Transient Gene Expression in Intact and Organized Rice Tissues.

Regulated gene expression of chimeric genes has been studied extensively in electroporated protoplasts. The applicability of these assays is limited, however, because protoplasts are not always physiologically identical to the cells from which they are derived. We have developed a procedure to electroporate DNA into intact and organized leaf structures of rice. Optimization of the new gene delivery system mainly involved eliminating explant-released nucleases, prolonging the DNA/explant incubation time, and expanding the pulse time. Using a [beta]-glucuronidase gene under the control of constitutive promoters, we demonstrated that all cell types within a leaf base were susceptible to electroporation-mediated DNA uptake. Although the technique was initially developed for leaf bases of young etiolated rice seedlings, we proved that it was equally applicable both to other monocotyledons, including wheat, maize, and barley, and to other explants, such as etiolated and green sheath and lamina tissues from rice. Transient gene expression assays with electroporated leaf bases showed that the promoter from a pea light-harvesting chlorophyll a/b-binding protein gene displayed both light- and chloroplast-dependent expression in rice, and that the promoter from the Arabidopsis S-adenosylmethionine synthetase gene was, as in transgenic Arabidopsis and tobacco, preferentially expressed in cells surrounding the vascular bundles.