A Selaginella lepidophylla trehalose-6-phosphate synthase complements growth and stress-tolerance defects in a yeast tps1 mutant

The accumulation of the disaccharide trehalose in anhydrobiotic organisms a llows them to survive severe environmental stress. A plant cDNA, SlTPS1, en coding a 109-kD protein, was isolated from the resurrection plant Selaginel la lepidophylla, which accumulates high levels of trehalose. Protein-sequen ce comparison showed that SlTPS1 shares high similarity to trehalose-6-phos phate synthase genes from prokaryotes and eukaryotes. SlTPS1 mRNA was const itutively expressed in S. lepidophylla. DNA gel-blot analysis indicated tha t SlTPS1 is present as a single-copy gene. Transformation of a Saccharomyce s cerevisiae tps1 Delta mutant disrupted in the ScTPS1 gene with S. lepidop hylla SlTPS1 restored growth on fermentable sugars and the synthesis of tre halose at high levels. Moreover, the SlTPS1 gene introduced into the tps1 D elta mutant was able to complement both deficiencies: sensitivity to sublet hal heat treatment at 39 degrees C and induced thermotolerance at 50 degree s C. The osmosensitive phenotype of the yeast tps1 Delta mutant grown in Na Cl and sorbitol was also restored by the SlTPS1 gene. Thus, SITPS1 protein is a functional plant homolog capable of sustaining trehalose biosynthesis and could play a major role in stress tolerance in S. lepidophylla.