The wheat LEA protein Em functions as an osmoprotective molecule in Saccharomyces cerevisiae

The biased amino acid composition and aperiodic (random coil) configuration of Group 1 late embryogenesis-abundant (LEA) proteins imply that these proteins are capable of binding large amounts of water. While Group 1 LEAs have been predicted to contribute to osmotic stress protection in both embryonic and vegetative tissues, biochemical support has been lacking. We have used Saccharomyces cerevisiae as a model system to test the putative osmoprotective function of a wheat Group 1 LEA protein, Em. We demonstrate that expression of Em protein in yeast cells is not deleterious to growth in media of normal osmolarity and attenuates the growth inhibition normally observed in media of high osmolarity. Enhanced growth is observed in the presence of a variety of osmotically active compounds indicating that Em protein is capable of mitigating the detrimental effect of low water potential in a relatively non-specific manner. These results are the first biochemical demonstration of an osmoprotective function for a Group 1 LEA and suggest that the yeast expression system will be useful in dissecting the mechanism of protection through structure-function studies.