Postgenomic analysis of desiccation tolerance

Desiccation tolerance is the capacity to survive complete drying. It is an ancient trait that can be found in prokaryotes, fungi, primitive animals (often at the larval stages), whole plants, pollens and seeds. In the dry state, metabolism is suspended and the duration that anhydrobiotes can survive ranges from years to centuries. Whereas genes induced by drought stress have been successfully enumerated in tissues that are sensitive to cellular desiccation, we have little knowledge as to the adaptive role of these genes in establishing desiccation tolerance at the cellular level. This paper reviews postgenomic approaches in a variety of desiccation tolerant organisms in which the genetic responses have been investigated when they acquire the capacity of tolerating extremes of dehydration or when they are dry. Accumulation of non-reducing sugars, LEA proteins and a coordinated repression of metabolism appear to be the essential and universal attributes that can confer desiccation tolerance. The protective mechanisms of these attributes are described. Furthermore, it is most likely that other mechanisms have evolved since the function of about 30% of the genes involved in desiccation tolerance remains to be elucidated. The question of the overlap between desiccation tolerance and drought tolerance is briefly addressed.