Rice Genetics IV - IRRI books - International Rice Research Institute

ously. Indeed, earlier attempts to increase PEPC activity in transgenic C 3 plants reportedonly a 0.5- to 3-fold increase in activity.Similarly, transgenic rice carrying the PPDK gene from maize also showed 40-fold higher enzymatic activity than that of nontransformed rice. In some transformants,the level of the PPDK protein was extraordinarily high, and it amounted to 35% oftotal leaf-soluble protein. It was comparable with that of the large subunit of Rubisco,the most abundant protein in leaves of C 3 plants (Fig. 4). Such high-level expressionis not solely caused by the transcriptional activity of the maize PPDK gene, sinceexpression of the corresponding cDNA under the control of either the promoter of themaize C 4 -specific PPDK gene or the rice Cab promoter increased the activity lessthan 5-fold. Therefore, it is possible that the presence of exons and introns and/or theterminator sequence in intact genes acts to confer the high-level expression. N-terminalamino acid sequencing indicated that the maize PPDK protein expressed in riceleaves was located exclusively inside the chloroplast. Analysis of transgenic rice plantsshowed that C 3 plants can be produced with high levels of C 4 -specific enzymes.Transgenic riceMaizeRicePD272PD332PD259PD317PD278PEPCPPDKPPDKRubisco LSUFig. 4. Polypeptide profiles of leaf-soluble protein in maize, rice, andhomozygous lines of transgenic rice carrying the intact maize Pdk gene.Protein was stained with Coomassie brilliant blue R-250. LSU = largesubunit of Rubisco. (From Matsuoka et al 2000.)High-level expression of C 4photosynthetic genes in transgenic rice 443