Functional analysis of the promoter of a rice 18 kDa oleosin gene

The 18 kDa oleosin (Ole18) is a seed-specific protein expressed specifically in embryos and the aleurone layers of rice (Oryza sativa L.) seeds. Sequence analysis revealed that the promoter of the gene Ole18 contains many cis-acting elements, including seed-specific elements, ABA-responsive elements, and drought-responsive elements, mainly in the region between -400 and -100. To elucidate the regulatory mechanism of Ole18 gene expression, the 1249-bp Ole18 promoter and its internal deletion-derivatives were fused to the GUS reporter gene and introduced into rice. Histochemical analysis and fluorometric quantitative analysis in transgenic rice showed that GUS activity varied depending on the deletion-derivative construct. GUS activity decreased as the deletion region increased (from -378 to -187, to -180, to -169, and to -130), suggesting the importance of known cis-acting motifs such as ABA-responsive elements and drought-responsive elements, and a novel motif within these regions. In addition, either the region between -378 and -179 or that between -179 and -130 was sufficient to induce high expression in the embryos and aleurone layers. This suggests the importance of the common cis-acting elements in the two regions: the drought-responsive element DRE2 and the ABA-responsive element ABI4-binding motifs.