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

Abstract

Summary The phosphorylation of photosystem II (PSII) and its antenna (LHCII) proteins has been studied, and its involvement in state transitions and PSII repair is known. Yet, little is known about the phosphorylation of photosystem I (PSI) and its antenna (LHCI) proteins. Here, we applied proteomics analysis to generate a 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 and PSI–LHCI protein degradation products in these cells, to estimate the light‐induced damage to PSI–LHCI. Our work revealed the phosphorylation of 17 of 22 PSI–LHCI subunits. The analyses detected the extensive phosphorylation of the LHCI subunits Lhca6 and Lhca7, which is modulated by growth light intensity. Other PSI–LHCI subunits were phosphorylated to a lesser extent, including PsaE, where molecular dynamic simulation proposed that a phosphoserine stabilizes ferredoxin binding. Additionally, we show that HL‐grown cells accumulate less oxidative damage and degradation products of PSI–LHCI proteins, compared with LL‐grown cells. The significant phosphorylation of Lhca6 and Lhca7 at the interface with other LHCI subunits suggests a physiological role during photosynthesis, possibly by altering light‐harvesting characteristics and binding of other subunits.

A high-light tolerant alga from the desert is protected from oxidative stress by NPQ-independent responses

“…The proteomics analysis suggested that in addition to the robust downregulation of LHCII and marked accumulation of carotenoid in HL-grown cells (Levin et al, 2021;, SOD and GPX, and potentially CBR, play a role in considerably reducing ROS accumulation and oxidative damage in HL-grown cells. In agreement with this hypothesis, we have recently reported that HL-grown cells accumulate fewer PSI protein degradation products compared to LL-grown cells, suggesting they are better protected from oxidative stress (Levin et al, 2024).…”

“…Chlorella ohadii is a green micro-alga that thrives in the desert, where it is exposed to extremely high light intensities (Treves et al, 2013; Levin et al, 2021). Accordingly, C. ohadii is highly tolerant to photoinhibition (Treves et al, 2016; Levin et al, 2023; Levin et al, 2024). It has been found that the adaptation of C. ohadii to HL involves marked changes in the thylakoids of which the most pronounced are the large size reductions in the PSII antenna, the LHCII, as well as the massive accumulation of carotenoids and several photoprotective proteins (Levin et al 2021, 2023).…”