PTC Circadian Regulation of Chloroplast Gene Transcription: A Review

The chloroplast is the plant cell organelle for photosynthesis, but it is also the location of important biogenetic activities. Chloroplasts have their own genetic system that contain ~100- 250 genes, depending on the species. The functions of these genes are mainly in photosynthesis and genetic functions of the organelle. The expression of chloroplast genes is regulated at every level, including transcription. The regulation of plastid gene expression during the development of etioplasts (or proplastids) into chloroplasts (a.k.a., “greening”) has been well studied. Gene regulation is also critical to mature chloroplasts, and this review focuses on the regulation of chloroplast transcription that is driven by the solar cycle and mediated by the circadian clock. Historical, as well as recent, work with vascular plants and Chlamydomonas are discussed. We have also included brief summaries on plant circadian systems, and the proteins and promoter elements involved in chloroplast transcription. Finally, possible mechanism(s) for circadian regulation of chloroplast transcription are discussed, as is a pers