Chloroplast protein import machinery inherited from green algae to plants clarified
A group of researchers from Institute for Protein Research (IPR) of Osaka University, University of California (USA), and University of Geneva (Switzerland) has clarified that a protein import machinery of chloroplasts plays an important role in green algae, the origin of land plants.
Chloroplasts, important organelles that allow plants and algae to perform photosynthesis by importing some 3000 types of proteins into the chloroplast post-translationally.
Previously, the researchers at Osaka University clarified two translocons, molecular complexes that receive protein substrates for translocation across a membrane: the TIC complex (translocon on the inner chloroplast membrane) complex and the TOC complex (translocon on the outer chloroplast membrane), but their evolutionary origin was not known.
In this study, the researchers discovered a novel large TIC complex in Arabidopsis (Arabidopsis thaliana, the thale cress), termed the “1-MDa complex”, was functionally conserved in green algae Chlamydomonas (Chlamydomonas reinhardtii), known as an ancestor of plants, and played a role of the chloroplast protein import machinery.
It is widely accepted that the origin of most of existing photosynthesis eukaryotes are ancestral eukaryotes that acquired photosynthesis cyanobacterial endosymbiont as the chloroplast billions of years ago.
Since it is said that land plants evolved from green algae and that green algae and land plants are members of the kingdom Plantae, this group’s discovery will lead to the clarification of the process in which chloroplasts evolved into green algae and land plants.
It is anticipated that this group’s achievements will be applied to chloroplast engineering to mass produce beneficial biologically active substance through the metabolic process in which chloroplasts are not involved.
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The article, "Co-expressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts," was published in Proceedings of the National Academy of Sciences (PNAS) at DOI: https://www.pnas.org/doi/full/10.1073/pnas.2014294117.
