Light-regulated and organ-specific expression of a wheat Cab gene in transgenic tobacco.

Many of our most important crop plants are monocotyledons, including wheat, corn, rice and barley. No routine transformation system for monocotyledons has been reported, such as the Ti-mediated gene transfer system for dicotyledons facilitated by Agrobacterium tumefaciens. Indirect evidence suggests that Ti-plasmid DNA is transferred into and expressed in A. tumefaciens-infected wound tissues of plants from Liliaceae and Amaryllidaceae, but these observations have not been extended to monocotyledons of greatest agricultural importance. Regeneration of monocotyledons is usually blocked at the callus-stage, further complicating the possibility of exploring the regulated expression of their genes, and thus preventing identification of the regulatory domains of monocotyledonous genes in a homologous nuclear background. To circumvent these difficulties, we investigated whether monocotyledonous genes can be expressed and correctly regulated in dicotyledons. We have introduced a wheat gene (whAB1.6) encoding the major chlorophyll a/b binding protein (Cab) of the light-harvesting complex into the genomes of tobacco (Nicotiana tabacum SR1) and petunia (Petunia hybrida) via a Ti-DNA-mediated gene transfer system which allows the transformed cells to regenerate into whole plants. Here we report for the first time the light-regulated and organ-specific expression of a monocotyledonous gene in transgenic dicotyledonous plants.