Previous Methods
Classical breeding programs develop new traits by combining different germ plasms in order to exploit natural or artificially induced diversity and, subsequently, to select for desired properties.
Classical genetic methods based on crosses and selection schemes have made enormous contributions towards stress-related crop improvement, tolerance to stress is generally considered a quantitative trait, and it is difficult to isolate specific genes involved in stress tolerance.
Historically, research on the effects of stresses has been largely descriptive by necessity, and relevant genes have been identified either by reference to physiological evidence or by differential screening. A large number of genes with potential roles in stress tolerance have been described and, in consequence, studies examining the control mechanisms of gene expression and analysing putative regulatory pathways have been initiated.
The problem with traditional plant breeding is that it is time consuming and laborious; it is difficult to modify single traits; and it relies on existing genetic variability. However, genetic engineering can now be used as a relatively fast and precise means of achieving improved stress tolerance. Many organisms have evolved traits that enable them to survive in extreme environments, and thus the gene(s) that confer these properties can potentially be introduced into higher plants.
Most of the earliest GM plants on the market were one step solutions. It only takes one protein to neutralise a herbicide or deter a pest. Stresses like drought however, can trigger one to two thousand plant genes. The ´Late Embryogenesis Abundant´ or ´LEA´ family of proteins, which responds to water-deficit, high salinity, or freezing stress, is just one example. There are probably 50 or so different LEA proteins. These can be classified into a series of groups. Within each group, you´ll have a series of family members, anywhere from one to ten or so. Up to 4% of the total protein content of an embryo can be comprised of just one of these LEA proteins.