Chapter 27 - Chloroplast RNA Processing and Stability

Abstract

This chapter focuses on the processing, degradation, and stability of chloroplast mRNAs. First, there is a discussion of the processing of the uniquely discontinuous 23S rRNA. The stable nature of chloroplast mRNAs signifies that transcription and translation in the organelle are not tightly coupled as in prokaryotes, and there is extensive post-transcriptional control of gene expression. Notable reviews on these and related topics are included. Chloroplast RNA processing is explained with a broad overview of 23S rRNA processing, and 5’ pre-mRNA processing. An analysis of the role of specific c regions in the 5’UTR on petD processing is discussed in the section on polycistronic mRNA processing, and of psbB in the section on cis-acting elements in mRNA stability. Stability and 5’ processing appear to be closely linked for this mRNA. A number of nuclear mutants have been isolated are discussed. The mechanism that determines the distinct half-lives of different chloroplast mRNAs remains to be elucidated. It should also be noted that most of the mentioned studies focused on mRNAs coding for photosynthetic proteins; it remains to be seen if these principles will apply to genes for translation and other aspects of chloroplast biology.