Poster: Late and Moved Abstracts

Abs # 973: A proteomics approach to identify transport proteins in maize plastid envelopes

Presenter:	Braeutigam, Andrea , braeuti6@msu.edu
Authors	Braeutigam, Andrea  (A) (B)  Weber, Andreas PM (A)
Affiliations:	(A): Michigan State University (B): Genetics Program

The transport properties of plastid envelopes of the C4 plant maize differ from those of C3 plants due to the fact that C4 plants evolved a carbon concentration mechanism which allows more efficient CO₂ fixation. This process is compartimentalized, thus requiring numerous intra- and intercellular transport processes. In maize, the primary carbon acceptor is PEP (phosphoenolpyruvate) which is generated from pyruvate in mesophyll plastids. PEP is exported to the cytosol, carboxylated and the resulting OAA (oxaloacetate) is returned to the plastid where it is reduced to malate. Malate is shuttled to bundle sheath plastids where it is decarboxylated and oxidized yielding CO₂, NADPH and pyruvate. Pyruvate must then cross two plastid envelopes to be regenerated in mesophyll plastids. Hence, a high flux of OAA and malate as well as pyruvate across the plastid envelope is required. Neither a pyruvate transporter not a oxaloacetate/malate shuttle have been characterized at the molecular level to date. We hypothesized that the transporters catalyzing these high fluxes across the plastid envelope must be abundant and used a proteomics approach to identify abundant proteins. Plastid envelopes were isolated from maize leaves and a fraction enriched for hydrophobic proteins was separated by 1D SDS-PAGE. We obtained four prominent bands that were present in maize but not in C3 plant preparations. These candidate proteins were subjected to LC MS/MS and identified using grain EST databases. Here we report the proteomics approach and the preliminary characterization of the A.thaliana homologue of one of these proteins.