Evaluation of tissue specificity and expression strength of rice seed component gene promoters in transgenic rice

Using stable transgenic rice plants, the promoters of 15 genes expressed in rice seed were analysed for their spatial and temporal expression pattern and their potential to promote the expression of recombinant proteins in seeds. The 15 genes included 10 seed storage protein genes and five genes for enzymes involved in carbohydrate and nitrogen metabolism. The promoters for the glutelins and the 13 kDa and 16 kDa prolamins directed endosperm-specific expression, especially in the outer portion (peripheral region) of the endosperm, whilst the embryo globulin and 18 kDa oleosin promoters directed expression in the embryo and aleurone layer. Fusion of the GUS gene to the 26 kDa globulin promoter resulted in expression in the inner starchy endosperm tissue. It should be noted that the 10 kDa prolamin gene was the only one tested that required both the 5' and 3' flanking regions for intrinsic endosperm-specific expression. The promoters from the pyruvate orthophosphate dikinase (PPDK) and ADP-glucose pyrophosphorylase (AGPase) small subunit genes were active not only in the seed, but also in the phloem of vegetative tissues. Within the seed, the expression from these two promoters differed in that the PPDK gene was only expressed in the endosperm, whereas the AGPase small subunit gene was expressed throughout the seed. The GUS reporter gene fused to the alanine aminotransferase (AlaAT) promoter was expressed in the inner portion of the starchy endosperm, whilst the starch branching enzyme (SBE1) and the glutamate synthase (GOGAT) genes were mainly expressed in the scutellum (between the endosperm and embryo). When promoter activities were examined during seed maturation, the glutelin GluB-4, 26 kDa globulin and 10 kDa and 16 kDa prolamin promoters exhibited much higher activities than the others. The seed promoters analysed here exhibited a wide variety of activities and expression patterns, thus providing many choices suitable for various applications in plant biotechnology.