Intracellular Signaling and Chlorophyll Synthesis

Abstract

The chloroplast proteome is encoded by genes that reside in both the chloroplast and the nucleus. This separation of genetic material necessitates a system for coordinating the expression of genes that reside in each compartment. Because the overwhelming majority of genes that encode chloroplast proteins reside in the nucleus, the regulation of nuclear genes by developmental and environmental cues plays a dominant role in chloroplast development and function. However, the chloroplast is not indifferent to its own protein composition. In fact, the chloroplast generates signals that have dramatic effects on the expression of nuclear genes that encode particular chloroplast proteins. Currently it is known that plastids produce at least a few distinct signals during chloroplast development that are required for proper expression of particular nuclear genes that encode components of the photosynthetic machinery. In response to certain environmental signals, mature chloroplasts send additional signals that regulate nuclear gene expression. The molecular nature of most of these plastid-to-nucleus signaling pathways is not well established. However, a number of studies have suggested that accumulation of certain chlorophyll precursors within plastids is a signal that regulates nuclear gene expression during chloroplast development and during the diurnal cycle. Future work in this area should provide detailed molecular information on the influence of chlorophyll synthesis and other plastid-localized metabolism on nuclear gene expression and how plants utilize this formof interorganellar communication during their lifecycles.