Chloroplast Biogenesis: Control of Plastid Development, Protein Import, Division and Inheritance

Abstract

The chloroplast is a multi-copy cellular organelle that not only performs photosynthesis but also synthesizes amino acids, lipids and phytohormones. The plastid also responds to environmental stimuli such as gravitropism. Biogenesis of chloroplasts is initiated from proplastids in shoot meristems, and involves a series of important events. In the last decade, considerable progress has been made towards understanding various aspects of chloroplast biogenesis at the molecular level, via studies in model systems such as Arabidopsis. This review focuses on two important aspects of chloroplast biogenesis, synthesis/assembly and division/transmission. Chloroplasts originated through endosymbiosis from an ancestor of extant cyanobacteria, and thus contain their own genomes. DNA in chloroplasts is organized into complexes with proteins, and these are called nucleoids. The synthesis of chloroplast proteins is regulated at various steps. However, a majority of proteins are synthesized in the cytosol, and their proper import into chloroplast compartments is a prerequisite for chloroplast development. Fundamental aspects of plastid gene expression/regulation and chloroplast protein transport are described, together with recent proteome analyses of the organelle. Chloroplasts are not de novo synthesized, but instead are propagated from pre-existing plastids. In addition, plastids are transmitted from generation to generation with a unique mode of inheritance. Our current knowledge on the division machinery and the inheritance of plastids is described.

Use of a SPAD-502 meter to measure leaf chlorophyll concentration in Arabidopsis thaliana

“…The particular advantages of this species are well documented, and include its completely-sequenced genome, diminutive stature, and rapid generation time, as well as the availability of extensive collections of insertional mutants such that it is possible to quickly identify a knockout for almost any gene of interest. As a result, a considerable proportion of the chloroplast and plastid research that is undertaken today is conducted using the Arabidopsis model system (Leister 2003;López-Juez 2007;Sakamoto et al 2008). Nonetheless, only a very small number of Arabidopsis studies have employed the SPAD-502 meter, and these have either presented the data in unconverted arbitrary units (Stettler et al 2009) or utilized a crude scaling factor to estimate actual chlorophyll content (Takami et al 2010).…”

How life changes itself: The Read–Write (RW) genome

“…Thus, most of the proteins needed for plastid and mitochondrial function are synthesized from nuclear transcripts in the cytoplasm and have to be reimported into the organelle where they act [112]. …”

Fast Retrograde Signaling in Response to High Light Involves Metabolite Export, MITOGEN-ACTIVATED PROTEIN KINASE6, and AP2/ERF Transcription Factors in Arabidopsis

“…ROS are detoxified by the water-water cycle in an either ascorbate-dependent enzymatic process (Asada 1999(Asada , 2000 or ascorbate-independent pathway with peroxiredoxins Muthuramalingam et al, 2009). Like the majority of chloroplast proteins, all antioxidant enzymes are encoded in the nucleus (Abdallah et al, 2000;Sakamoto et al, 2008). To coordinate gene expression with metabolic needs, a retrograde signaling network originates from the chloroplast and transmits information on the metabolic state to the nucleus.…”