Induction of the PDH bypass and upregulation of the ALDH7B4 in plants treated with herbicides inhibiting amino acid biosynthesis

- Imazamox and glyphosate provoke induction of the pyruvate dehydrogenase bypass and upregulation of ALDH7B4 expression.
- Analysis of pdc1-pdc2 mutant seedlings confirmed the role of ALDH7B4 in the PDH bypass.
- ALDH7B4 induction is not related with detoxification of the aldehydes or changes in lipid content or composition.
- ALDH7B4 upregulation partially alleviates the toxicity of herbicides on root growth, carbohydrate and organic acid content.

Imazamox and glyphosate represent two classes of herbicides that inhibit the activity of acetohydroxyacid synthase in the branched-chain amino acid biosynthesis pathway and the activity of 5-enolpyruvylshikimate-3-phosphate synthase in the aromatic amino acid biosynthesis pathway, respectively. However, it is still unclear how imazamox and glyphosate lead to plant death. Both herbicides inhibit amino-acid biosynthesis and were found to induce ethanol fermentation in plants, but an Arabidopsis mutant deficient in alcohol dehydrogenase 1 was neither more susceptible nor more resistant than the wild-type to the herbicides. In this study, we investigated the effects of the amino acid biosynthesis inhibitors, imazamox and glyphosate, on the pyruvate dehydrogenase bypass reaction and fatty acid metabolism in A. thaliana. We found that the pyruvate dehydrogenase bypass was upregulated following the treatment by the two herbicides. Our results suggest that the Arabidopsis aldehyde dehydrogenase 7B4 gene might be participating in the pyruvate dehydrogenase bypass reaction. We evaluated the potential role of the aldehyde dehydrogenase 7B4 upon herbicide treatment in the plant defence mechanism. Plants that overexpressed the ALDH7B4 gene accumulated less soluble sugars, starch, and fatty acids and grew better than the wild-type after herbicide treatment. We discuss how the upregulation of the ALDH7B4 alleviates the effects of the herbicides, potentially through the detoxification of the metabolites produced in the pyruvate dehydrogenase bypass.