suppressed by another HopZ homolog, HopZ3. We previously demonstrated that HopZ1a most resembled the ancestral allelic form of HopZ1; therefore, this new evidence suggested that differentiated resistance systems have evolved in plant hosts to adapt to HopZ1 diversification in P. syringae.

Oomycete pathogens encode RNA silencing suppressors

“…Soybean seeds ( G. max cultivar Williams 82) were pregerminated 31 and grown in growth pouches (Mega International) wetted with 10 ml of distilled water. The pouches were kept in a growth chamber with constant 22 °C, 90% humidity and a 16-h photoperiod.…”

The multilevel and dynamic interplay between plant and pathogen

“…The introduced of the HopZ alleles and homologues obtained their virulence function by escaping from a resistance protein recognition in hosts, which is not observed with the endogenous protein. 90,91 Perspective Although much consensus has been achieved in plant-pathogen interactions, the underlying mechanisms below are still poorly understood. PRRs have high specificity for PAMP recognition.…”

Bacterial Effector Activates Jasmonate Signaling by Directly Targeting JAZ Transcriptional Repressors

“…HopZ1b Pgy BR1 (HopZ1b in Pgy strain BR1; hereafter HopZ1b) promotes P. syringae multiplication in soybean; whereas the closely-related HopZ1a Psy A2 (HopZ1a in P. syringae pv. syringae strain A2; hereafter HopZ1a) triggers an HR in soybean cultivar Williams 82 and Arabidopsis thaliana accession Columbia-0 (Col-0, wild-type) [14]. HopZ1 mutants with the catalytic cysteine residues (C216 in HopZ1a or C212 in HopZ1b) substituted by alanines lose the virulence function or the HR-triggering activity, indicating that the functions of HopZ1 alleles require their enzymatic activities [9], [14].…”