Matt Johnson

biorxiv.orgA 13-subunit c-ring in the Chlamydomonas chloroplast ATP synthase lowers the H⁺/ATP cost of carbon fixationThe chloroplast F1Fo ATP synthase is a rotary motor that converts the light-driven proton-motive force into the chemical energy of ATP. The number of c-subunits in its rotor fixes the number of proton...

6 Sept

Great to share our new preprint on Chlamy’s chloroplast ATP synthase at 2.2 Å we see 13 c subunits, a modified redox regulation and a complete Grotthuss proton wire 🦠☀️ www.biorxiv.org/content/10.6...

Matt Johnson reposted

nature.comDisequilibrium between chloroplast proton motive force and ATP levels in Arabidopsis - Nature PlantsA fluorescent ATP biosensor reveals that chloroplast ATP levels remain unchanged in Arabidopsis mutants with a much weaker proton gradient, showing that cyclic electron transport protects photosynthes...

Please to share our paper in @natplants.nature.com showing that PGR5 is not required for ATP augmentation in Arabidopsis chloroplasts @profmattjohnson.bsky.social @schwarzlanderlab.bsky.social www.nature.com/articles/s41...

Matt Johnson reposted

Plant Energy Biology Lab

@schwarzlanderlab.bsky.social

50% PMF🪫keeps ATP at 100%🔋 www.nature.com/articles/s41... @natplants.nature.com CET provides ∆pH for photoprotection, while the redox balance is most likely handled by the malate valve 🍃☀️ Based on elegant in vivo ATP biosensing by @gustaf23.bsky.social & @profmattjohnson.bsky.social

Gustaf Degen@gustaf23.bsky.social

For 20 yrs textbook view: linear electron flow can't make enough ATP for CO₂ fixation, so plants use cyclic electron transfer (CET) to top it up. Today in @natplants.nature.com we measured ATP directly inside living chloroplasts — and that story doesn't hold. www.nature.com/articles/s41...

Bottom line: CET's primary job isn't topping up ATP. It builds the ΔpH that protects the photosynthetic apparatus and tunes carbon fixation. [ENDs]

And the original ATP/NADPH imbalance? We favour exporting excess reducing equivalents from the chloroplast — as the main route to balancing the 1.28-vs-1.5 mismatch, rather than augmenting ATP via CET. A model that now needs testing.

The deeper puzzle: why doesn't ATP synthase just make more ATP when pmf is high? It seems to be held back — "metabolic control" of the enzyme above a threshold ATP level, probably via stromal Pi (oligomycin, which raises Pi, overrides it). The chloroplast protects its ΔpH excess!

the "excess" ΔpH from CET isn't for making more ATP — it's for regulation... photosynthetic control (PCON) at cyt b₆f and NPQ, protecting PSI and PSII. Lose it, and pgr5's photoinhibition, fluctuating-light sensitivity and oscillations follow — from lost ΔpH, not ATP starvation.

So we have a real disequilibrium: thylakoid pmf and stromal ATP are uncoupled. Just 50% of WT pmf sustains ~100% of the ATP. If ATP isn't what CET is for — then what is it for?

On pH specifically: the lower ΔpH in pgr5 would, if anything, make the stroma slightly more acidic and bias the sensor to underestimate ATP. So a WT-level reading in pgr5 is the conservative outcome — it can't be a pH-quenching artefact.

Could it be a sensor artefact? The sensor's Kd shifts with temp (kept ≤22.5 °C); it's pH-insensitive across the stromal range (7.0–8.0); it has ample dynamic range left (ATP/Mg²⁺ titrations); and DCMU abolishes the signal — this is genuinely photosynthetic ATP.

At matched light and saturating CO₂, that dark-decay rate is the same in WT and pgr5. Same standing ATP and the same consumption rate. The equal levels aren't masking a hidden shortfall in turnover.

