Box 2.7: New Approaches to Plant Stress Tolerance

Past efforts to improve plant tolerance to drought, high salinity and temperature stress through conventional plant breeding and/or genetic engineering have had limited success, largely due to the complexity of stress responses. More rapid progress is now expected through comparative genomic studies of a diverse set of model organisms, and through the use of new techniques. The latter include techniques such as high-throughput analysis of expressed sequence tags (ESTs), large scale parallel analysis of gene expression, targeted or random mutagenesis and gain-of-function or mutant complementation. The discovery of novel genes, determination of their expression patterns in response to abiotic stress, and an improved understanding of their roles in stress adaptation (through functional genomic studies and proteomics), will provide the basis of new strategies to improve stress tolerance in crops.

Genetic engineering of abiotic stress tolerance traits

Genetic engineering offers the possibility of the direct introduction into a target plant of a small number of genes. In regard to improving tolerance to abiotic stresses, experimental strategies rely on the transfer of one or more genes that encode either biochemical pathways or endpoints of signaling pathways that are controlled by a constitutively active promoter. These gene products protect the plant, either directly or indirectly, against environmental stresses. A lack of understanding of metabolic flux, and the interrelationship of osmotic, desiccation and temperature tolerance mechanisms, and their corresponding signaling pathways have limited the success of these transgennic approaches in plants. It is anticipated that new developments in genomics and proteomics will offer more information and new strategies for managing abiotic stress in plants.

Genomic analysis for abiotic stress tolerance

Studies (using EST and genomic sequencing and cDNA microarray analysis) are seeking to identify the complement of genes essential for tolerance to osmotic potential, desiccation, or temperature stress, respectively. The large data sets being assembled will be integrated and compared with plant species naturally tolerant to these stresses in order to identify tolerance mechanisms that are conserved across species.

Approaches with proteomics will also be necessary to assess the protein modifications that are relevant to stress tolerant phenotypes. The functional determination of all genes that participate in stress adaptation or tolerance is expected to provide an understanding of the biochemical and physiological basis of stress responses in plants. With this information derived from model plants such as Arabidopsis, it should become possible to manipulate and optimise stress tolerance traits for improved crop productivity.

Source: Cushman and Bohnert 2000

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