Function of the wheat TaSIP gene in enhancing drought and salt tolerance in transgenic Arabidopsis and rice

Microarray analysis of a salt-tolerant wheat mutant identified a gene of unknown function that was induced by exposure to high levels of salt and subsequently denoted TaSIP (Triticum aestivum salt-induced protein). Quantitative PCR analysis revealed that TaSIP expression was induced not only by salt, but also by drought, abscisic acid (ABA), and other environmental stress factors. Transgenic rice plants that expressed an RNA interference construct specific for a rice gene homologous to TaSIP was more susceptible to salt stress than wild-type rice plants. Subcellular localization studies showed that the TaSIP localized to the cell membrane. Under conditions of salt and drought stress, transgenic Arabidopsis plants that overexpressed TaSIP showed superior physiological properties compared with control plants, including lower Na⁺ content and upregulation of several stress resistance genes. Staining of transgenic tissues with β-glucuronidase (GUS) failed to indicate tissue-specific activity of the full-length TaSIP promoter. Quantitative analysis of GUS fluorescence in transgenic plants treated with ABA or salt stress revealed that the region 1,176–1,410 bp from the start codon contained an ABA-responsive element and that the region 579–1,176 bp from the start codon upstream of the exon contained a salt-stress-responsive element. Based on these results, we conclude that the key part of the TaSIP gene is the region of its promoter involved in salt tolerance.