Functional analysis of Sato, a drought stress responsive gene in potato and Arabidopsis.

Water deficit is one of the major limiting factors for crop productivity. Osmotic stress conditions affect many plant functions, including growth and development. Plants respond to stress signals by altering the expression of many genes, whose products have important reparative and protective functions. A previous transcriptome analysis (Ambrosone et al. 2006) indicated that distinctive changes in gene expression occurr during adaptation to long term water stress. Among the genes identified as up regulated we found the EST AW906734 coding for gene sato, acronimous of SAlt TOlerance. The EST AW906734, isolated from a potato stolon cDNA library, covers the 30% of the TC126154, composed by 9 EST with 90% of identity with a putative transcriptional factor of Vicia faba (GenBank O04273) and similarly to sato2 of B. vulgaris (AJ313093). Sato2 encode for a protein conferring salt resistance by complementation of a yeast defective mutant (Ros et al. unpublished) and contains a conserved RNA-binding protein domain. BlastP search reveals that the protein is highly conserved with more than 70% homology in several species as B. vulgaris, V. faba, S. olearia and A. thaliana. The expression of sato gene was confirmed to be regulated by water stress which induced 2, 6 and 10 fold increase of sato transcript level in potato cells, leaves and roots respectively. In order to get insights into the functional role of this gene in cellular response to osmotic stress, a preliminary characterization of the sato hortologous gene in Arabidopsis (Atsato, At4g16830) was carried out. At4g16830 is a nuclear RNA-binding protein of 355 aa containing a RGG box with unknown function and putatively localized in the nucleus and/or in the cytoplasm (www.arabidopsis.org). In Arabidopsis cells, sato was up-regulated by different stress treatments, in particular the expression was induced by 50 uM ABA, 150 mM NaCl and 10% PEG. A preliminary phenotypic analysis showed that seed germination of Atsato knock out (Atsato KO) was severely affected by ABA, NaCl and PEG treatments. Root elongation of Atsato KO was inhibited in presence of 0,2 uM ABA, 80 mM NaCl and in PEG treatments compared to wt Columbia (N60000) genotype. These results suggest a possible role of sato in ABA-mediated water stress response. The generation of sato overexpressing /RNAi plants, the promoter analysis and protein localization are in progress to establish the biological role of sato and its contribution to water stress tolerance.