High throughput approaches for the identification of salt tolerance genes in plants

Salt tolerance in plants is a complex trait, which involves multiple genes participating in a myriad of processes that limit uptake, promote efflux, enhance vacuolar storage of Na⁺ and recycle Na⁺ from shoots to roots. In addition, the suppression of high Na⁺-triggered oxidative stress and cell death also increases salt tolerance. A number of salt tolerance genes have been identified and characterized using arabidopsis and rice as model plants. Mutant screens have been frequently utilized and most genes identified with this approach are overly-sensitive to salt stress, i.e.sos genes, implying that positive gene function is required for salt tolerance. To identify genes that positively contribute to salt tolerance and are more easily transferred to crops, Ceres has developed a large population of arabidopsis transgenic lines overexpressing genes from several species and used a seed pooling strategy to screen these for enhanced salt tolerance. Thus far, we have identified 10 genes that when overexpressed result in increased salt tolerance. The encoded proteins are related to calmodulin, calmodulin-binding, zinc-finger, putative cyclases, stress-related and novel proteins. These genes may be involved in the regulation of AtNHX1 and/or SOS genes, as well as the suppression of high Na⁺-triggered generation of reactive oxygen species and cell death. We discuss methods, such as stacking genes that provide different mechanisms for salt tolerance or using salt inducible promoters, to develop super-tolerant cultivars of crops to be grown in high salinity soils