Proteins Required for Desiccation Tolerance
LEA protein sequences are highly conserved among a wide variety of species. They are related to two other groups of proteins, the RAB (responsive to ABA) and DHN (dehydrin) proteins. These protein classes accumulate in a variety of tissues experiencing cellular dehydration, e.g. maturing embryos and pollen, and vegetative tissues exposed to drought stress, including extreme desiccation of "resurrection plants" (Craterostigma plantagineum). The LEA, RAB, and DHN proteins are all water soluble, basic, rich in glycine and lysine, and low in hydrophobic residues. As a result they are extremely hydrophilic and stable to boiling. These features led Dure and colleagues (1989) to propose that they function specifically in the protection of membranes and proteins against desiccation damage, possibly by binding water tightly or providing hydrophilic interactions in the absence of free water, and by preventing crystallization of cellular components through their ability to act as stabilizing "solvents," similar to the effects of sugars. One of these proteins confers increased osmotolerance in transgenic yeast (Swire-Clark and Marcotte 1999).