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Genetic, Genomics, and Responses to Stresses in Cyanobacteria: Biotechnological Implications
Hypothesis

Are Cyanobacteria an Ancestor of Chloroplasts or Just One of the Gene Donors for Plants and Algae?

Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan
Academic Editors: Denis Baurain and Luc Cornet
Received: 26 March 2021 / Revised: 8 May 2021 / Accepted: 25 May 2021 / Published: 27 May 2021
Chloroplasts of plants and algae are currently believed to originate from a cyanobacterial endosymbiont, mainly based on the shared proteins involved in the oxygenic photosynthesis and gene expression system. The phylogenetic relationship between the chloroplast and cyanobacterial genomes was important evidence for the notion that chloroplasts originated from cyanobacterial endosymbiosis. However, studies in the post-genomic era revealed that various substances (glycolipids, peptidoglycan, etc.) shared by cyanobacteria and chloroplasts are synthesized by different pathways or phylogenetically unrelated enzymes. Membranes and genomes are essential components of a cell (or an organelle), but the origins of these turned out to be different. Besides, phylogenetic trees of chloroplast-encoded genes suggest an alternative possibility that chloroplast genes could be acquired from at least three different lineages of cyanobacteria. We have to seriously examine that the chloroplast genome might be chimeric due to various independent gene flows from cyanobacteria. Chloroplast formation could be more complex than a single event of cyanobacterial endosymbiosis. I present the “host-directed chloroplast formation” hypothesis, in which the eukaryotic host cell that had acquired glycolipid synthesis genes as an adaptation to phosphate limitation facilitated chloroplast formation by providing glycolipid-based membranes (pre-adaptation). The origins of the membranes and the genome could be different, and the origin of the genome could be complex. View Full-Text
Keywords: chloroplast origin; cyanobacterial endosymbiosis; glycolipids; host-directed chloroplast formation; peptidoglycan; Paulinella chromatophore; phylogenetic analysis chloroplast origin; cyanobacterial endosymbiosis; glycolipids; host-directed chloroplast formation; peptidoglycan; Paulinella chromatophore; phylogenetic analysis
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MDPI and ACS Style

Sato, N. Are Cyanobacteria an Ancestor of Chloroplasts or Just One of the Gene Donors for Plants and Algae? Genes 2021, 12, 823. https://0-doi-org.brum.beds.ac.uk/10.3390/genes12060823

AMA Style

Sato N. Are Cyanobacteria an Ancestor of Chloroplasts or Just One of the Gene Donors for Plants and Algae? Genes. 2021; 12(6):823. https://0-doi-org.brum.beds.ac.uk/10.3390/genes12060823

Chicago/Turabian Style

Sato, Naoki. 2021. "Are Cyanobacteria an Ancestor of Chloroplasts or Just One of the Gene Donors for Plants and Algae?" Genes 12, no. 6: 823. https://0-doi-org.brum.beds.ac.uk/10.3390/genes12060823

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