Selective and powerful stress gene expression in Arabidopsis in response to malondialdehyde

Abstract

Summary: The provenance, half‐life and biological activity of malondialdehyde (MDA) were investigated in Arabidopsis thaliana. We provide genetic confirmation of the hypothesis that MDA originates from fatty acids containing more than two methylene‐linked double bonds, showing that tri‐unsaturated fatty acids are the in vivo source of up to 75% of MDA. The abundance of the combined pool of free and reversibly bound MDA did not change dramatically in stress, although a significant increase in the free MDA pool under oxidative conditions was observed. The half‐life of infiltrated MDA indicated rapid metabolic turnover/sequestration. Exposure of plants to low levels of MDA using a recently developed protocol powerfully upregulated many genes on a cDNA microarray with a bias towards those implicated in abiotic/environmental stress (e.g. ROF1 and XERO2). Remarkably, and in contrast to the activities of other reactive electrophile species (i.e. small vinyl ketones), none of the pathogenesis‐related (PR) genes tested responded to MDA. The use of structural mimics of MDA isomers suggested that the propensity of the molecule to act as a cross‐linking/modifying reagent might contribute to the activation of gene expression. Changes in the concentration/localisation of unbound MDA in vivo could strongly affect stress‐related transcription.