Using T -DNA tagging to isolate novel genes from Arabidopsis essential for abiotic stress tolerance

Low temperature, drought and soil salinity are common adverse environmental conditions determining geographic distribution and productivity of land plants. To identify genetic loci that control stress tolerance in higher plants, large-scale mutant screens were carried out with a bialaphos marker-based T-DNA insertional collection of Arabidopsis thaliana plants. Genetic and molecular characterization of the recovered mutants revealed several novel genes and their encoded products. OSM1 (for osmotic stress-sensitive) locus encodes a plant syntaxin protein SYP61, which shows highest sequence similarity to mammalian syntaxins that are members of the SNARE superfamily of proteins required for vesicular/target membrane fusions. The recessive osm1 mutation renders increased sensitivity of osm1 plants to both ionic and osmotic stress. The stomata of osm1 plants were insensitive to both ABA-induced closing and inhibition of opening compared with wild-type plants. Together, our data implicate roles of OSM1/SYP61 in osmotic stress tolerance and in the ABA regulation of stomatal responses. Another gene HOS9 (for high expression of osmotically responsive genes) encodes a putative homeodomain transcription factor that is localized to the nucleus. The hos9-1 mutant plants are more sensitive to freezing both before and after cold acclimation. Most importantly, the expression of CBF transcription factor genes was not altered by the hos9-1 mutation. Expression profiling using Affimetrix near whole genome gene chip indicated that none of the genes controlled by HOS9 belong to the CBF regulon. We proposed that HOS9 mediates freezing tolerance through a novel pathway independent of CBF. Finally, the ENH1 (for enhancer of sos3-1) gene encodes a chloroplast-localized rubredoxin-like protein. enh1 mutations in wild-type background also cause increased salt sensitivity. The enh1-1 mutation enhances the salt sensitivity of sos3-1, but not sos2-1. The enh1-1 mutation also altered Na+ and K+ homeostasis and causes enhanced accumulation of superoxide under salt stress. enh1 and sos2-1 but not sos3-1 mutant plants show increased sensitivity to oxidative stress. Together, these results demonstrate that ENH1 play an important role in the detoxification of reactive oxygen species, and SOS2 but not SOS3 functions in the ENH1 pathway of salt tolerance