iiinova — where your digital self keeps evolving

Michael Hothorn @structplantbio.bsky.social · 07/10/2026

Today’s department seminar by @pascalalbanese.bsky.social @cea.fr Grenoble on protein - protein interactions in photosynthetic complexes

060

Michael Hothorn @structplantbio.bsky.social · 18/09/2026

There is "thinking outside the box", and then there is "thinking outside the boxer". Nice work from @agroscope.bsky.social nph.onlinelibrary.wiley.com/doi/10.1002/...

060

Michael Hothorn @structplantbio.bsky.social · 16/09/2026

Very nice PPRM2026 ( Plant Peptide Receptor Meeting) closes in Freising. Organised by @julien-gronnier.bsky.social , @isabelmonte.bsky.social and @kpkinase.bsky.social

1207

Michael Hothorn @structplantbio.bsky.social · 05/08/2026

Out in @natplants.nature.com, mapping of brassinosteroid chemical features required for (1) receptor binding, (2) ligand positioning and (3) co-receptor recruitment. Fantastic work by Alberto Caregnato & @hmchen93.bsky.social and our friends in Olomouc. Funding:@snf-fns.ch -> doi.org/10.1038/s414...

15831

Michael Hothorn @structplantbio.bsky.social · 23/06/2026

Es ist schade, dass ihr Studenten den Überfluss und den Luxus nicht so recht kennet, in dem ihr lebet. Aber es ist auch mir so gegangen, als ich noch Student war.

210

Michael Hothorn @structplantbio.bsky.social · 12/06/2026

Very happy with today’s PhD defence by Alberto Caregnato. Amazing quantitative biochemistry, crystallography and cryoEM. Well done Alberto, it was a pleasure working with you. Big thanks to @hillerlab.bsky.social, Andreas Boland and @romanulm.bsky.social

1132

Michael Hothorn @structplantbio.bsky.social · 10/06/2026

Fantastic last seminar before his well deserved retirement by Philippe Reymond @unil.bsky.social on the signaling immune responses following insect cell deposition on plant leaves. A technical tour de force & exciting findings.

0176

Michael Hothorn @structplantbio.bsky.social · 04/06/2026

This work nicely quantifies a major issue in our universities: "In higher education, administrative costs have risen much faster than instruction and research costs (4). MIT Faculty grew by only 9.2% between 1985 and 2023, while administrative staff grew by 189%." www.pnas.org/doi/10.1073/...

87743

Michael Hothorn @structplantbio.bsky.social · 21/05/2026

Team effort from @fxrico.bsky.social, Oded, Pierre, Andrea, @hmchen93.bsky.social, Larissa now out in @pnas.org The Kelch phosphatase BSU1 is a PP1-like serine/threonine phosphatase involved in cell cycle regulation, not a tyrosine phosphatase in brassinosteroid signaling 👍 doi.org/10.1073/pnas...

24521

Michael Hothorn @structplantbio.bsky.social · 14/05/2026

"Eine Hauptursache der Armut in den Wissenschaften ist meist eingebildeter Reichtum. Es is nicht das Ziel, der unendlichen Weisheit eine Tür zu öffnen, sondern eine Grenze zu setzen dem unendlichen Irrtum."

021

Michael Hothorn @structplantbio.bsky.social · 23/03/2026

New method paper from Alberto Caregnato and former PhD student @hohmannulrich.bsky.social. A tailored crystallisation screen for plant receptor kinase ectodomains, with examples from our lab and from @cellsensing.bsky.social. Check it out: www.biorxiv.org/content/10.6...

04224

Michael Hothorn @structplantbio.bsky.social · 17/02/2026

Very nice genetic dissection of the roles of BSK kinases in brassinosteroid signaling by Wenqiang Tang's lab. bsk-u (ko for BSK1 1, 2, 3, 4, 5, 6, 7, 8, 10, 11 & 12) really looks like a bri1 null mutant and can be rescued by over-expressing BSK3. nph.onlinelibrary.wiley.com/doi/epdf/10....

0178

Michael Hothorn @structplantbio.bsky.social · 10/02/2026

@hohmannulrich.bsky.social, your new address is freeing up quite some characters ;-)

011

Michael Hothorn @structplantbio.bsky.social · 09/02/2026

I thought of myself as a structural biologist and biochemist. Apparently not...

000

Michael Hothorn @structplantbio.bsky.social · 08/02/2026

Very nice & complete review on inositol pyrophosphate metabolism and signaling in plants by Ricardo Giehl @leibnizipk.bsky.social and @gabrielschaaf.bsky.social @unibonn.bsky.social . Also includes an impressive to-do-list...

185

Michael Hothorn @structplantbio.bsky.social · 07/01/2026

@fxrico.bsky.social deleted the single BSU1 gene in Marchantia, resulting in a mass of undifferentiated cells & strong patterning defects. Cell cycle markers are highly active in the thallus. Our data point to a function for Kelch phosphatases in the cell cycle not in BR signaling (6/6).

