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null (Ed.)Abstract Aldehyde dehydrogenases (ALDHs) catalyze the conversion of various aliphatic and aromatic aldehydes into corresponding carboxylic acids. Traditionally considered as housekeeping enzymes, new biochemical roles are being identified for members of ALDH family. Recent work showed that AldA from the plant pathogen Pseudomonas syringae strain PtoDC3000 (PtoDC3000) functions as an indole-3-acetaldehyde dehydrogenase for the synthesis of indole-3-acetic acid (IAA). IAA produced by AldA allows the pathogen to suppress salicylic acid-mediated defenses in the model plant Arabidopsis thaliana. Here we present a biochemical and structural analysis of the AldA indole-3-acetaldehyde dehydrogenase from PtoDC3000. Site-directed mutants targeting the catalytic residues Cys302 and Glu267 resulted in a loss of enzymatic activity. The X-ray crystal structure of the catalytically inactive AldA C302A mutant in complex with IAA and NAD+ showed the cofactor adopting a conformation that differs from the previously reported structure of AldA. These structures suggest that NAD+ undergoes a conformational change during the AldA reaction mechanism similar to that reported for human ALDH. Site-directed mutagenesis of the IAA binding site indicates that changes in the active site surface reduces AldA activity; however, substitution of Phe169 with a tryptophan altered the substrate selectivity of the mutant to prefer octanal. The present study highlights the inherent biochemical versatility of members of the ALDH enzyme superfamily in P. syringae.more » « less
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Abstract Plant development requires communication on many levels, including between cells and between organelles within a cell. For example, mitochondria and plastids have been proposed to be sensors of environmental stress and to coordinate their responses. Here we present evidence for communication between mitochondria and chloroplasts during leaf and root development, based on genetic and physical interactions between three
M echanosensitive channel ofS mall conductance‐L ike (MSL ) proteins fromArabidopsis thaliana .MSL proteins areArabidopsis homologs of the bacterialM echanos ensitivec hannel ofS mall conductance (MscS), which relieves cellular osmotic pressure to protect against lysis during hypoosmotic shock.MSL 1 localizes to the inner mitochondrial membrane, whileMSL 2 andMSL 3 localize to the inner plastid membrane and are required to maintain plastid osmotic homeostasis during normal growth and development. In this study, we characterized the phenotypic effect of a genetic lesion in , both in wild type and inMSL 1msl2 msl3 mutant backgrounds.msl1 single mutants appear wild type for all phenotypes examined. The characteristic leaf rumpling inmsl2 msl3 double mutants was exacerbated in themsl1 msl2 msl3 triple mutant. However, the introduction of themsl1 lesion into themsl2 msl3 mutant background suppressed othermsl2 msl3 mutant phenotypes, including ectopic callus formation, accumulation of superoxide and hydrogen peroxide in the shoot apical meristem, decreased root length, and reduced number of lateral roots. All these phenotypes could be recovered by molecular complementation with a transgene containing a wild type version of . In yeast‐based interaction studies,MSL 1MSL 1 interacted with itself, but not withMSL 2 orMSL 3. These results establish that the abnormalities observed inmsl2 msl3 double mutants is partially dependent on the presence of functionalMSL 1 and suggest a possible role for communication between plastid and mitochondria in seedling development.