DEHYDRINS - DESSICATION PROTECTION PROTEINS OF PLANTS

Abstract

Dehydrins (DHN) are a family of proteins which belong to a larger group of late embryogenesis abundant (LEA) proteins known as D 11 or LEA group II . They are expressed in seed cell tissues in late stage of seed maturation and in vegetative tissues during normal conditions and in response to stresses which lead to cellular dehydration. The specific structural features of DHN are the conserved K, Sand Y segments. The K-segment, which is the distinctive feature of all DHN, is the most conserved lysine-rich amino acid sequence (EKKGIMDKIKEKLPG) present near the C-terminus. The S segment with a track of serine residues and the Y segment with a sequence TNDEYGNP are less conserved. Another segment - the q segment is rich in polar amino acids. Based on the presence of the K, Sand Y segments, DHN are classified into 5 sub-classes, namely, Y nSKn. Y nKn. SKn. Kn and KnS. DHN are present in higher plants, algae, yeasts, and cyanobacteria. Moreover, they are localized in various cell compartments. such as, cytosol, nucleus, mitochondria and vacuoles. Several DHN genes in different chromosomes have been cloned, characterized and mapped. In addition, many specific short sequences '(Cis-elements) in the promoter have been recognized by specific transcription factors induced by abscisic acid or low temperature. The true functions of DHN are yet to be conclusively established. However, in vitro, studies show some (YSKo-type) bind to lipid vesicle, and others (KoS-type) which seem to bind to some metallic elements have the ability to scavenge reactive oxygen species. Moreover, there are indications that the SKn- and Kn-type playa crucial role in cold acclimation process.