Chloroplasts: Genetic Machinery and Regulatory Mechanisms in Plant Function and Adaptation

Plants rely on chloroplasts for photosynthesis and metabolic functions as their genomes developed through endosymbiotic events with cyanobacteria. Next-generation sequencing breakthroughs have exposed structural differences in chloroplast genomes among plant species, which demonstrate the essential function of these genomes in environmental stress adaptation. Chloroplast transcription is governed by two RNA polymerases: Photosynthetic genes are transcribed by PEP, while non-photosynthetic genes are transcribed by NEP, with nuclear factors controlling both processes. The stability and functionality of RNA depend on posttranscriptional modifications, including RNA editing and splicing, which pentatricopeptide-repeat (PPR) proteins and RNA-binding enzymes drive forward. Light-regulated translation within chloroplasts happens through a bacterial-like 70S ribosome that incorporates components from both plastid and nuclear origins. The process of ribosomal pausing plays a critical role in achieving correct protein folding as well as the assembly of photosynthetic complexes. The complex regulatory molecular mechanisms associated with chloroplast gene expression and translation that promote plant growth and stress adaptations are discussed in this chapter.