In plants, aldoximes per se act as defense compounds and are precursors of complex defense compounds such as cyanogenic glucosides and glucosinolates. Bacteria rarely produce aldoximes, but some are able to transform them by aldoxime dehydratase (Oxd), followed by nitrilase (NLase) or nitrile hydratase (NHase) catalyzed transformations. Oxds are often encoded together with NLases or NHases in a single operon, forming the aldoxime-nitrile pathway. Previous reviews have largely focused on the use of Oxds and NLases or NHases in organic synthesis. In contrast, the focus of this review is on the contribution of these enzymes to plant-bacteria interactions. Therefore, we summarize the substrate specificities of the enzymes for plant compounds. We also analyze the taxonomic and ecological distribution of the enzymes. In addition, we discuss their importance in selected plant symbionts. The data show that Oxds, NLases, and NHases are abundant in Actinobacteria and Proteobacteria. The enzymes seem to be important for breaking through plant defenses and utilizing oximes or nitriles as nutrients. They may also contribute, e.g., to the synthesis of the phytohormone indole-3-acetic acid. We conclude that the bacterial and plant metabolism of aldoximes and nitriles may interfere in several ways. However, further in vitro and in vivo studies are needed to better understand this underexplored aspect of plant-bacteria interactions.

Austrian Center of Industrial Biotechnology GmbH Krenngasse 37 A 8010 Graz Austria

Department of Genetics and Microbiology Faculty of Sciences Charles University Viničná 5 CZ 128 44 Prague Czech Republic

Faculty of Food and Biochemical Technology University of Chemistry and Technology Technická 5 CZ 166 28 Prague Czech Republic

Institute of Microbiology of the Czech Academy of Sciences Vídeňská 1083 CZ 142 20 Prague Czech Republic

Institute of Molecular Biotechnology Faculty of Technical Chemistry Chemical and Process Engineering Biotechnology Graz University of Technology Petersgasse 14 A 8010 Graz Austria

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Aldoxime dehydratases: production, immobilization, and use in multistep processes