Transfection experiments were performed with DNA constructs bearing the GUS reporter gene and various promoter elements to assess meiosis specificity of expression. Plasmid DNA, pBI221, including the CaM 35S promoter fused to the GUS gene, was expressed in protoplasts derived from lily calli and young anthers but not microsporocytes. In contrast, plasmid DNAs bearing the meiotic promoter mei2Pro (δ12) and mei2Pro (δ12-s) isolated from Schizosaccharomyces pombe, fused to the GUS gene, were expressed in protoplasts from lily microsporocytes but not from somatic cells. Furthermore, DNAs with a mutated mei2 promoter fused to the GUS gene showed reduced activity. Transfection of the plasmid DNA, pUC19-recA-mei2, bearing mei2Pro (δ12) in front of the E. coli recA gene, was associated with higher recombinogenic activities assayable in vitro. The induction of GUS in meiocytes by transfection of plasmid DNA was dependent on the presence of mei2, as shown by the reduction of activity when the promoter was mutated and the stage of meiosis. The developmentally regulated expression of a yeast promoter in plant cells demonstrated in this paper may be the first to be reported.
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