DIFFERENTIAL GENE EXPRESSION IN RESPONSE TO SALT STRESS IN Vicia monantha

Abstract

Vicia monantha is a member of the family Fabaceae, belonging to the genus Vicia. It is a wild plant species that is native to the Northern African region, particularly Algeria and Egypt. It is char- acterized by its noticeable withstanding of severe environmental conditions. Such wild plants are considered as an excellent source of stress-related genes awaiting their isolation and identification.
Some species of Vicia, such as V. faba (broad bean), V. narbonensis (narbon vetch), V. villosa (hairy vetch) and V. sativa (common vetch), represent eco- nomically important crops that are widely cultivated as a green manure cover, as well as grain and straw crops for animals and a soil binder throughout the North Temperate Zone of the new and old worlds.
Wild Vicia species, such as V. cordata, V. nigra, V. narbonensis, V. sativa, V. monantha and V. villosa, are of great interest to agronomists and plant breeders as crop plants in their own right and as possible sources of germplasm for cultivated Vicia faba (Atlas of legume plant of the North West of Egypt, 1993).
Plants are frequently exposed to stresses, which are usually defined as external factors exerting disadvantageous influences on them (Levitt, 1972). Water deficit, chilling and freezing, heat stress, salinity and oxygen deficiency are major stress factors restricting plant growth (Boyer, 1982; Salisbury and Ross, 1989). Some of which (such as temperature) can become stressful in a few minutes; others may take days to weeks (soil water) or even months (mineral nutrients) to become stressful. Salinity can affect any process in the plant life cycle, so that tolerance will involve a complex interplay of characters. Many researchers investi- gated details of the physiology and biochemistry of salt tolerance and also looked at methods to screen overall plant performance that could be used in breeding programs. In general, plants are relatively tolerant during germination but become more sensitive during emergence and early seedling up to later stages of growth (Azhar and McNeilly, 1989; Abdel-Tawab et al., 1998). Drought and salinity are becoming particularly wide- spread in many regions, and are expected to cause serious salinization of more than 50% of all arable lands by the year 2050. Drought, salinity, extreme temperatures and oxidative stress are often intercon- nected, and may induce similar cellular damage. For example, drought and/or salinization are manifested primarily as osmotic stress, resulting in the disruption of homeostasis and ion distribution in the cell (Serrano et al. 1999; Zhu, 2001).
Cloning and characterization of environmental stress-induced genes have greatly contributed to our understanding of the physiological responses of plant cells at the molecular level to different environmental factors. cDNA-amplified fragment length polymorphism (cDNA- AFLP) is an efficient, sensitive, and re- producible technology for the isolation of differentially expressed genes (Bachem et al., 1996). It requires no prior sequence information and is, therefore, a useful tool for the identification of novel genes (Ditt et al., 2001). cDNA-AFLP is widely avail- able at a low cost for various plant spe- cies, even if there is little information at the molecular level (Breyne and Zabeau, 2001; Bei et al., 2006; El-Khishin, 2003; Ge et al., 2007; Niranjan et al., 2006; Roshandel, 2007). It is a polymerase chain reaction (PCR)-based technology like differential display (DD), but featuring higher reproducibility and availability. The most critical advantage is that cDNA- AFLP is based on linker-ligated PCR, whereas DD is based on arbitrarily primed PCR (Bachem et al., 1996; Pardee and McClelland, 1999; Shokry et al., 2007).
The objective of this study was to isolate and characterize some of the key expressed sequence tags (ESTs) in re- sponse to salt stress in Vicia monantha using cDNA-AFLP technique, clone and sequence the isolated ESTs and determine gene functions for each EST.