Differential gene regulation in potato cells and plants upon abrupt or gradual exposure to water stress.

Potato cDNA microarray slides (TIGR 1 K) were used to compare changes in gene expression of two potato cell populations subjected to shock or gradual exposure to PEG-mediated water stress. A total of 180 transcripts were found to be statistically up- or down-regulated in PEG-shocked or gradually stressed cells, compared to untreated control cells. Up-regulated genes in shocked cells were prevalently involved in carbohydrate metabolism, cellular communication, and signal transduction. In cells stressed gradually, the most represented induced genes were those involved in signal transduction, in response to environmental signals and in the regulation of transcription and translation machineries, including the heat shock protein 90-2, ribosomal and RNA-binding proteins. The expression of selected up-regulated genes was also tested in potato plants subjected to slow soil-drying conditions. Interestingly, the rgga gene, encoding an RNA-binding protein, was strongly induced in both leaves and roots of water-stressed potato plants, supporting its putative function in adaptive mechanisms to water stress. Pointing to differences in gene expression between shock-like and adaptive response, our findings might contribute to the controversial debate on the biological function of stress-responsive genes in cell damage repair or in restoring homeostasis and elaborating longer term responses for adaptation.