Indole-3-Acetaldehyde Dehydrogenase-dependent Auxin Synthesis Contributes to Virulence ofPseudomonas syringaeStrain DC3000

Abstract

22The bacterial pathogen Pseudomonas syringae modulates plant hormone signaling to promote 23 infection and disease development. P. syringae uses several strategies to manipulate auxin 24 physiology in Arabidopsis thaliana to promote pathogenesis, including synthesis of indole-3-25 acetic acid (IAA), the predominant form of auxin in plants, and production of virulence factors 26 that alter auxin responses in the host; however, the role of pathogen-derived auxin in P. syringae 27 pathogenesis is not well understood. Here we demonstrate that P. syringae strain DC3000 28 produces IAA via a previously uncharacterized pathway and identify a novel indole-3-29 acetaldehyde dehydrogenase, AldA, that functions in IAA biosynthesis by catalyzing the NAD-30 dependent formation of IAA from indole-3-acetaldehyde (IAAld). Biochemical analysis and 31 solving of the 1.9 Å resolution x-ray crystal structure reveal key features of AldA for IAA 32 synthesis, including the molecular basis of substrate specificity. Disruption of aldA and a close 33 homolog, aldB, lead to reduced IAA production in culture and reduced virulence on A. thaliana. 34We use these mutants to explore the mechanism by which pathogen-derived auxin contributes to 35 virulence and show that IAA produced by DC3000 suppresses salicylic acid-mediated defenses 36

Dual role of auxin in regulating plant defense and bacterial virulence gene expression duringPseudomonas syringae PtoDC3000 pathogenesis

“…Thus, introduction of the sid2-2 mutation restores normal levels of susceptibility to PtoDC3000 in GR-axr2-1 plants, suggesting that the reduced susceptibility in these plants with impaired auxin-signaling is due to elevated SAmediated defenses. This is consistent with previous observations suggesting that SA and auxin signaling are mutually antagonistic in P. syringae/Arabidopsis interactions (9)(10)(11).…”

NAD+ promotes assembly of the active tetramer of aldehyde dehydrogenase 7A1

“…Initial structural studies revealed ALDH7A1 forms a dimer‐of‐dimers tetramer both in crystallo and in solution . Many other ALDHs form the same tetramer, including ALDH1 , ALDH2 , ALDH5A1 , methylmalonate semialdehyde dehydrogenase , ALDH21 , 2‐aminomuconate‐6‐semialdehyde dehydrogenase , betaine aldehyde dehydrogenase , lactaldehyde dehydrogenase , indole‐3‐acetaldehyde dehydrogenase , α‐ketoglutarate‐semialdehyde dehydrogenase , propionaldehyde dehydrogenase , and salicylaldehyde dehydrogenase . Further investigation of the in‐solution oligomeric state of ALDH7A1 using analytical ultracentrifugation revealed a concentration‐dependent dimer–tetramer equilibrium with a dissociation constant ( K d ) of 16 μ m .…”

“…Many other ALDHs form the same tetramer, including ALDH1 [9][10][11][12], ALDH2 [13,14], ALDH5A1 [15], methylmalonate semialdehyde dehydrogenase [16], ALDH21 [17], 2-aminomuconate-6-semialdehyde dehydrogenase [18], betaine aldehyde dehydrogenase [19], lactaldehyde dehydrogenase [20], indole-3-acetaldehyde Abbreviations ALDH, aldehyde dehydrogenase; EM, electron microscopy; PDE, pyridoxine-dependent epilepsy; PLP, pyridoxal-5 0 -phosphate. dehydrogenase [21], a-ketoglutarate-semialdehyde dehydrogenase [22], propionaldehyde dehydrogenase [23], and salicylaldehyde dehydrogenase [24]. Further investigation of the in-solution oligomeric state of ALDH7A1 using analytical ultracentrifugation revealed a concentration-dependent dimer-tetramer equilibrium with a dissociation constant (K d ) of 16 lM [25].…”

Natural variation for unusual host responses and flagellin‐mediated immunity against Pseudomonas syringae in genetically diverse tomato accessions

“…Interestingly, we only observed gall formation when plants were spray‐inoculated in high humidity (as opposed to vacuum infiltrated). Because auxin is known to play a role in formation of galls on woody hosts (Glass & Kosuge, ) and is important for the virulence of DC3000 (Mutka et al ., ; Kunkel & Harper, ; McClerklin et al ., ), we investigated whether auxin plays a role in Pst stem gall formation. DC3000 strains with mutations in auxin biosynthetic genes still induced gall formation; however, these strains still produce some auxin as the ΔiaaL mutant only reduces lysine‐conjugated indole‐acetic acid (IAA) not free IAA (Glass & Kosuge, ), and the ΔaldAB double mutant still accumulates some auxin (McClerklin et al ., ).…”

“…Because Pst DC3000 produces auxin which plays a role in bacterial pathogenesis (Mutka et al, 2013;McClerklin et al, 2018) we hypothesized that this plant hormone might be involved in the formation of the stem galls as it is in other plant-pathogen interactions (Glass & Kosuge, 1986, 1988Mutka et al, 2013;McClerklin et al, 2018). We spray-inoculated five gall-forming accessions (LA1589, LA1242, LA1341, LA1521 and LA1578) with four different DC3000 strains that are reduced in indole-3-acidic acid (IAA) production: DC3000 DaldA, DC3000DaldB, DC3000DaldADaldB, and DC3000 DiaaL (Lam et al, 2014;McClerklin et al, 2018). No difference in gall formation was observed in plants inoculated with any of these strains compared to wildtype DC3000 (Fig.…”