Under natural conditions, opine promoters drive the expression of opines (i.e. mannopine, octopine, nopaline), hormone-like compounds generated by the soil bacterium Agrobacterium through the use of the plant’s expression machinery. Opines are utilized by the bacterium as a source of carbon, nitrogen and energy. Promoters from the nopaline synthase (nos), octopine synthase (ocs) and mannopine synthase (mas) genes have been isolated and inserted into transformation vectors upstream of foreign genes to control the expression of those genes.
Although these promoters are regarded as constitutive, their level of activity can be affected by hormones and wounding. Nevertheless, they are still frequently used, mainly for transformation of dicotyledonous (dicot) plants. Additionally, depending on the orientation, some functional parts of regulatory sequences associated with promoters, such as the maspromoters, have the ability to bind nuclear protein factors from different plants and can be used as enhancers or silencers.
Granted patents related to transcriptional regulatory elements derived from opine synthase genes may be divided into three groups:
- Promoters and UAS from opine synthase genes: Patents granted in the U.S. and Australia directed to promoters and upstream activating sequences (UAS) derived from opine synthase genes, especially from the ocs and mas genes of A. tumefaciens;
- 35S-enhanced mas promoter: Patents granted in the U.S. and Canada directed to a mas promoter enhanced by a UAS from CaMV 35S gene; and
- Enhancers from the ocs gene: Patents granted in the U.S., Europe and Canada directed to enhancer sequences isolated from the ocs gene of particular use in the transformation of monocots.