Project description:Bienertia sinuspersici performs C4 photosynthesis without Kranz anatomy through subcellular compartmentalization of carbon fixation within individual cells. In this species, central compartment chloroplasts (C) and peripheral chloroplasts (P) collaborate with cytosolic and mitochondrial components in a NAD-ME type C4 cycle. How the two functionally different chloroplast types can develop within individual cells and the mechanism of import of nuclear encoded, plastid targeted proteins are currently unknown. We used 454 sequencing in combination with large scale label-free proteomics to determine the distribution of photosynthesis-related proteins. Subcellular localization of 169 protein was determined through comparison of protein abundance in four different subcellular fractions. 39 out of the 120 chloroplastic proteins showed differential accumulation between the two chloroplast types. Rubisco, RPP regenerative phase and PSII related proteins accumulated in C chloroplasts whereas C4 related proteins and the NDH complex were more abundant in P chloroplasts. Comparison of transit peptides of differential accumulating proteins indicated no obvious sequence homology or similarities in physico-chemical properties between members of the same group. Protein composition analysis of the central compartment indicated that mitochondria and peroxisomes are the only major components besides chloroplasts in this compartment. The combined information from subcellular and developmental protein profiling was used to generate a first draft of the protein machinery involved in single-cell C4 photosynthesis.
