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Chilling Upregulates Expression of the PsbS and LhcSR Genes in the Chloroplasts of the Green Microalga Lobosphaera incisa IPPAS C-2047

Vasily V. Ptushenko1,2,a*, Grigorii N. Bondarenko3, Elizaveta N. Vinogradova4,5, Elena S. Glagoleva1,4, Olga V. Karpova4, Oxana S. Ptushenko1,4, Karina A. Shibzukhova1,4, Alexei E. Solovchenko4,6, and Elena S. Lobakova4

1Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

2Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 119334 Moscow, Russia

3Faculty of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia

4Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

5Kurchatov Institute National Research Center, 123182 Moscow Russia

6Pskov State University, 128000 Pskov, Russia

* To whom correspondence should be addressed.

Received October 6, 2022; Revised November 3, 2022; Accepted November 3, 2022
Non-photochemical quenching (NPQ) of excited chlorophyll states is essential for protecting the photosynthetic apparatus (PSA) from the excessive light-induced damage in all groups of oxygenic photosynthetic organisms. The key component of the NPQ mechanism in green algae and some other groups of algae and mosses is the LhcSR protein of the light harvesting complex (LHC) protein superfamily. In vascular plants, LhcSR is replaced by PsbS, another member of the LHC superfamily and a subunit of photosystem II (PSII). PsbS also performs the photoprotective function in mosses. For a long time, PsbS had been believed to be nonfunctional in green algae, although the corresponding gene was discovered in the genome of these organisms. The first evidence of the PsbS accumulation in the model green alga Chlamydomonas reinhardtii in response to the increase in irradiance was obtained only six years ago. However, the observed increase in the PsbS content was short-termed (on an hour-timescale). Here, we report a significant (more than three orders of magnitude) and prolonged (four days) upregulation of PsbS expression in response to the chilling-induced high-light stress followed by a less significant (~ tenfold) increase in the PsbS expression for nine days. This is the first evidence for the long-term upregulation of the PsbS expression in green alga (Chlorophyta) in response to stress. Our data indicate that the role of PsbS in the PSA of Chlorophyta is not limited to the first-line defense against stress, as it was previously assumed, but includes full-scale participation in the photoprotection of PSA from the environmental stress factors.
KEY WORDS: thermal dissipation of light energy, PsbS, LhcSR, high-light stress, chilling acclimation, Chlorophyta

DOI: 10.1134/S0006297922120240