In a collaborative work with Japanese and German colleagues the accliphot team light photosynthesis and metabolism has revealed a link between these three functions of the light. We have shown that the green alga Chlamydomonas reinhardti uses a specific blue light photoreceptor (phototropin, PHOT) not only to sense the light colour but also to integrate information about the light intensity, ultimately activating the photoprotective mechanism that dissipates the excess light for photosynthesis in the form of heat (see Figure).
We propose that the mechanism that brings together light sensing, utilisation and dissipation evolved in the ocean, the ancestral environment where photosynthetic organisms evolved, there where blue light dominates the available spectrum. It then contributed to the capacity of photosynthetic organism to colonise the land, and eventually disappeared in plants, which are exposed to the full visible spectrum (Petroutsos et al. 2016)
Schematic representation of the existing molecular links between light perception, photosynthesis and photoprotection in the microalga Chlamydomonas reinhardtii. Blue light is perceived by the LOV domain of the protein phototropin (PHOT). LOV activates the kinase domain (KIN) that transforms the light signal into a biological signal that is transduced (blue arrow) to the nucleus. This signal integrates with a chloroplastic signal (red arrow) that carries information of the amount of light that is absorbed by the cell but not used for photosynthesis. The two signals regulate the transcription of the gene LHCSR3 in the nucleus and the accumulation of the LHCSR3 protein in the choroplast (black arrow). The protein LHCSR3 converts the excess light energy into heat.
Petroutsos D*, Tokutsu R, Maruyama S, Flori S, Greiner A, Magneschi L, Cusant L, Kottke T, Mittag M, Hegemann P, Finazzi G* and Minagawa J*
A blue-light photoreceptor mediates the feedback regulation of photosynthesis.
Nature, 2016, 537(7621): 563-566