The unicellular green microalga Botryosphaerella sudetica links plant‐like light protection with an algal lifestyle

Nonphotochemical quenching (NPQ) mechanisms fine-tune light utilisation in the photosynthetic antenna, for example, in response to excess light, to prevent photodamage. NPQ comprises distinct mechanisms, all contributing to photoprotection but acting on different time scales. Preferences for individual mechanisms and NPQ composition are proposed to reflect the organism's lifestyle, especially regarding sessile vs motile styles, with the latter enabling photophobic responses. We analysed photoprotection in the nonmotile, unicellular chlorophycean microalga Botryosphaerella sudetica, belonging to a genus known to form high-light-exposed floating aquatic biofilms. Growth, Chl fluorescence, its nuclear genome, and the expression of photoprotective genes were analysed in comparison with the motile chlorophycean microalga Chlamydomonas reinhardtii. These analyses revealed that B. sudetica is, in contrast to C. reinhardtii, equipped with a constitutive energy-dependent quenching (qE) mechanism based on the constitutive accumulation of protein PSBS, the thylakoid lumen pH-sensor, found throughout the green plant lineage. While qE was the predominant NPQ mechanism in B. sudetica and required zeaxanthin formation, state transitions (qT), which largely contributed to NPQ in C. reinhardtii, played a minor role. These data demonstrate that a core set of NPQ mechanisms conserved in the Viridiplantae is shuffled to meet better the adaptive requirements imposed by the habitat.