Biology subjects

Levin, G.

Publications and source records attributed to Levin, G..

4 recordsLinked to original sources

bioRxiv2024

The high-light-tolerant desert alga Chlorella ohadii is protected from oxidative stress by a non-photochemical quenching-independent mechanism

Non-photochemical quenching (NPQ) mechanisms are crucial for protecting photosynthesis from photoinhibition in plants, algae, and cyanobacteria, and their modulation is a long-standing goal for improving photosynthesis and crop yields. The current work demonstrates that Chlorella ohadii, a green micro-alga that thrives in the desert under high light intensities which are fatal to many photosynthetic organisms, does not perform nor require NPQ to protect photosynthesis under constant high light. Instead of dissipating excess energy, it minimizes its uptake by eliminating the photosynthetic antenna of photosystem II. In addition it accumulates antioxidants that neutralize harmful reactive oxygen species (ROS) and ramps up cyclic electron flow around PSI. These NPQ-independent responses proved efficient in preventing ROS accumulation and reducing oxidative damage to proteins in high-light-grown cells.

plant biology↗

bioRxiv2023

The protein phosphorylation landscape in photosystem I of the desert algae Chlorella sp.

O_LIThe phosphorylation of photosystem II (PSII) and its antenna (LHCII) proteins has been extensively studied and its involvement in state transitions and PSII repair is well known. Yet, very little is known about the extent and functions of phosphorylation of photosystem I (PSI) and its antenna (LHCI) proteins. C_LIO_LIHere, two proteomics methods were applied to generate a detailed map of the phosphorylation sites of the PSI-LHCI proteins in Chlorella ohadii cells that were grown under low- or extreme high-light intensities (LL and HL). Furthermore, we analyzed the content of oxidized tryptophans in these cell types to estimate light-induced oxidative damage to PSI-LHCI. C_LIO_LIOur work revealed the phosphorylation of 11 out of 22 PSI-LHCI subunits. The analyses detected extensive phosphorylation of the LHCI subunits lhca6 and lhca7. Other PSI-LHCI subunits were phosphorylated to a lesser extent. Additionally, we show the accumulation of oxidatively damaged tryptophans in the psaD subunit of PSI of HL-grown C. ohadii. C_LIO_LIThe significant phosphorylation of lhca6 and lhca7 suggests a physiological role during photosynthesis, possibly by altering light-harvesting characteristics and binding of other LHCI subunits. Moreover, we show that psaD is susceptible to photodamage while LHCI is protected from ROS under HL. C_LI

plant biology↗

bioRxiv2022

A desert green alga that thrives at extreme high-light intensities using a unique photoin-hibition protection mechanism

While light is the driving force of photosynthesis, excessive light can be harmful. Photoinhibition, or light-induced photo-damage, is one of the key processes limiting photosynthesis. When the absorbed light exceeds the amount that can be dissipated by photosynthetic electron flow and other processes, damaging radicals are formed that mostly inactivate photosystem II (PSII). A well-defined mechanism that protects the photosynthetic apparatus from photoinhibition has been described in the model green alga Chlamydomonas reinhardtii and plants. Chlorella oha-dii is a green micro-alga, isolated from biological desert soil crusts, that thrives under extreme high light (HL) in which other organisms do not survive. Here, we show that this alga evolved unique protection mechanisms distinct from those of C. reinhardtii and plants. When grown under extreme HL, significant structural changes were noted in the C. ohadii thylakoids, including a drastic reduction in the antennae and the formation of stripped core PSII, lacking its outer and inner antennae. This is accompanied by a massive accumulation of protective carotenoids and proteins that scavenge harmful radicals. At the same time, several elements central to photoinhibition protection in C. reinhardtii, such as psbS, the stress-related light harvesting complex, PSII protein phosphorylation and state-transitions are entirely absent or were barely detected in C. ohadii. Taken together, a unique photoinhibition protection mechanism evolved in C. ohadii, enabling the species to thrive under extreme-light intensities where other photo-synthetic organisms fail to survive.

plant biology↗

bioRxiv2021

The desert green algae Chlorella ohadii thrives at excessive high light intensities by exceptionally enhancing the mechanisms that protect photosynthesis from photoinhibition

Although light is the driving force of photosynthesis, excessive light can be harmful. One of the main processes that limits photosynthesis is photoinhibition, the process of light-induced photodamage. When the absorbed light exceeds the amount that is dissipated by photosynthetic electron flow and other processes, damaging radicals are formed that mostly inactivate photosystem II (PSII). Damaged PSII must be replaced by a newly repaired complex in order to preserve full photosynthetic activity. Chlorella ohadii is a green micro-alga, isolated from biological desert soil crusts, that thrives under extreme high light and is highly resistant to photoinhibition. Therefore, C. ohadii is an ideal model for studying the molecular mechanisms underlying protection against photoinhibition. Comparison of the thylakoids of C. ohadii cells that were grown under low light versus extreme high light intensities, found that the alga employs all three known photoinhibition protection mechanisms: i) massive reduction of the PSII antenna size; ii) accumulation of protective carotenoids; and iii) very rapid repair of photo-damaged reaction center proteins. This work elucidated the molecular mechanisms of photoinhibition resistance in one of the most light-tolerant photosynthetic organisms and shows how photoinhibition protection mechanisms evolved to marginal conditions, enabling photosynthesis-dependent life in severe habitats. One Sentence HighlightAnalysis of the photosynthetic properties of a desert algae that thrives at extreme high light intensities revealed protection from photoinhibition driven by the remarkable enhancement of three protection mechanisms.

plant biology↗