Dataset Information

Comparison of the photoprotection mechanism in Chlorella Ohadii and Chlamydomonas reinhardtii

ABSTRACT: Light is the driving force of photosynthesis. However, excessive light can be harmful. Photoinhibition, or lightinduced photodamage, 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 ohadii is a green microalga, 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 (LHCSR), PSII protein phosphorylation and state transitions are entirely absent or were barely detected in C. ohadii.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Chlorella Ohadii Chlamydomonas Reinhardtii

SUBMITTER: Oded Kleifeld

LAB HEAD: Gadi Schuster

PROVIDER: PXD038706 | Pride | 2023-05-08

REPOSITORIES: Pride

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Dataset's files

Source:

			Action	DRS
	Chlamy_MF2_Phos.zip	Other
	File_List_Chlamy_Phospho.txt	Txt
	File_List_Ohaddii_Phospho.txt	Txt
	Ohadii_MF2_Phos.zip	Other
	Seq77612_44min_HF.mzML	Mzml

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Project description:Adjustment of gene expression during acclimation to stress conditions, such as bright light, in the cyanobacterium Synechocystis sp. PCC 6803 depends on four group 2 M-OM-^C factors (SigB, SigC, SigD, SigE). A M-bM-^HM-^FsigCDE strain containing the stress responsive SigB as an only functional group 2 M-OM-^C factor appears twice as resistant to photoinhibition of photosystem II (PSII) as the control strain. Microarray analyzes of the M-bM-^HM-^FsigCDE strain indicated that 77 genes in standard conditions and 79 genes in high light were differently expressed compared to the control strain. Analysis of possible photoprotective mechanisms revealed that high carotenoid content and up-regulation of the photoprotective flavodiiron operon flv4-sll0218-flv2 protected PSII in M-bM-^HM-^FsigCDE, while up-regulation of pgr5-like, hlipB or isiA genes in the mutant strain did not offer particular protection against photoinhibition. The photoinhibition resistance was lost if M-bM-^HM-^FsigCDE was grown in high CO2 where carotenoid and Flv4-Sll0218-Flv2 contents were low. Additionally, photoinhibition resistance of the M-bM-^HM-^FrpoZ strain (lacking the omega subunit of RNA polymerase) with very high carotenoid but only low Flv4-Sll0218-Flv2 content supported the importance of carotenoids in PSII protection. Carotenoids likely protect mainly via quenching of singlet oxygen but efficient non-photochemical quenching in M-bM-^HM-^FsigCDE might offer some additional protection. Comparison of photoinhibition kinetics in control, M-bM-^HM-^FsigCDE and M-bM-^HM-^FrpoZ strains showed that protection by the flavodiiron operon was most efficient during the first minutes of high-light illumination. Cells from cyanobacteria Synechocystis sp. PCC 6803 named as control strain (CS) and group 2 sigma factor mutant M-NM-^TsigCDE (A730=1, 40 mL) were harvested directly from standard growth conditions (continuous illumination at the PPFD of 40 M-BM-5mol m-2s-1, 32M-BM-0C, ambient CO2) or after 30-min illumination a PPFD 750 M-BM-5mol m-2s-1. From three to four independent experiments were performed at each conditions.

Dataset Information

Comparison of the photoprotection mechanism in Chlorella Ohadii and Chlamydomonas reinhardtii

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