Poster: Photosynthesis (carbon)

Abs # 228: An upregulated pyruvate orthophosphate dikinase isoform in C₄ Hydrilla leaves

Presenter:	Rao, Srinath K., skrao@ufl.edu
Authors	Rao, Srinath K. (A)   Davison, Nicole A. (A)   Estavillo, Gonzalo M. (A)   Reiskind, Julia B. (A)   Bowes, George  (A)
Affiliations:	(A): Department of Botany, University of Florida

Hydrilla verticillata is an aquatic monocot with a well-documented facultative C₄ photosynthetic system that serves as a model for generating a transgenic C₄ rice plant. Although Kranz anatomy is absent, fixation events are separated intracellularly between cytosol and chloroplast; thus, both Calvin and C₄ cycles operate in the same cell. Molecular studies in our laboratory have identified multiple isoforms of phosphoenolpyruvate carboxylase (PEPC) and the decarboxylase NADP-malic enzyme (Bowes et al 2002). At least one isoform from each is implicated in the C₄ system of Hydrilla. We are investigating another key enzyme of the C₄ pathway, pyruvate orthophosphate dikinase (PPDK), which regenerates the substrate, phosphoenolpyruvate, for the PEPC reaction. Both the activity and protein levels of PPDK are upregulated when the C₄ system is induced (Magnin et al 1997). Using differential display techniques we have identified a partial cDNA sequence that was overexpressed in Hydrilla C₄ leaf material and encoded a putative chloroplastic isoform of PPDK. A database search revealed a close match with the PPDK from Mesembryanthemum crystallinum and Zea mays. Subsequent studies using macroarray technology and Northern analyses corroborated the expression data obtained from the differential displays. Characterization of this and other isoforms encoding PPDK is curently underway. Supported by USDA NRICGP 2002-35318-12540.