Non-photochemical quenching (NPQ, also called qE) is widely present in photosynthetic species. It dissipates excess light energy under adverse growing conditions, thus protecting phototrophs from photodamage. The NPQ systems employed by cyanobacteria, algae, and higher plants are all very different, whereas within a specific phylum, it seems rather conservative. Three types of NPQ systems have been identified so far: they are the blue-green light-sensitive phycobilisome-orange carotenoid protein (OCP) system in cyanobacteria, the low luminal pH-triggered LHCSR/LHCX system in green algae and diatom, and the PsbS-VDE system for higher plants. Despite decades of studies of NPQ from multi-disciplinary aspects, their quenching mechanisms remain controversial. Besides, if there is any novel type of NPQ system, it still needs to be explored. Deciphering the mechanisms of these three identified NPQ systems or searching for new NPQ gene elements or systems is essential for optimizing photosynthesis and further improving crop environmental fitness.
In the first part of this talk, I will review the up-to-date knowns and unknowns about the key players of the NPQ process and how they function together under the frame of NPQ biodiversity, covering an extensive range of photosynthetic species of cyanobacteria, green algae, red algae, glaucophyte, diatom, liverwort, and higher plants. In the second part, I will mainly share two of our recent results in our lab: one is on NPQ in the green alga of Chlamydomonas reinhardtii, in which we have managed to resolve the quencher molecule and unravel the quenching kinetics. The other one is on NPQ in the liverwort of Marchantia polymorpha. We have constructed the knock-out mutants of PsbS and VDE, respectively, and their double mutants. We found that the NPQ traits in liverwort almost mirror the ones in higher plants, showing that the PsbS-VDE NPQ systems had already fully evolved in non-vascular plants.