Genes Controlling Calcium-Enhanced Tolerance to Salinity in Plants

The specific objectives of the proposed research were to identify, clone and characterize downstream cellular target(s) of SOS3 in Arabidopsis thaliana, to analyze the Ca2+-binding characteristics of SOS3 and the sos3-1 mutant and their interactions with SOS3 cellular targets to analyze the SOS3 cell-specific expression patterns, and its subcellular localization, and to assess the in vivo role of SOS3 target protein(s) in plant tolerance to salinity stress. In the course of the study, in view of recent opportunities in identifying Ca2+ - responsive genes using microarrays, the group at Weizmann has moved into identifying Ca2+-responsive stress genes by using a combination of aqeuorin-based measurements of cytosolic Ca and analysis by DNA microarrays of early Ca-responsive genes at the whole genome level. Analysis of SOS3 (University of Arizona) revealed its expression in both roots and shoots. However, the expression of this gene is not induced by stress. This is reminiscent of other stress proteins that are regulated by post-transcriptional mechanisms such as the activation by second messengers like Ca. Further analysis of the expression of the gene using promoter - GUS fusions revealed expression in lateral root primordial. Studies at the Weizmann Institute identified a large number of genes whose expression is up-regulated by a specific cytosolic Ca burst evoked by CaM antagonists. Fewer genes were found to be down-regulated by the Ca burst. Among the up-regulated genes many are associated with early stress responses. Moreover, this study revealed a large number of newly identified Ca-responsive genes. These genes could be useful to investigate yet unknown Ca-responsive gene networks involved in plant response to stress.