CLONING OF TWO DEHYDRIN GENES FROM THE HALOPHYTES OF THE EGYPTIAN NORTHWEST COASTAL REGION

Abstract

Throughout their life cycle, plants are subjected to many adverse environmental stresses such as drought, high temperatures, etc. that dramatically affect plant survival and reduce productivity. To cope with such stresses, plants produce several stress-induced proteins that play a definite role in protecting plants during such severe conditions (Muthalif and Rowland, 1994). The late embryonic stage represents one of the abiotic stress conditions where the seed starts to lose water content during desiccation. Several molecules have been found to play vital roles in seed development and are thought to help in saving the embryos during desiccation. These include sugars (Koster and Leopold, 1988; Chen and Burris, 1990) and proteins, among which are the lateembryogenesis abundant proteins (LEA) (Blackman et al., 1995; Dure, 1993; Close, 1996; Ingram and Bartels, 1996). LEA proteins were found in the seeds of several plants and in vegetative organs, especially under abiotic stress conditions (Thomashow, 1999; Hundertmark and Hincha, 2008). According to amino acid sequence homology, LEA proteins have been separated into different groups (Hundertmark and Hincha, 2008). From these groups the LEA D11 family (LEA type 2 proteins), also known as Dehydrins (Close, 1997), have been estimated to comprise up to 4% of the total seed protein. (Wise and Tunnacliffe, 2004). Expression of the Dehydrin proteins have been found to be associated with the protection of various types of plant cells from osmotic stresses, such as those caused by desiccation, salt, and low temperatures (Skriver and Mundy, 1990; Close, 1996; Ingram and Bartels, 1996; Allagulova et al., 2006). Hyper-osmotic conditions and low temperatures cause cellular dehydration, resulting in the reduction of cytosolic volumes and the alteration of cellular mechanisms. Toward survival, plants accumulate Dehydrin proteins during these conditions in the dehydrating plant tissue, (Abba et al., 2006). Several studies revealed that Dehydrins are widely distributed in the plant kingdom (Abba et al., 2006), in brown algae (Li et al., 1998), in lichen Selaginella lepidophylla (Close, 1997) and in cyanobacterium (Close et al., 1993). A number of Dehydrin proteins have been isolated and studied; the physiochemical and/or structural mecha