Abstract
Marine diatom is a eukaryotic alga fixing 20 % of global CO2. This massive productivity is sustained by their uniquely structured secondary chloroplast. Diatom chloroplasts possess layered thylakoid membranes, comprising of the outer-most girdle lamellae and the inner stroma thylakoid (ST). At the central chloroplast, there is pyrenoid, which is a phase-separated Rubisco condensate interlinked by intrinsically disordered proteins. In diatoms, protein called Pyrenoid Shell (PyShell) shapes and covers the pyrenoid, within which thylakoid traverses along the axis of the pyrenoid core, that is, pyrenoid-penetrating thylakoid (PPT). The PPT lumen specifically harborsθ-type carbonic anhydrase (CA) and the genome editing disruption of this luminalθ-CA re- sulted in a null CCM phenotype, indicating the pivotal role of PPT luminalθ-CA to constitute the “CO2-evolving machinery” for Rubisco in the pyrenoid. The HCO3- supplier for the CO2-evolving machinery is bestrophin (BST) family protein, localized at the ST and/or PPT area. The KO of ST-type PtBST1 suppressed CCM to the level mimicking high CO2 acclimated cells and moderately enhanced NPQ, suggesting that ST-type BST enhances CO2 fixation for CCM, thus thylakoidal linear electron flow, in sacrifice of NPQ. These results indicate that the CO2-evolving machinery in the pyrenoid coordinates CO2 and light utilization efficiency.
https://ror.org/02qf2tx24 
