Participation of nuclear genes in chloroplast gene expression

The expression of the plastid genome is dependent on a large number of nucl eus-encoded factors. Some of these factors have been identified through bio chemical assays, and many others by genetic screens in Arabidopsis, Chlamyd omonas and maize. Nucleus-encoded factors function in each step in plastid gene expression, including transcription, RNA editing, RNA splicing, RNA pr ocessing, RNA degradation, and translation. Many of the factors discovered via biochemical approaches play general roles as components of the basic ge ne expression machinery, whereas the majority of those identified by geneti c approaches are specifically required for the expression of small subsets of chloroplast genes and are involved in post-transcriptional steps. Some o f the nucleus-encoded factors may play regulatory roles and modulate chloro plast gene expression in response to developmental or environmental cues. T hey may also serve to couple chloroplast gene expression with the assembly of the protein products into the large complexes of the photosynthetic appa ratus. The convergence of biochemical approaches with those of classical an d reverse genetics, and the contributions from large scale genomic sequenci ng should result in rapid advances in our understanding of the regulatory i nteractions that govern plastid gene expression. (C) 2000 Societe francaise de biochimie et biologie moleculaire / Editions scientifiques et medicales Elsevier SAS.