Indole-3-acetaldehyde dehydrogenase-dependent auxin synthesis contributes to virulence of Pseudomonas syringae strain DC3000

• Published in: PLoS pathogens Vol. 14; no. 1; p. e1006811
• Main Authors: McClerklin, Sheri A, Lee, Soon Goo, Harper, Christopher P, Nwumeh, Ron, Jez, Joseph M, Kunkel, Barbara N
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 02.01.2018; Public Library of Science (PLoS)
• Subjects: Acetaldehyde; Acetaldehyde dehydrogenase; Acetic acid; Aldehyde Oxidoreductases - chemistry; Aldehyde Oxidoreductases - genetics; Aldehyde Oxidoreductases - metabolism; Aldehyde Oxidoreductases - physiology; aldehydes; Amino acids; Analysis; Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis thaliana; Auxins; BASIC BIOLOGICAL SCIENCES; Binding Sites; Biochemical analysis; Biology; Biology and Life Sciences; Biosynthesis; Chemical synthesis; Cloning; Crystal structure; Dehydrogenase; Dehydrogenases; Funding; Gene Expression Regulation, Plant; Genes; Homology; Hormones; Host-Pathogen Interactions - genetics; Indoleacetic acid; Indoleacetic Acids - metabolism; Indoles - metabolism; Medicine and Health Sciences; Mutants; NAD; Organisms, Genetically Modified; Pathogenesis; Pathogenicity; Pathogens; Physical Sciences; Physiological aspects; Physiology; plant bacterial pathogens; Plant Diseases - genetics; Plant Diseases - microbiology; plant pathogens; Pseudomonas; Pseudomonas Infections - genetics; Pseudomonas Infections - microbiology; Pseudomonas syringae; Pseudomonas syringae - genetics; Pseudomonas syringae - metabolism; Pseudomonas syringae - pathogenicity; Research and Analysis Methods; Salicylic acid; Signaling; Substrate specificity; Substrates; Virulence; Virulence (Microbiology); Virulence - genetics; Virulence factors; United States > US; Missouri
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1006811

The bacterial pathogen Pseudomonas syringae modulates plant hormone signaling to promote infection and disease development. P. syringae uses several strategies to manipulate auxin physiology in Arabidopsis thaliana to promote pathogenesis, including its synthesis of indole-3-acetic acid (IAA), the predominant form of auxin in plants, and production of virulence factors that alter auxin responses in the host; however, the role of pathogen-derived auxin in P. syringae pathogenesis is not well understood. Here we demonstrate that P. syringae strain DC3000 produces IAA via a previously uncharacterized pathway and identify a novel indole-3-acetaldehyde dehydrogenase, AldA, that functions in IAA biosynthesis by catalyzing the NAD-dependent formation of IAA from indole-3-acetaldehyde (IAAld). Biochemical analysis and solving of the 1.9 Å resolution x-ray crystal structure reveal key features of AldA for IAA synthesis, including the molecular basis of substrate specificity. Disruption of aldA and a close homolog, aldB, lead to reduced IAA production in culture and reduced virulence on A. thaliana. We use these mutants to explore the mechanism by which pathogen-derived auxin contributes to virulence and show that IAA produced by DC3000 suppresses salicylic acid-mediated defenses in A. thaliana. Thus, auxin is a DC3000 virulence factor that promotes pathogenicity by suppressing host defenses.