Gene expression in transgenic rice with corn pollen-specific promoter Zmg13

A promoter fragment of the corn pollen-specific gene Zmg13 was evaluated for its control of gene expression in transgenic rice. Mature pollens of rice variety 'IR54' were bombarded with pCPPGUS containing the reporter gusA controlled by a 5' fragment of the Zmg13 gene (starting from the -260 bp position), and they exhibited transient GUS activity. Protoplasts of the rice variety 'Radon' that were treated with pCPPGUS in the presence of polyethylene glycol (PEG) did not exhibit transient GUS activity. To determine the activity of promoter Zmg13 in transgenic rice, 'Radon' protoplasts were co-transformed with pCPPGUS and p35SBarB (containing the bar gene that confers resistance to phosphinothricin [PPT], the active ingredient in the herbicide Basta) using PEG-mediated transformation. Transgenic plants resistant to Basta and showing GUS activity in the pollen were obtained after selection with 8 mg/L PPT at a selection efficiency of 86.6% and a co-transformation efficiency of 72%. GUS expression in the mature pollen was found to be influenced by the number of integration events and the physiological age of the pollen. Low gene copy integration events were found to yield GUS activity in about 50% of the mature pollens - the expected results based on the hemizygous condition of the T,, plants. Somatic tissues did not express, GUS. The results indicated that the corn pollen promoter functions in rice and controls the expression of the gusA gene in the expected developmental and tissue/cell-specific manner. This is the first report of a monocot pollen-specific promoter isolated from one species, corn, and expressed in another monocot, rice, in a developmental and cell-specific manner.