Abstract
The origin of photosynthetic organelles via endosymbiosis more than 1 Gya ago was a major detonator of eukaryotic diversification. The evolution of a stable endosymbiotic relationship between eukaryotic cells and photosynthetic cyanobacteria involved series of cellular and molecular processes that are not entirely understood. Critical steps towards the evolution of plastids occurred when the host cell gained genetic and metabolic control over the captured cyanobacterium. Proteins recruited from the host repertoire had major roles initiating the metabolite exchange between both symbiotic partners. Concurrently, the relocation of certain cyanobacterial genes into the host nuclear genome was critical to coordinate the division of the endosymbiotic cells and the transit of nuclear-encoded proteins into the novel organelle. This review explores diverse studies that have identified key “endosymbiosis genes” and discusses the putative roles of the encoded proteins during the early evolution of plastids. The understanding of the regulation mechanisms and functions of the “endosymbiosis genes” will shed light on the design of genetic engineering approaches to facilitate endosymbiotic associations.
Highlights
Photosynthesis is the generic name for different photoautotrophic pathways that vary depending on the types of lightharvesting systems, photosynthetic pigments, electron donors (e.g., H2O, H2, S2, H2S, S2O23−) and released byproducts (e.g., O2, S2, H2S) (Bryant and Frigaard, 2006; Blankenship, 2010)
Circa 2 Gya after the appearance of the oxygenic photosynthesis some eukaryotes acquired the photosynthetic metabolism through the establishment of a “permanent” endosymbiotic relationship with cyanobacteria (Hedges et al, 2004; Yoon et al, 2004)
Unlike the case of plants and algae, where several hundreds of genes have been transferred via EGT from the plastid ancestor into the nuclear genome, only 32 chromatophore-derived genes have been identified among thousands of nuclear transcripts of P. chromatophora (Nowack et al, 2011). This minimal estimate of 32 chromatophore-derived genes encodes mainly proteins of relative low molecular weight (≤250 amino acids), including 19 involved in photosynthesis and light-stress responses (Nowack et al, 2011). These results revealed two trends: genes of relatively short length were prone to successful EGT and the encoded proteins, which participate in photosynthesis and light stress responses, were likely important to gain initial control over the endosymbiont autotrophic metabolism (Nowack et al, 2011)
Summary
Reviewed by: Andres Moya, University of Valencia, Spain Natalia Ivanova, Lawrence Berkeley National Laboratory, USA. The origin of photosynthetic organelles via endosymbiosis more than 1 Gya ago was a major detonator of eukaryotic diversification. The evolution of a stable endosymbiotic relationship between eukaryotic cells and photosynthetic cyanobacteria involved series of cellular and molecular processes that are not entirely understood. Critical steps toward the evolution of plastids occurred when the host cell gained genetic and metabolic control over the captured cyanobacterium. Proteins recruited from the host repertoire had major roles initiating the metabolite exchange between both symbiotic partners. The relocation of certain cyanobacterial genes into the host nuclear genome was critical to coordinate the division of the endosymbiotic cells and the transit of nuclear-encoded proteins into the novel organelle. This review explores diverse studies that have identified key “endosymbiosis genes” and discusses the putative roles of the encoded proteins during the early evolution of plastids.
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