Molecular strategies for developing salt tolerant crops

Salinity is one of the most important abiotic stresses for agricultural crops. High concentrations of salts cause hyperosmotic and ionic stresses, which, in turn, may generate secondary stresses such as oxidative stress, etc. The complexity and polygenic nature of salt tolerance trait has seriously limited the efforts to develop salt-tolerant crop varieties. This paper reviews new molecular strategies that have been or can be used for the molecular dissection of plant responses to salt stress, discovery of novel structural and regulatory genes involved in stress adaptation, and transgenic and molecular marker strategies used for engineering salt tolerance in plants. Application of novel techniques such as genome sequencing, high-throughput analysis of genomic-scale expressed sequence tags (ESTs), DNA chips/cDNA microarray analyses, targeted or random mutagenesis, knockouts, molecular mapping and gain-of-function or mutant complementation, is expected to accelerate the discovery of the new genes involved in stress adaptation as well as improve understanding of stress biology. A number of stress-related genes have been characterized including the ones that encode for important enzymes or a biochemical pathway, participate in signaling pathways or act as transcriptional regulators for coordinated regulation of stress related genes. Some of these genes have been successfully transferred in model plant species including Arabidopsis, rice and tobacco, and a marginal to significant improvement in salt-tolerance has been reported. In addition, molecular markers can be used for linkage mapping of genes/QTLs for salinity tolerance trait, marker-assisted transfer and pyramiding of such QTLs into agronomically desirable genotypes and/or for map-based cloning of genes. Application of transgenic and molecular marker research coupled with rapid gene discovery via functional genomic research in plants shall provide effective means for designing salt-tolerant crops