β-Cyclocitral Does Not Contribute to Singlet Oxygen-Signalling in Algae, but May Down-Regulate Chlorophyll Synthesis

Abstract

Light stress signalling in algae and plants is partially orchestrated by singlet oxygen (1O2), a reactive oxygen species (ROS) that causes significant damage within the chloroplast, such as lipid peroxidation. In the vicinity of the photosystem II reaction centre, a major source of 1O2, are two β-carotene molecules that quench 1O2 to ground-state oxygen. 1O2 can oxidise β-carotene to release β-cyclocitral, which has emerged as a 1O2-mediated stress signal in the plant Arabidopsis thaliana. We investigated if β-cyclocitral can have similar retrograde signalling properties in the unicellular alga Chlamydomonas reinhardtii. Using RNA-Seq, we show that genes up-regulated in response to exogenous β-cyclocitral included CAROTENOID CLEAVAGE DIOXYGENASE 8 (CCD8), while down-regulated genes included those associated with porphyrin and chlorophyll anabolism, such as tetrapyrrole-binding protein (GUN4), magnesium chelatases (CHLI1, CHLI2, CHLD, CHLH1), light-dependent protochlorophyllide reductase (POR1), copper target 1 protein (CTH1), and coproporphyrinogen III oxidase (CPX1). Down-regulation of this pathway has also been shown in β-cyclocitral-treated A. thaliana, indicating conservation of this signalling mechanism in plants. However, in contrast to A. thaliana, a very limited overlap in differential gene expression was found in β-cyclocitral-treated and 1O2-treated C. reinhardtii. Furthermore, exogenous treatment with β-cyclocitral did not induce tolerance to 1O2. We conclude that while β-cyclocitral may down-regulate chlorophyll synthesis, it does not seem to contribute to 1O2-mediated high light stress signalling in algae.

Profile change of the volatile and non‐volatile compounds in dried or baked laver by photooxidation

“…Laver contains 400–700 mg/100 g chlorophyll (Do Thi & Hwang, 2014), which is a porphyrin ring‐containing green pigment and photosensitizer (Lee et al., 2019). Photochemical autoxidation is promoted by singlet oxygen (Roach et al., 2022) and is accelerated by chlorophyll. Over 60 days, linoleic acid decreased by 2.5 times and oleic acid decreased by two times in laver stored under light conditions compared to laver stored under dark conditions.…”

Chlamydomonas reinhardtii—A Reference Microorganism for Eukaryotic Molybdenum Metabolism

“…All of this has allowed for the development of a number of biochemical, metabolic, and physiological studies that have contributed to the understanding of the structure, function, and regulation of several biological processes [ 17 ]. Among others, the research topics that have used Chlamydomonas as a reference organism include the metabolism of nitrogen [ 18 ], sulfur [ 19 ], phosphorus [ 20 ], amino acid [ 21 ], and lipids [ 22 ], the biosynthesis of carotenoids [ 23 ], starch [ 24 ], heme groups [ 25 ], Fe-S clusters [ 26 ], chlorophyll [ 27 ], and glycerolipids [ 28 ], as well as the function of chaperones [ 29 ], proteases [ 30 ], thioredoxins [ 31 ], and flagella [ 32 ] and the response to different types of stresses [ 33 ].…”

Chlamydomonas reinhardtii a Reference Microorganism for Eukaryotic Molybdenum Homeostasis

“…All of this has allowed for the development of a number of biochemical, metabolic, and physiological studies that have contributed to the understanding of the structure, function, and regulation of several biological processes [17]. Among others, the research topics that have used Chlamydomonas as a reference organism include the metabolism of nitrogen [18], sulfur [19], phosphorus [20], amino acid [21], and lipids [22], the biosynthesis of carotenoids [23], starch [24], heme groups [25], Fe-S clusters [26], chlorophyll [27], and glycerolipids [28], as well as the function of chaperones [29], proteases [30], thioredoxins [31], and flagella [32] and the response to different types of stresses [33].…”