Photosynthetic directed endosymbiosis to investigate the role of bioenergetics in chloroplast function and evolution
Bidhan Chandra De, Jason E. Cournoyer, Yang-le Gao, Catherine L. Wallace, Stanley Bram, Angad P. Mehta
Abstract
Cyanobacterial photosynthesis (to produce ATP and NADPH) might have played a pivotal role in the endosymbiotic evolution to chloroplast. However, rather than meeting the ATP requirements of the host cell, the modern-day land plant chloroplasts are suggested to utilize photosynthesized ATP predominantly for carbon assimilation. This is further highlighted by the fact that the plastidic ADP/ATP carrier translocases from land plants preferentially import ATP. Here, we investigate the preferences of plastidic ADP/ATP carrier translocases from key lineages of photosynthetic eukaryotes including red algae, glaucophytes, and land plants. Particularly, we observe that the cyanobacterial endosymbionts expressing plastidic ADP/ATP carrier translocases from red algae and glaucophyte are able to export ATP and support ATP dependent endosymbiosis, whereas those expressing ADP/ATP carrier translocases from land plants preferentially import ATP and are unable to support ATP dependent endosymbiosis. These data are consistent with a scenario where the ancestral plastids may have exported ATP to support the bioenergetic functions of the host cell. Cyanobacterial bioenergetics may have driven chloroplast evolution. Here, the authors show that cyanobacterial endosymbionts expressing plastidic ADP/ATP carrier translocases from red algae and glaucophyte support photosynthesis-driven bioenergetic endosymbiosis, but not those from green land plants.