Evolving strategies for the genetic engineering of herbicide resistance in plants

Developments in plant genetic engineering technology will shortly permit the commercial introduction of transgenic crop varieties resistant to a number of non-selective herbicides. High levels of tolerance have been achieved both by overexpression of a target protein and by modification of that target to an insensitive form. However the results of preliminary trials suggest that in some instances the yield penalty for such genetic alterations will be prohibitive. An alternative strategy, based on the transfer and expression of a gene encoding a herbicide-detoxifying enzyme, appears to offer high resistance levels at low metabolic cost and is expected to assume increasing importance, although it may not prove suitable for all herbicides.