Gene expression profiling of plants under salt stress

Soil salinity is among the leading environmental stresses affectingglobal agriculture, causing billions of dollars in crop damagesevery year. Regardless of the cause, ion toxicity, water deficit, ornutritional imbalance, high salinity in the root zone severely im-pedes normal plant growth and development, resulting in reducedcrop productivity or crop failure. Development of salt-tolerant cultivarsis an attractive and economical approach to solving thisproblem. Although several salt-tolerant plant genotypes have beendeveloped through transgenic approaches, often they have failedor exhibited limited success under field saline conditions. This isdue to several reasons, including the fact that plant growth anddevelopment under saline conditions in the field is often influencedby cumulative effects of multiple environmental stresses andgenetic factors, which may not have been considered during thedevelopment of salt-tolerant transgenic plants. Adoption of inappropriatescreening techniques or selection criteria may also leadto selection of genotypes that may not be stress tolerant in a realsense. In most plant species, salt tolerance is a genetically complextrait, often modulated by multiple biosynthetic and signalingpathways. Cross-talks among various stress-controlling pathwayshave been observed under salt stress, many of which are regulatedby transcription factors. Thus, a comprehensive knowledge of theup- and downregulating genes under salt-stress is necessary, whichwould provide a better understanding of the interactions amongpathways in response to salt stress. Attaining such knowledge is agood step toward successful development of salt-tolerant crop cultivars.To this end, DNAmicroarray technology has been employedto study expression profiles in different plant species and at varyingdevelopmental stages in response to salt stress. As a result, largescalegene expression profiles under salt stress are now availablefor many plant species, including Arabidopsis, rice, barley, andice plant. Examinations of such gene expression profiles will helpunderstand the complex regulatory pathways affecting plant salttolerance and potentially functional characterization of unknowngenes, which may be good candidates for developing plants withfield salt tolerance. In this article, we review and discuss the currentknowledge of plant salt tolerance and the extent to which expressionprofiling has helped, or will help, a better understanding ofthe genetic basis of plant salt tolerance. We also discuss possibleapproaches to improving plant salt tolerance using various tools ofbiotechnology.