Recombinant DNA technology is being implemented as a way of improving plant breeds. Using this technology, plants with additional functions such as herbicide resistance, pest insect resistance, and the like have been created, and progress is being made in their practical application. The use of recombinant technologies to improve plant breeds not only aims to add new functions to plants: there has been much research and development into the expression of useful proteins in plants, by introducing these plants with a foreign gene. Such research uses plants as factories to produce useful proteins.
Production of recombinant proteins in plants has many advantages, the most evident of which are the reduced cost compared to systems that utilize transgenic animals; the ease with which scale of production can be adjusted to suit market size; and the absence of any risk of contamination by animal-borne pathogens such as viruses and prions (Daniell et al., Trends Plant Sci., 6, 219–226 (2001); Fischer and Emans, Transgenic Research, 9, 279–299 (2000); Giddings et al., Nature Biotech., 18, 1151–1156 (2000)).
Recently, systems using seeds for production of recombinant protein in plants have been shown to be more advantageous than those using leaves or roots (Delaney, 2002, Plants as Factories for Protein Production (Hood, E. E. and Howard, J. A) pp. 139–158 (2002). Netherlands: Kluwer Academic; Howard and Hood, Plants as Factories for Protein Production (Hood, E. E. and Howard, J. A) pp. vii–x (2002). Netherlands: Kluwer Academic). Seeds are storage organs, in which a special organelle called a protein body stably stores a large amount of a small number of storage proteins. This feature has been employed by using seeds as ideal bioreactors for producing recombinant protein. Recombinant proteins accumulated in seeds are very stable, and can be administered orally without any need for further processing or purification. Antibodies or vaccines expressed in seeds are reported to be highly stable, and can be stored for years, even at room temperature, without decomposition. Moreover, vaccines administered via seeds are thought to trigger antibody production by the mucosal immune system, without processing or purification (Walmsley and Arntzen, Curr. Opin. Biotech., 11, 126–129 (2000)).
When producing proteins using recombinant technology, the yield of a protein of interest is affected by many factors, including transcription factors. The most important and easily controlled of these factors is the choice of promoter. In order to use rice seeds as a platform for recombinant protein production, it is important to use a promoter suited to the needs of individual proteins and their use in biotechnology. This is because the promoter controls the timing, location and level of expression.
However, analyses of the cis-regulatory factors involved in endosperm-specific expression are limited to those of a small number of glutelin genes, using different species (transgenic tobacco) and the same species (transgenic rice). (Croissant-Sych and Okita, Plant Sci., 116, 27–35 (1996); Takaiwa et al., Plant Mol. Biol., 16, 49–58 (1991a); Takaiwa et al., Plant Mol. Biol., 30, 1207–1221 (1996); Wu et al., Plant J., 14, 673–983 (1998a); Wu et al., Plant J., 23, 415–421 (2000); Yoshihara et al., FEBS Lett., 383, 213–218 (1996); Zhao et al., Plant Mol. Biol., 25, 429–436 (1994); Zheng et al., Plant J., 4, 357–366 (1993)). Studies of a few other rice storage protein promoters were no more than observations of their spatial expression patterns (Wu et al., Plant Cell Physiol., 39, 885–889 (1998b)).