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A blue-light photoreceptor mediates the feedback regulation of photosynthesis

​​An international consortium coordinated by researchers from the Cell​ & Plant Physiology Laboratory, the National Institute for Basic Biology in Japan and Humboldt University in Germany, has deciphered the molecular links that​ exist in microalgae between the perception of light, its use for photosynthesis and protection against light stress. These results, which open new perspectives in the study of the light trafficking in photosynthetic organisms, are published in the journal Nature

Published on 4 October 2016
Green microalgae, the ancestors of land plants, are microscopic organisms mainly living in the planet waters. Like plants, they are able of performing photosynthesis, a complex metabolic process that converts CO2 into biomass and oxygen using the energy of sunlight. Light is not only the source of energy that fuels photosynthesis but also acts as source of information. Thanks to specific sensors, called photoreceptors, algae respond to the light colour moving towards or against the light (phototaxis), regulating their cell division and other fundamental processes. When light intensity becomes very strong (i.e. under full sunlight) it can become toxic, producing reactive oxygen species and cell damage. To avoid this, photosynthetic organisms can actively decrease their light absorption capacity via photoprotective mechanisms that dissipate the excess light as heat, avoiding cell damage.

In a collaborative work with Japanese and German, researchers at the Light-Photosynthesis & Metabolism team (Cell & Plant Physiology Laboratory) revealed a link between these three functions of the light. They shown that the green alga Chlamydomonas reinhardtii uses a specific blue light photoreceptor (phototropin, PHOT) not only to sense the light color 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 (Figure). They propose that the mechanism that brings together light sensing, utilization 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 colonize the land, and eventually disappeared in plants, which are exposed to the full visible spectrum.

Schematic representation of the molecular links between the perception of light, its use for photosynthesis, and protection against the light stress in the microalgae Chlamydomonas reinhardtii.

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