Plant growth is greatly affected by environmental abiotic stresses, such as drought, high salinity, and low temperature. Therefore, plants have various response and defense systems in order to survive. The abiotic stresses induce various biochemical and physiologic responses in plants. The mechanisms of the molecular response to water stress in higher plants have been analyzed by studying a number of genes responding to drought, high salinity, and cold stresses at the transcriptional level (Bray, 1997; Hasegawa et al., 2000; Ingram and Bartels, 1996; Shinozaki and Yamaguchi-Shinozaki, 1997, 2000; Thomashow, 1999; Xiong and Zhu, 2002). The products of the stress-inducible genes can be classified into two groups: (i) those that function in directly protecting against environmental stresses; and (ii) those that regulate gene expression and signal transduction in the stress response (Bray, 1997; Hasegawa et al., 2000; Shinozaki and Yamaguchi-Shinozaki, 1997; Thomashow, 1999). Stress-inducible genes have been used to improve the stress tolerance of plants by gene manipulation. Hundreds of genes are thought to be involved in abiotic stress responses. Drought stress-inducible genes have been cloned, and their functions have been analyzed. Analysis of genes involved in the recovery from drought stress, as well as of drought-stress-inducible genes, is important not only to understand the molecular responses to abiotic stresses but also to improve the stress tolerance of crops by gene manipulation. Several physiologic studies on the recovery from drought stress have been reported (Bernacchia et al., 1996; Kranner et al., 2002; Navari-Izzo et al., 2000). However, other than the study on the ProDH (proline dehydrogenase) gene (Kiyosue et al., 1996), a gene encoding a key enzyme involved in proline degradation, there have been few reports on the expression of genes involved in the recovery from drought stress.
Recently, microarray technology has become a useful tool for the analysis of genome-scale gene expression (Eisen and Brown, 1999; Schena et al., 1995). cDNA sequences arrayed on a glass slide, at a density of up to 1000 genes cm−2, are hybridized simultaneously to a two-color fluorescently labeled cDNA probe pair prepared from RNA samples of different cell or tissue types, allowing direct and large-scale comparative analysis of gene expression. This technology, which uses expressed sequence tags (ESTs), was first demonstrated by analyzing 48 Arabidopsis genes for differential expression in roots and shoots (Schena et al., 1995). Reymond et al. (2000) analyzed the gene expression in response to mechanical wounding and insect feeding. Defense-signaling pathways have been analyzed using fungal pathogen and signaling molecules (Schenk et al., 2000).
Previously, we prepared an Arabidopsis full-length cDNA microarray using ca. 1300 full-length cDNAs and applied it to identify drought- or cold-inducible genes and target genes of DREB1A/CBF3, a transcription factor controlling stress-inducible gene expression (Seki et al., 2001a). Our previous results showed that the full-length cDNA microarray is useful in analyzing the expression pattern of Arabidopsis genes under drought and cold stresses, and in identifying target genes of stress-related transcription factors and potential cis-acting DNA elements by combining the expression data with the genomic sequence data. Recently, we prepared a new full-length cDNA microarray containing ca. 7000 independent full-length cDNA groups and applied it to identify new drought-, cold-, high-salinity-stress- or ABA-inducible genes (Seki et al., 2002b,c). In the present study, we applied the cDNA microarray to identify genes that are induced during the rehydration process after dehydration stress treatment, and analyzed the expression profiles of gene expression in the recovery from drought stress. We also examined differences in expression profiles between the recovery process from drought stress and drought stress response. This is the report on the systematic analysis of the expression profiles in the recovery from drought stress using microarrray technology. We also discuss the functions of the rehydration-inducible genes in stress response and tolerance.