Biology subjects

Fleming, G.

Publications and source records attributed to Fleming, G..

3 recordsLinked to original sources

bioRxiv2024

Resolving an unconventional non-photochemical quenching signature at the light-to-dark transition

Non-photochemical quenching (NPQ) protects photosynthetic organisms via diverse molecular players contributing at varying timescales. However, in the absence of one of the largest contributors to NPQ, energy-dependent quenching (qE), we observe an unusual but universal phenomenon: a transient increase in quenching in the dark following high light exposure. To mechanistically interrogate this light-to-dark (LtD) NPQ phenotype, we performed chlorophyll fluorescence lifetime snapshot measurements across a diverse array of Arabidopsis mutant backgrounds and chemical treatments. We found that the electrochemical gradient across the thylakoid membrane is essential for this phenomenon. Through analysis of higher-order Arabidopsis mutants, we also found that LtD NPQ is independent of the known forms of photoprotective NPQ, as well as the major and minor light-harvesting complexes (LHCII). Our results point to LtD NPQ as a photoinhibition (qI)-related, reaction center quenching with implications for photoprotection in fluctuating light.

plant biology↗

bioRxiv2024

In vivo analysis of the relationship between CP26 and qE-type NPQ via higher-order Arabidopsis cp26 mutants

CP26 is a monomeric minor light-harvesting complex of PSII (LHCII) protein that connects major LHCII trimers to the PSII core in photosynthetic thylakoid membranes. Previous studies have proposed that CP26 is not only involved in light harvesting but could also be involved in non-photochemical quenching (NPQ). Here, we analyzed higher-order Arabidopsis cp26 mutants using biophysical and pharmacological approaches to investigate the nature of NPQ and its relationship to known NPQ regulators (PSII subunit S (PsbS), the xanthophyll-converting enzyme VDE and the pH gradient across the thylakoid membrane). Maximum PSII quantum efficiencies (Fv/Fm) and chlorophyll fluorescence lifetimes in the dark were significantly lower in cp26 mutants, confirming that CP26 deficiency leads to a sustained quenched state even in the absence of light. Destabilized PSII-LHCII supercomplexes as observed with native PAGE analysis are the likely cause for this pre-quenched state, without other antenna proteins being able to rescue this phenotype. Further analyses revealed that cp26 mutants exhibit modest (single mutant) to highly significant (double mutants) reductions in overall NPQ capacity, which do not directly rely on PsbS and VDE (although the effect is more pronounced when these qE components are altered) but depend on thylakoid lumen acidification and protonation of protein residues. Together, these results show that the NPQ component lacking in cp26 mutants acts independently of qE and qZ and is induced in a slower phase of NPQ induction that most likely relies on pH-dependent conformational changes.

plant biology↗

bioRxiv2022

Interplay between LHCSR proteins and state transitions governs the NPQ response in intact cells of Chlamydomonas during light fluctuations.

Photosynthetic organisms use sunlight as the primary energy source to fix CO2. However, in the environment, light energy fluctuates rapidly and often exceeds saturating levels for periods ranging from seconds to hours, which can lead to detrimental effects for cells. Safe dissipation of excess light energy occurs primarily by non-photochemical quenching (NPQ) processes. In the model green microalga Chlamydomonas reinhardtii, photoprotective NPQ is mostly mediated by pH-sensing light-harvesting complex stress-related (LHCSR) proteins and the redistribution of light-harvesting antenna proteins between the photosystems (state transition). Although each component underlying NPQ has been documented, their relative contributions to the dynamic functioning of NPQ under fluctuating light conditions remains unknown. Here, by monitoring NPQ throughout multiple high light-dark cycles with fluctuation periods ranging from 1 to 10 minutes, we show that the dynamics of NPQ depend on the frequency of light fluctuations. Mutants impaired in the accumulation of LHCSRs (npq4, lhcsr1, and npq4lhcsr1) showed significantly less quenching during illumination, demonstrating that LHCSR proteins are responsible for the majority of NPQ during repetitive exposure to high light fluctuations. Activation of NPQ was also observed during the dark phases of light fluctuations, and this was exacerbated in mutants lacking LHCSRs. By analyzing 77K chlorophyll fluorescence spectra and chlorophyll fluorescence lifetimes and yields in a mutant impaired in state transition, we show that this phenomenon arises from state transition. Finally, we quantified the contributions of LHCSRs and state transition to the overall NPQ amplitude and dynamics for all light periods tested and show that both processes interact to facilitate NPQ during light fluctuations. We further assess the role of LHCSRs in cell growth under various periods of fluctuating light. These results highlight the dynamic functioning of photoprotection under light fluctuations and open a new way to systematically characterize the photosynthetic response to an ever-changing light environment. One sentence summaryThe roles of LHCSR and STT7 in NPQ vary with the light fluctuation period and duration of light fluctuation.

plant biology↗