The Evolution of Photosystem II Subunit S across the Green Lineage
type: CreativeWork
description: Light absorbed by plants can have three different fates: it can be used to drive photosynthetic electron transport, be re-emitted as fluorescence or be dissipated as heat (non-photochemical quenching, NPQ). When light levels are too high, NPQ is an important protective process that prevents damage to membranes and proteins in the chloroplast. In vascular plants, the major trigger of fast-inducing energy-dependent NPQ is the Photosystem II subunit S protein (PsbS), which is activated in response to high light and interacts with photosystem II to cause quenching. Algae and moss, however, are thought to predominantly use another protein to regulate NPQ, the Light Harvesting Complex Stress-Related protein (LHSCR), despite having gene copies of PsbS. Therefore, there has been a broad-scale transition from LHCSR-dependent NPQ to PsbS-dependent NPQ during plant evolution but how and why PsbS became the major trigger of NPQ and whether this required neofunctionalisation is still unclear. To answer these questions, we performed a phylogenetic analysis that uses a newly collected and curated dataset of PsbS sequences corresponding to 1,007 species to analyse both overall structural similarity and the conservation of key residues that have been identified to be important for PsbS function (Chapter 2). We found that PsbS is very well-conserved both at a structural and residue level across the whole green lineage. In fact, 92% of the protein is under negative selection, while only one residue was found to be both under positive selection and undergo recurrent mutations. Based on these findings, we saw no evidence of pronounced sequence changes aligning with PsbS’ rise to become the dominant quenching regulator. To support the theoretical analyses in Chapter 2, we tested functional complementation of PsbS sequences from 11 species across the green lineage via expression in the PsbS-knockout mutant in Arabidopsis thaliana in Chapter 3. Significant restoration of NPQ was observed w…
abstract: Light absorbed by plants can have three different fates: it can be used to drive photosynthetic electron transport, be re-emitted as fluorescence or be dissipated as heat (non-photochemical quenching, NPQ). When light levels are too high, NPQ is an important protective process that prevents damage to membranes and proteins in the chloroplast. In vascular plants, the major trigger of fast-inducing energy-dependent NPQ is the Photosystem II subunit S protein (PsbS), which is activated in response to high light and interacts with photosystem II to cause quenching. Algae and moss, however, are thought to predominantly use another protein to regulate NPQ, the Light Harvesting Complex Stress-Related protein (LHSCR), despite having gene copies of PsbS. Therefore, there has been a broad-scale transition from LHCSR-dependent NPQ to PsbS-dependent NPQ during plant evolution but how and why PsbS became the major trigger of NPQ and whether this required neofunctionalisation is still unclear. To answer these questions, we performed a phylogenetic analysis that uses a newly collected and curated dataset of PsbS sequences corresponding to 1,007 species to analyse both overall structural similarity and the conservation of key residues that have been identified to be important for PsbS function (Chapter 2). We found that PsbS is very well-conserved both at a structural and residue level across the whole green lineage. In fact, 92% of the protein is under negative selection, while only one residue was found to be both under positive selection and undergo recurrent mutations. Based on these findings, we saw no evidence of pronounced sequence changes aligning with PsbS’ rise to become the dominant quenching regulator. To support the theoretical analyses in Chapter 2, we tested functional complementation of PsbS sequences from 11 species across the green lineage via expression in the PsbS-knockout mutant in Arabidopsis thaliana in Chapter 3. Significant restoration of NPQ was observed w…
author: Robijns, Alice
language: eng
keywords: photosynthesis, PsbS, non-photochemical quenching, plant sciences, evolution
license: https://www.repository.cam.ac.uk/bitstreams/e98362d9-0ceb-42bd-8d2c-9d525b3b8f3d/download
license: http://purl.org/NET/rdflicense/allrightsreserved
date published: 2025-09-29
date modified: 2026-07-22T22:23:56Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.123735