PARENT SESSION
Posters P8C C4 and CAM. Abstracts (685-698)

The role of pyruvate orthophosphate dikinase (PPDK) in the C₃ plant Arabidopsis thaliana. Kate Parsley^*,1, Julian Hibberd¹, ¹ Department of Plant Sciences, Cambridge, United Kingdom

ABSTRACT-

One of the key enzymes used during C₄ photosynthesis is pyruvate orthophosphate dikinase (PPDK). PPDK regenerates the primary acceptor of CO₂ in C₄ plants, phosphoenolpyruvate (PEP), from pyruvate in the chloroplasts of mesophyll cells. In C₃ plants, however, the role of this enzyme is unclear. We are using Arabidopsis thaliana to investigate the role of PPDK in C₃ plants.

We show that in Arabidopsis, a single ppdk gene produces two transcripts, these are identical apart from the presence of a single additional exon at the beginning of the longer transcript. We have shown via a gfp fusion construct that this additional exon codes for a chloroplast targeting peptide. The shorter transcript is controlled by a promoter located within the first intron and we believe it codes for a cytosolic protein.

Expression analysis using semi-quantitative RT-PCR and RNA blots shows that the two ppdk genes are differentially expressed and suggests that the longer ppdk transcript is abundant in cauline leaves and flowers. The shorter ppdk transcript is of lower abundance but is expressed in a greater number of tissues.

The role of the PPDK protein is being investigated using a homozygous T-DNA insertion line. Preliminary analysis of the PPDK mutant reveals compromised early seedling growth that can be rescued by the addition of sucrose to tissue-culture media.

Determining the role of PPDK in C₃ plants may provide evidence as to why the protein has been recruited into C₄ photosynthesis.

KEY WORDS: PPDK, C4 photosynthesis, Arabidopsis