Objection 3 — the sharp one: equal levels could hide lower flux. Perhaps pgr5 just turns ATP over more slowly. So we used the post-illumination dark decay of MgATP²⁻ — how fast ATP falls once photophosphorylation stops — as an in-system readout of CBB ATP demand.

Objection 2: maybe mitochondria import ATP to prop up the chloroplast (as happens in Chlamydomonas). We blocked mitochondrial ATP synthase with oligomycin. No difference between WT and pgr5 chloroplast ATP. Mitochondrial rescue ruled out.

Objection 1: maybe the other CET pathway (NDH) is quietly compensating. So we removed both — the pgr5 ndho double mutant. pmf falls to ~50% of WT… and MgATP²⁻ is still unchanged. Knocking out both CET routes doesn't touch ATP levels.

In pgr5 mutants, pmf is only 50–75% of wild type — a large deficit. Yet stromal MgATP²⁻ is completely unchanged. Half the proton motive force, the same ATP. Losing PGR5-CET simply does not lower chloroplast ATP.

To test it we expressed the FRET ATP biosensor ATeam1.03-nD/nA in the Arabidopsis chloroplast stroma. Rather than inferring ATP from gas exchange or fluorescence, we can now read stromal MgATP²⁻ directly, in vivo, in real time.

jobs.york.ac.ukJobs - The University of York

The logic: LET delivers ~1.28 ATP per NADPH, but the Calvin–Benson–Bassham cycle demands 1.5. CET — mainly via PGR5 — is thought to make the extra proton motive force (pmf) to close that gap. This is the central bioenergetic dogma of oxygenic photosynthesis.

Matt Johnson reposted

Jamie Blaza

@jnb-lab.bsky.social

10 Aug

Permanent academic position as a Lecturer in cryo-ET open at York. We are looking for someone to lead a research program making the most of the stunning advances occurring in cryo-ET. It's a research and teaching post but with a focus on research in the early years. jobs.york.ac.uk/vacancy/lect...

sheffield.ac.ukBBSRC Sponsored Postdoc Position

9 Aug

Why supercomplexes? 🌱☀️🦠 🚨New 3 year Postdoc opportunity 🚨 A BBSRC sponsored project using single molecule AFM to interrogate ephemeral interactions between ET proteins in respiration and photosynthesis Join our diverse team and Apply here: sheffield.ac.uk/photosynthes...

Matt Johnson reposted

6 June

Pleased to share our preprint on “Loss of PSAE redirects PGRL1 to photosystem I and enhances PGR5-dependent cyclic electron transfer in Arabidopsis” @profmattjohnson.bsky.social @sheffieldpps.bsky.social www.biorxiv.org/content/10.6...

12 Nov 2025

Our new preprint 🚨🌱☀️on flourescent biosensing of ATP levels in chloroplasts in vivo shows disequilibrium between proton motive force and ATP levels. We show PGR5 dependent cyclic electron transfer does not augment ATP/NADPH ratios @gustaf23.bsky.social 🙌 www.biorxiv.org/cgi/content/...

Matt Johnson reposted

Ben Engel

@cellarchlab.com

25 Sept 2025

Time for a thread!🧵 How different is the molecular organization of thylakoids in “higher” plants🌱? To find out, we teamed up with @profmattjohnson.bsky.social to dive into spinach chloroplasts with #CryoET ❄️🔬. Curious? ..Read on! #TeamTomo #PlantScience 🧪 🧶🧬 🌾 elifesciences.org/articles/105... 1/🧵

rdcu.beStructure, regulation and assembly of the photosynthetic electron transport chainNature Reviews Molecular Cell Biology - The electron transfer chain in chloroplast thylakoid membranes uses solar energy to produce NADPH and ATP, which power carbon fixation into biomass. This...

