Nitrogen and carbon metabolism in plastids: evolution, integration, and coordination with reactions in the cytosol

Plastids are diverse organelles that differ in form and function depending on their location within a plant. Their evolutionary origin, as free-living cyanobacteria, has left remnants of autonomy, and whereas the majority of the genetic control now lies within the nucleus, in terms of metabolism the plastid is fundamental to the life of the cell. This chapter describes the involvement of the plastid in carbon and nitrogen metabolism, in particular nitrate and ammonium assimilation, the Calvin cycle, oxidative pentose-phosphate pathway, glycolysis, and terpenoid biosynthesis. We have selected these pathways because they provide an opportunity to describe the metabolic interchange between plastids and cytosol and show duplication of some or all of the reactions in these two subcellular compartments. We discuss current knowledge of the likely ancestry of the genes encoding these pathways and consider how this has contributed to the compartmentation of nitrogen and carbon metabolism within the cell.