Regulation of Rubisco gene expression in C4 plants.

Ribulose-1,5-bisphosphate-carboxylase/oxygenase (Rubisco) incorporates inorganic carbon into an organic form, making this chloroplastic enzyme one of the most essential factors for all life on earth. Despite its central role in photosynthesis, research into regulation of the chloroplast rbcL and nuclear RbcS genes that encode this enzyme has lagged behind other plant gene systems. A major characteristic of kranz-type C4 plants is the accumulation of Rubisco only within chloroplasts of internalized bundle sheath cells that surround the leaf vascular centers. In plants that utilize the less common single cell C4 system, Rubisco accumulates only within one type of dimorphic chloroplasts localized to a specific region of leaf chlorenchyma cells. Understanding regulatory processes that restrict Rubisco gene expression to only one cell type or chloroplast type is a major focus of C4 research. Regulatory steps may include transcriptional, post-transcriptional, and post-translational processes.