A phytobacterial TIR domain effector manipulates NAD⁺ to promote virulence

Authors

Samuel Eastman, University of Nebraska-Lincoln
Thomas Smith, University of Nebraska-Lincoln
Mark A. Zaydman, Washington University School of Medicine
Panya Kim, University of Nebraska–LincolnFollow
Samuel Martinez, University of Nebraska-Lincoln
Neha Damaraju, Washington University in St Louis
Aaron DiAntonio, Washington University School of Medicine
Jeffrey Milbrandt, Washington University School of Medicine
Thomas E. Clemente, University of Nebraska - LincolnFollow
James R. Alfano, University of Nebraska-Lincoln
Ming Guo, University of Nebraska-Lincoln

Document Type

Article

Date of this Version

9-15-2021

Citation

New Phytologist (2022) 233: 890–904 doi: 10.1111/nph.17805

Comments

Open Access

Abstract

• The Pseudomonas syringae DC3000 type III effector HopAM1 suppresses plant immunity and contains a Toll/interleukin-1 receptor (TIR) domain homologous to immunity-related TIR domains of plant nucleotide-binding leucine-rich repeat receptors that hydrolyze nicotinamide adenine dinucleotide (NAD⁺) and activate immunity. In vitro and in vivo assays were conducted to determine if HopAM1 hydrolyzes NAD⁺ and if the activity is essential for HopAM1’s suppression of plant immunity and contribution to virulence.
• HPLC and LC-MS were utilized to analyze metabolites produced from NAD⁺ by HopAM1 in vitro and in both yeast and plants. Agrobacterium-mediated transient expression and in planta inoculation assays were performed to determine HopAM1’s intrinsic enzymatic activity and virulence contribution.
• HopAM1 is catalytically active and hydrolyzes NAD⁺ to produce nicotinamide and a novel cADPR variant (v2-cADPR). Expression of HopAM1 triggers cell death in yeast and plants dependent on the putative catalytic residue glutamic acid 191 (E191) within the TIR domain. Furthermore, HopAM1’s E191 residue is required to suppress both pattern-triggered immunity and effector-triggered immunity and promote P. syringae virulence.
• HopAM1 manipulates endogenous NAD⁺ to produce v2-cADPR and promote pathogenesis. This work suggests that HopAM1’s TIR domain possesses different catalytic specificity than other TIR domain-containing NAD+ hydrolases and that pathogens exploit this activity to sabotage NAD⁺ metabolism for immune suppression and virulence.