Altering the level of expression of key transcription factors inv

Altering the level of expression of key transcription factors involved in abiotic stress pathways has been shown to enhance tolerance to var ious abiotic stresses may in Arabidopsis as well as in important crop species such as rice, maize, and alfalfa. Traits involving tolerance to abiotic stresses are con sidered to be more complex than those that are cur rently commercialized due to the large number of genes and pathways that may be affected. Furthermore, the interaction between plants and the environment is an intricate, continuous process that has been difficult to characterize, further adding to the complexity of manip ulating abiotic stress tolerance traits. The increased complexity of these traits may correspond with a greater potential for unintended effects Inhibitors,Modulators,Libraries to occur in transgenic plants.

In transgenic systems, two different types of unin tended effects are generally known to occur. Posi tion effects are attributed to the insertion of a transgene at a particular locus in the genome and the resulting interference this might cause. These effects will vary with the site of integration and will therefore be unique to Inhibitors,Modulators,Libraries each independent plant line. Position effects can be easily eliminated by screening for plant lines that have no or little position effects. In contrast, pleiotropic effects are independent of the site of transgene insertion and are the sum of all the phenotypic effects caused by expression of the transgene. While some of these may be the intended trait, others may occur through unex pected interactions of the gene with plant processes and constitute the unintended pleiotropic effects.

These effects are of greater interest since Inhibitors,Modulators,Libraries they are more diffi cult to eliminate and more likely to create safety issues. Engineering more complex traits such as abiotic stress tolerance in plants through Inhibitors,Modulators,Libraries the manipulation of tran scription factors may uncover cryptic properties of the transcription factor that could produce some of the unintended pleiotropic effects. Many transcription fac tors are part of large families that have complex evolu tionary histories. These families typically arise through gene duplications followed by Inhibitors,Modulators,Libraries functional diver gence in separate expression domains or through the acquisition of new functions. These processes often result in functional redundancies within the families that can be difficult to detect. Furthermore, some tran scription factors may retain ancestral functions that are sometimes only revealed Tipifarnib by altering the normal pattern of expression. Therefore the manipulation of transcrip tion factors in engineering complex traits such as abiotic stress tolerance may be likely to produce unintended pleiotropic effects.

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