Expression analyses of a rice 10 kDa sulfur-rich prolamin gene

Expression analyses of genes encoding sulfur-rich 10 kDa rice prolamins have not been reported to date although the entire genome of the model monocot plant has been sequenced in recent years. We isolated a 10 kDa rice prolamin gene, RP10, by genomic PCR, and the gene was registered in GenBank under the accession number AF294580. Genomic Southern-blot and bioinformatic study revealed that genes encoding RP10 homologes (class IV rice prolamins) were composed of two to three copies per haploid genome in Japonica cultivars Tainung 67 and Nipponbare. To elucidate the temporal and spatial expression of RP10, we introduced a chimeric gene that consisted of the 836 bp upstream sequence of RP10 and the coding regions of β-D-glucuronidase (GUS) into rice via Agrobacterium tumefaciens mediated transformation. The expression levels of GUS followed the accumulation pattern of endogenous RP10 transcript in parallel, indicating that the expression of GUS did reflect the endogenous temporal control of RP10 gene. Maximal GUS activity was reached at 12~20 days after flowering (DAF) in maturing seeds. Histochemical analysis showed that the specific expression of GUS in seeds was not restricted to the endosperm cells, but also occurred in the vascular bundle and epithelial cells of scutellum. In comparison with promoters of other rice storage protein genes, RP10 promoter exhibited a high expression level, with a long plateau period. Our studies suggest that RP10 promoter could be potentially useful for over-expression of foreign genes in transgenic rice seeds.