[P4] Crop Genetics and Physiology

[P4-07] Engineering CAM Traits into C3 crops

^○Aoi Saito¹, Mie Wakabayashi², Shiori Terai², Shiori Yamabe², Satoko Kobayashi², Kazuyuki Saito³, John C. Cushman⁴, Sakae Agarie³ (1.Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Japan, 2.Faculty of Agriculture, Kagawa University, Japan, 3.Faculty of Agriculture, Kyushu University, Japan, 4.Department of Biochemistry and Molecular Biology, University of Nevada, United States)

Crassulacean acid metabolism (CAM) is a carbon fixation pathway that evolved as an adaptation to limited water availability. CAM species exhibit extremely high water-use efficiency. CO₂ is fixed during the night by phosphoenolpyruvate carboxylase (PEPC) and produced malic acid is accumulated in the vacuole. PEPC is activated by phosphorylation, which is catalyzed by PEPC kinase (PPCK). During the day, the malic acid is decarboxylated to release CO₂ by NADP-malic enzyme (NADP-ME). The PEPC, PPCK, and NADP-ME were encoded by McPpc1, McPPCK and Mod1, respectively. We isolated intron-containing genes (with and without promoter region), cDNA and antisense cDNA of those genes from Mesembryanthemum crystallinum. We constructed vectors including the cDNA of McPpc1 and McPPCK, which were fused to a promoter of circadian clock associated1 (CCA1), which regulates gene expression at night, and Mod1, which was fused to the promoter of Chlorophyll a-b binding protein (Cab), which regulated gene expression at day. These promoters were isolated from Arabidopsis thaliana. We obtained transgenic Arabidopsis that expressed McPpc1 and McPpck during the night at a higher level. The expression levels of these genes were about 6 and 3 times higher than those in M. crystallinum, respectively. The PEPC activity of McPpck transgenic Arabidopsis was about 2 times higher than that of non-transformants. We applied the same strategy to rice to confer CAM traits.