Comprehensive analysis of gene expression in Nicotiana tabacum leaves acclimated to oxidative stress

Abstract

The molecular mechanisms by which plants acclimate to oxidative stress are poorly understood. To identify the processes involved in acclimation, we performed a comprehensive analysis of gene expression in Nicotiana tabacum leaves acclimated to oxidative stress. Combining mRNA differential display and cDNA array analysis, we estimated that at least 95 genes alter their expression in tobacco leaves acclimated to oxidative stress, of which 83% are induced and 17% repressed. Sequence analysis of 53 sequence tags revealed that, in addition to antioxidant genes, genes implicated in abiotic and biotic stress defenses, cellular protection and detoxification, energy and carbohydrate metabolism, de novo protein synthesis, and signal transduction showed altered expression. Expression of most of the genes was enhanced, except for genes associated with photosynthesis and light-regulated processes that were repressed. During acclimation, two distinct groups of coregulated genes (''early-'' and ''late-response'' gene regulons) were observed, indicating the presence of at least two different gene induction pathways. These two gene regulons also showed differential expression patterns on an oxidative stress challenge. Expression of ''late-response'' genes was augmented in the acclimated leaf tissues, whereas expression of ''early-response'' genes was not. Together, our data suggest that acclimation to oxidative stress is a highly complex process associated with broad gene expression adjustments. Moreover, our data indicate that in addition to defense gene induction, sensitization of plants for potentiated gene expression might be an important factor in oxidative stress acclimation. E xposure to sublethal biotic and abiotic stresses renders plants more tolerant to a subsequent, normally lethal, dose of the same stress, and this phenomenon is referred to as acclimation or acquired resistance (1-3). This induced stress resistance is not restricted to the same type of stress, and cross-tolerance between different stresses has been reported (4-6). Because many stress conditions provoke cellular redox imbalances, it has been suggested that oxidative stress defenses contribute to induced abiotic and biotic stress tolerance and are a central crosstolerance-mediating component (7). This notion is also supported by the fact that plants acclimated to heat or cold as well as plants showing acquired resistance to pathogens are all more tolerant to oxidative stress (8-10). Antioxidant defense responses have long been associated mainly with enhanced antioxidant enzyme activity and increased levels of antioxidant metabolites, such as ascorbic acid, glutathione, ␣-tocopherol, and carotenoids (11). More recently, induction of small heat shock proteins, the cellular protection gene glutatione Stransferase (GST), and the pathogenesis-related gene PR2 have also been associated with acquisition of oxidative stress tolerance (9,12,13).Acclimatory responses to various oxidants have been extensively studied in bacteria and yeast. In bacteria, at least 8...

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