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Phosphorylation of the Pseudomonas Effector AvrPtoB by Arabidopsis SnRK2.8 Is Required for Bacterial Virulence.

ABSTRACT: A critical component controlling bacterial virulence is the delivery of pathogen effectors into plant cells during infection. Effectors alter host metabolism and immunity for the benefit of pathogens. Multiple effectors are phosphorylated by host kinases, and this posttranslational modification is important for their activity. We sought to identify host kinases involved in effector phosphorylation. Multiple phosphorylated effector residues matched the proposed consensus motif for the plant calcium-dependent protein kinase (CDPK) and Snf1-related kinase (SnRK) superfamily. The conserved Pseudomonas effector AvrPtoB acts as an E3 ubiquitin ligase and promotes bacterial virulence. In this study, we identified a member of the Arabidopsis SnRK family, SnRK2.8, which interacts with AvrPtoB in yeast and in planta. We showed that SnRK2.8 was required for AvrPtoB virulence functions, including facilitating bacterial colonization, suppression of callose deposition, and targeting the plant defense regulator NPR1 and analyses receptor FLS2. Mass spectrometry analysis revealed that AvrPtoB phosphorylation occurs at multiple serine residues in planta, with S258 phosphorylation significantly reduced in the snrk2.8 knockout. AvrPtoB phospho-null mutants exhibited compromised virulence functions and were unable to suppress NPR1 accumulation, FLS2 accumulation, or inhibit FLS2-BAK1 complex formation upon flagellin perception. Taken together, these data identify a conserved plant kinase utilized by a pathogen effector to promote disease.

SUBMITTER: Lei L

PROVIDER: S-EPMC7808569 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Resistance to bacterial speck disease in tomato is activated by the physical interaction of the host Pto kinase with either of the sequence-dissimilar type III effector proteins AvrPto or AvrPtoB (HopAB2) from Pseudomonas syringae pv. tomato. Pto-mediated immunity requires Prf, a protein with a nucleotide-binding site and leucine-rich repeats. The N-terminal 307 amino acids of AvrPtoB were previously reported to interact with the Pto kinase, and we show here that this region (AvrPtoB(1-307)) is sufficient for eliciting Pto/Prf-dependent immunity against P. s. pv. tomato. AvrPtoB(1-307) was also found to be sufficient for a virulence activity that enhances ethylene production and increases growth of P. s. pv. tomato and severity of speck disease on susceptible tomato lines lacking either Pto or Prf. Moreover, we found that residues 308-387 of AvrPtoB are required for the previously reported ability of AvrPtoB to suppress pathogen-associated molecular patterns-induced basal defenses in Arabidopsis. Thus, the N-terminal region of AvrPtoB has two structurally distinct domains involved in different virulence-promoting mechanisms. Random and targeted mutagenesis identified five tightly clustered residues in AvrPtoB(1-307) that are required for interaction with Pto and for elicitation of immunity to P. s. pv. tomato. Mutation of one of the five clustered residues abolished the ethylene-associated virulence activity of AvrPtoB(1-307). However, individual mutations of the other four residues, despite abolishing interaction with Pto and avirulence activity, had no effect on AvrPtoB(1-307) virulence activity. None of these mutations affected the basal defense-suppressing activity of AvrPtoB(1-387). Based on sequence alignments, estimates of helical propensity, and the previously reported structure of AvrPto, we hypothesize that the Pto-interacting domains of AvrPto and AvrPtoB(1-307) have structural similarity. Together, these data support a model in which AvrPtoB(1-307) promotes ethylene-associated virulence by interaction not with Pto but with another unknown host protein.

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Phosphorylation of the Pseudomonas Effector AvrPtoB by Arabidopsis SnRK2.8 Is Required for Bacterial Virulence.

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