High-level and ubiquitous expression of the rice cytochrome c gene OsCc1 and its promoter activity in transgenic plants provides a useful promoter for transgenesis of monocots.

Expression patterns of a rice (Oryza sativa) cytochrome c gene OsCc1 and its promoter activity were characterized in transgenic rice plants. OsCc1 transcripts accumulate in most cell types, but to varying levels. Large amounts of OsCc1 transcripts are found in the roots, calli, and suspension cells, but relatively lower in mature leaves, demonstrating its higher levels of expression in non-photosynthetic tissues. Unlike the human cytochrome c gene, which is responsive to cAMP, OsCc1 expression is not enhanced in various rice tissues after dibutyryl cAMP treatments. OsCc1 promoter was linked to the sgfp gene and its activities in different tissues and cell types of transgenic rice plants were analyzed in comparison with the Act1 and RbcS promoters. OsCc1 promoter directs expression in virtually all organs of transgenic plants including roots, leaves, calli, embryos, and suspension cells, showing a particularly high activity in calli and roots. Activity of the OsCc1 promoter was 3-fold higher than Act1 in calli and roots and comparable with RbcS in leaves, representing a useful alternative to the maize (Zea mays) Ubi1 and the rice Act1 promoters for transgene expression in monocots.