Chloroplast Synthesis Under the GUN

Abstract

The chloroplast, the light-converting energy factory of the plant cell, is a complex assemblage of proteins, of which only a portion are actually encoded within the chloroplast genome. The nucleus and the chloroplast thus must carry on a highly coordinated conversation not only to supply the chloroplast with its requisite components, but also to coordinate chloroplast function with other aspects of the cell's development and physiology. Encoded by the nucleus but resident in the plastid, the GUN4 protein is key to chlorophyll synthesis. Larkin et al. now find that GUN4 functions by controlling the synthesis of a signaling intermediate, Mg-protoporphyrin IX, through its actions on the Mg chelatase enzyme. R. M. Larkin, J. M. Alonso, J. R. Ecker, J. Chory, GUN4, a regulator of chlorophyll synthesis and intracellular signaling. Science 299, 902-906 (2003). [Abstract] [Full Text]