Enabling technologies for manipulating multiple genes on complex pathways

Many complex biochemical pathways in plants have now been manipulated genet ically, usually by suppression or over-expression of single genes. Further exploitation of the potential for plant genetic manipulation, both as a res earch tool and as a vehicle for plant biotechnology, will require the co-or dinate manipulation of multiple genes on a pathway. This goal is currently very difficult to achieve. A number of approaches have been taken to combin e or 'pyramid' transgenes in one plant and have met with varying degrees of success. These approaches include sexual crossing, re-transformation, co-t ransformation and the use of linked transgenes. Novel, alternative 'enablin g' technologies are also being developed that aim to use single transgenes to manipulate the expression of multiple genes. A chimeric transgene with l inked partial gene sequences placed under the control of a single promoter can be used to co-ordinately suppress numerous plant endogenous genes. Cons tructs modelled on viral polyproteins can be used to simultaneously introdu ce multiple protein-coding genes into plant cells. In the course of our wor k on the lignin biosynthetic pathway, we have tested both conventional and novel methods for achieving co-ordinate suppression or over-expression of u p to three plant lignin genes. In this article we review the literature con cerning the manipulation of multiple genes in plants. We also report on our own experiences and results using different methods to perform directed ma nipulation of lignin biosynthesis in tobacco.