Identification and Isolation of Differentially Expressed Gene in Response to Cold Stress in a Green Alga, Spirogyra varians (Zygnematales)

Abstract

In plants, cold adaptation is characterized by various morphological and physiological transitions. Plant survives cold stress using various methods. Some plants produce antifreeze protein (Guy et al. 1985) or change the composition of lipid and carbohydrate in the cell (Guy 1990) to increase the ability to endure cold stress; but most plants regulate expression of certain gene group to adjust to cold stress (Thomashow 1990). There are many reports on the cold stress regulated genes of higher plants as wheat, barley and Arabidopsis spp. (Graham and Patierson 1982; Cattivelli and Bartels 1990; Hajela et al. 1990; Gilmour et al. 1992; Danyluk et al. 1994; Houde et al. 1995; Pearce et al. 1998), but little is known about the cold stress genes and cold acclimation mechanism in algae. Cold shock can damage a freshwater alga much more seriously than higher plants because most of over-wintering freshwater algal cells are directly exposed to freezing waters during winter time. In order to maintain their functions under cold stress, freshwater alga must have been developing some unique cold acclimation mechanisms. Spirogyra varians grows in shallow ponds in Korea from late January to April. The water repeats freezing and thawing during this period. This species is often found growing under the ice. When blue light is given, plants move toward to the light source and this phototrophic movement is affected by temperature (Kim et al. 2005). Differential displayed (DD)-PCR has been developed to identify and isolate differentially expressed genes (Liang and Pardee 1992) and is extensively applied to various ranges of gene expression analyses because of its effectiveness and convenience. One of the advantages of this technique is that it requires only small amount of RNA since this technique is PCR-based. However, relatively high chance to have false-positive acts is a major handicap in this technique. Many efforts have been attempted to improve the specificity of DD-PCR (Liang et al. 1993, 1994). Recently modification to eliminate falsepositive acts has been developed by increasing the annealing specificity with specially designed annealing control primers (ACP) system (Hwang et al. 2003; Kim et al. 2004). In this study, we analyzed the cold stress associated genes in Spirogyra varians by differential expression gene (DEG) technique using ACP system. A coldAlgae Volume 22(2): 131-139, 2007