Abstract
In this study, the function of light-harvesting proteins (LHC/FCP) in the marine diatom Chaetoceros gracilis was investigated. Among them, Lhcx1 was found to be essential for non-photochemical quenching (NPQ). The knockout of the Lhcx1 gene via genome editing almost completely abolished the ability to induce NPQ. The Lhcx1 knockout mutant (lhcx1), which lacks NPQ, showed the capacity to acclimate by activating various high-light protection systems inherent to C. gracilis, resulting in higher PSII activity compared to the wild type. This increase in PSII activity was enhanced by the addition of carbon dioxide in the lhcx1 mutant, suggesting that both upstream changes in the light-harvesting system and downstream adaptation of electron sinks in the electron transport chain play crucial roles in high-light acclimation in C. gracilis. These findings represent the first demonstration that genetic manipulation of diatom light-harvesting capacity can improve the efficiency of light energy conversion in photosynthesis. As a marine diatom, C. gracilis would have evolved multiple photoprotective mechanisms in order to adapt to highly fluctuating oceanic environments. The present study suggests that these defense systems are interconnected and exhibit a high degree of regulatory flexibility in response to environmental changes.