21 May 2025

Pleased to share my very general review of Photosynthesis now published in Nature Reviews Mol Cell Biol 🌞🌱 rdcu.be/em1lz Hopefully a useful primer for Postgrad and undergrad students

Matt Johnson reposted

Plants, Photosynthesis and Soil

@sheffieldpps.bsky.social

8 May 2025

Replying to @sheffieldpps.bsky.social

2. Towards climate-change resilient crops: unravelling relationships between CO2 assimilation and ATP production led by @profmattjohnson.bsky.social Power photosynthesis for climate-smart crops. Investigate CO₂ uptake + ATP production. bit.ly/4m5BZ8X #PlantScience #AcademicSky

bit.lyTowards climate-change resilient crops by unravelling the relationship between CO2 assimilation and ATP production at University of Sheffield on FindAPhD.comPhD Project - Towards climate-change resilient crops by unravelling the relationship between CO2 assimilation and ATP production at University of Sheffield, listed on FindAPhD.com

Matt Johnson reposted

academic.oup.comTethering ferredoxin-NADP+ reductase to photosystem I promotes photosynthetic cyclic electron transferThe location of the key photosynthetic enzyme FNR impacts the partitioning of photosynthetic electrons between the linear and cyclic electron transport pat

3 Mar 2025

Finally! After a lot of hard work our paper on tethering FNR to PSI in Chlamy is out in @theplantcell.bsky.social @sheffieldpps.bsky.social @profmattjohnson.bsky.social academic.oup.com/plcell/advan...

Matt Johnson reposted

Ryo Yokoyama

@yokoyama-ryo.bsky.social

19 Dec 2024

A family of NADPH/NADP+ biosensors reveals in vivo dynamics of central redox metabolism across eukaryotes www.nature.com/articles/s41... @naturecomms.bsky.social

nature.comA family of NADPH/NADP+ biosensors reveals in vivo dynamics of central redox metabolism across eukaryotes - Nature CommunicationsThis article presents NAPstars, a family of genetically-encoded biosensors that enable real-time monitoring of NADP redox dynamics across species. The sensors reveal robust NADP redox regulation, cell...

Matt Johnson reposted

Plants, Photosynthesis and Soil

@sheffieldpps.bsky.social

29 Nov 2024

Replying to @sheffieldpps.bsky.social

Determining role of FNR location in photoprotection of photosystem I https://buff.ly/4imFBBM Life depends on photosynthesis; you will study a key photoprotective regulatory mechanism controlling electrical current flow between photosystems matt.johnson@sheffield.ac.uk @profmattjohnson.bsky.social

Matt Johnson reposted

woj_wie

@wojwie.bsky.social

biorxiv.orgMolecular architecture of thylakoid membranes within intact spinach chloroplastsThylakoid membranes coordinate the light reactions of photosynthesis across multiple scales, coupling the architecture of an elaborate membrane network to the spatial organization of individual protei...

This one was delayed for a while… apologies to the musicians. Collab with Matt, Will and Lorna (over on Twitter). And a great dev effort from Lorenz @lorenzlamm.bsky.social. Ofc @cellarchlab.com team. Comment if you want to help. #teamthylakoid www.biorxiv.org/content/10.1...

Matt Johnson reposted

Ben Engel

@cellarchlab.com

It took us seven years, but our collaboration with @profmattjohnson.bsky.social on the molecular architecture of plant thylakoids is finally online. Check it out! #PlantScience #TeamTomo 🧪🔬🧶🧬🌾

woj_wie@wojwie.bsky.social

🥳New cryo tomography Preprint ☀️🌱🔬Molecular architecture of thylakoid membranes within intact spinach chloroplasts. doi.org/10.1101/2024.1… Proud to be part of this great work with @cellarchlab.com @wojwie.bsky.social @sheffieldpps.bsky.social

Two great #PhDposition available in the Photosynthesis Research Group at Sheffield 🌞🌱🦠 Pls RT tinyurl.com/5yhajrpp tinyurl.com/4nsdu45s Come and join us!

Matt Johnson reposted