Functional Characterization of Cytosolic Pyruvate Phosphate Dikinase Gene (MecyPPDK) and Promoter (MecyPPDKP) of Cassava in Response to Abiotic Stress in Transgenic Tobacco

Pyruvate phosphate dikinase (PPDK) is a key enzyme in the photosynthesis of C-4 plants; its expression significantly affects the accumulation of photosynthetic products in C-4 plants. Pyruvate phosphate dikinase presents two subtypes, namely, chloroplastic PPDK and cytosolic PPDK. Cytosolic PPDK is ubiquitous in C-3 and C-4 plants. This subtype is also highly expressed in metabolically active storage organs. Cytosolic PPDK in cassava (Manihot esculenta Crantz, MecyPPDK) is considerately expressed mainly in functional leaves. However, research on the function of PPDK in cassava has not yet been reported. In this study, we cloned the 5' flanking sequence of MecyPPDK fused to the uidA reporter gene and stably transfected tobacco (Nicotiana benthamiana Domin). Slight b-glucuronidase activity was observed in transformed tobacco. This activity was upregulated remarkably under low temperature, drought, waterlogging, and abscisic acid treatments. Results suggest that MecyPPDK facilitates the survival of cassava plants in response to abiotic stress. Our results will provide further understanding regarding the regulation of MecyPPDK expression and a novel stress-inducible promoter in transgenic tobacco.