Abstract
In the chloroplasts of photosynthetic organisms, the conversion of light energy into chemical energy through photosynthesis is essential for photoautotrophic growth. However, the conversion of excess light energy into thermal energy by non-photochemical quenching (NPQ) is important to avoid reactive oxygen species generation and maintain efficient photosynthesis. In the unicellular green alga Chlamydomonas reinhardtii, NPQ as a photoprotective mechanism is activated through wavelength-specific light signaling pathways mediated by the phototropin (blue light) and UVR8 (ultra-violet light, UV) photoreceptors. NPQ-dependent photoprotection improves cell survival under high-light conditions; however, the biological significance of photoprotection activated by different light qualities remains poorly understood. Here, we demonstrate that NPQ-dependent photoprotection is activated more rapidly by UV than visible light. We found that the induction of gene and protein expression related to photoprotection is significantly faster and greater in magnitude under UV treatment compared to that under blue- or red-light treatment. Furthermore, the action spectrum of UV-dependent induction of photoprotective factors implies that Chlamydomonas senses UV-A, whereas the model dicot plant Arabidopsis thaliana senses UV-B for induction of photoprotective responses. Therefore, we hypothesize that Chlamydomonas uses UV-A for the induction of preemptive photoprotection prior to the photoprotection response activated by visible light in the hydrosphere.
Competing Interest Statement
The authors have declared no competing interest.