About this Research Topic
Plastids are cell organelles present in plants, green and red algae as well as in some non-photosynthetic organisms such as the apicomplexa. Depending on their species- and tissue-specific context they exhibit morphological and biochemical properties of wide variety. In green plant tissues they are the site for photosynthesis and important biochemical pathways including sulfur and nitrogen reduction. In non-green tissues they act as storage organelles for starch and/or are essential for lipid or carotenoid biogenesis. Despite their heterogeneous appearance all plastid types emerged from one and the same monophyletic endosymbiotic event in which a cyanobacteria-like ancestor was taken up by a heterotrophic, mitochondriated eukaryote. One specific remnant of this prokaryotic ancestry is the presence of a fully active genetic system in plastids consisting of a highly polyploid genome, the so-called plastome, as well as a complete machinery to express the information coded on it. This covers DNA polymerases for replication, proteins for DNA organization, RNA polymerases for transcription, multiple processing, stabilisation and maturation enzymes for RNA metabolism as well as 70S ribosomes and a full set of tRNAs for translation. Recent years have uncovered numerous regulatory proteins controlling plastid gene expression in response to internal (developmental) and external (environmental) cues. These regulators and the genetic system are organized in specialized supra-molecular complexes called nucleoids. Fluorescence microscopy revealed that these structures appear as several distinct spots within chloroplasts which are associated to thylakoids. However, appearance and distribution is very dynamic and depends on plastid type and developmental stage. Data from biochemical analyses, proteomics and functional genomics have improved our understanding of the structure, function and regulation of the proteins located in the nucleoids and contributed much to our understanding of plastid gene expression. This Research Topic is dedicated to focus on recent advances in this quickly emerging field of research with a special emphasis on newly discovered proteins.
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