051

Michael Hothorn @structplantbio.bsky.social · 07/01/2026

In Andrea’s structure the C-terminal tail of BSU1 is phosphorylated and bound to the active site. Andrea and Pierre showed that this phosphorylation is caused by the CDK1-cyclin-CKS1 complex, very similar to PP1, where no structure is available. The phosphorylation inhibits BSU1 activity (5/6).

100

Michael Hothorn @structplantbio.bsky.social · 07/01/2026

Oded and Felix Rico generated CRISPR/Cas9 knock-out mutants of all Kelch phosphatases in Arabidopsis. These mutants have a fertility defect, suggesting a function in embryo development, many more stomata than wild type, but wild type-like BR responses. (4/6)

110

Michael Hothorn @structplantbio.bsky.social · 07/01/2026

BSU1 was originally identified in an activation tagging screen in the weak BR receptor mutant bri1-5. Oded Pri-Tal found, to our surprise, that also phosphatase-dead versions of the enzyme can rescue the bri1-5 mutant. A mutant in the RVxF substrate binding groove does not rescue. (3/6)

110

Michael Hothorn @structplantbio.bsky.social · 07/01/2026

A crystal structure from Andrea Moretti of the Kelch phosphatase BSU1 reveals that it looks virtually identical to PP1, a Ser/Thr phosphatase involved in cell cycle regulation. Consistently, Pierre Raia could show that BSU1 is an efficient Ser/Thr, not a tyrosine phosphatase in vitro. (2/6)

110

Michael Hothorn @structplantbio.bsky.social · 12/12/2025

My PhD supervisor Klaus Scheffzek (1958-2025) has passed away. tinyurl.com/3dcm73p6 Klaus was an expert structural biologist with degrees in physics and biology, an excellent scientist, a great teacher, and pianist. He made key contributions to G-protein signaling @embl.org @mpi-mr.bsky.social

130

Michael Hothorn @structplantbio.bsky.social · 05/12/2025

Nice work by the Mayer and @jessenlab.bsky.social labs out in @elife.bsky.social. Inositol pyrophosphates regulate the vacuolar inorganic polyphosphate and Pi pools, allowing Pi to be re-imported into the cytosol when cells experience phosphate starvation. elifesciences.org/articles/108...

053

Michael Hothorn @structplantbio.bsky.social · 29/11/2025

This project has been a joint effort with the Fiedler and Panse labs, supported by an @snf-fns.ch Sinergia grant and the @erc.europa.eu. The work from my lab was done by PhD student Kristina Sturm, postdocs Oded Pri-Tal, @fxrico.bsky.social, @hmchen93.bsky.social and technician Larissa Broger (6/6).

020

Michael Hothorn @structplantbio.bsky.social · 29/11/2025

Interestingly, only the α-subunit, not the α2β2 CK2 holoenzyme, is regulated by PP-InsPs in vitro. Genetic analyses in Arabidopsis and Marchantia indicate that α-subunits can act independently of β-subunits, underscoring the physiological relevance of PP-InsP-mediated regulation of CK2. (5/6)

100

Michael Hothorn @structplantbio.bsky.social · 29/11/2025

Mutations in the CK2 PP-InsP binding site alter flowering time in Arabidopsis. In parallel, the Panse lab showed that this site is essential for CK2 function in yeast (4/6).

100

Michael Hothorn @structplantbio.bsky.social · 29/11/2025

Notably, we found the α-subunit of casein kinase 2 (CK2) interact with PP-InsPs and with the PP-InsP kinase VIH2. CK2 binds InsP6/7/8 with micromolar affinity. PP-InsP binding reduces substrate phosphorylation by occupying the kinase’s basic substrate-binding surface (3/6).

100

Michael Hothorn @structplantbio.bsky.social · 29/11/2025

The first major surprise was the prevalence of deeply conserved protein complexes among the identified interactors, including the spliceosome, the ribosome, the CFlm complex, and numerous signaling proteins such as protein kinases. (2/6).

131

Michael Hothorn @structplantbio.bsky.social · 21/11/2025

Very nice application of our constitutive active BIR3-RK chimera from @hohmannulrich.bsky.social (doi.org/10.1105/tpc....) to dissect the contribution of ERECTA to vascular differentiation. doi.org/10.1073/pnas.... Congrats to @lauraragni.bsky.social @bertderybel.bsky.social @bayerlab.bsky.social

0103

Michael Hothorn @structplantbio.bsky.social · 25/10/2025

By the @cellsensing.bsky.social and Zipfel labs: The plant receptor kinase HSL3 senses a cyclic, disulfide-bond stabilized peptide phytocytokine. www.biorxiv.org/content/10.1...

02916

Michael Hothorn @structplantbio.bsky.social · 17/10/2025

A lot of pressure on the different grant schemes, and pretty much independent of career stage.

02721

Michael Hothorn @structplantbio.bsky.social · 30/09/2025

Amazing work by the Santiago lab @unil.bsky.social. The malectin-LRR receptor kinase IGP1 senses cello-oligomers to alert the plant immune system & enhance disease resistance. Very nice discovery & mechanism. www.biorxiv.org/content/10.1...

03825

Michael Hothorn @structplantbio.bsky.social · 17/09/2025

Today’s department seminar on SnRK1 by Elena Baena Gonzalez from @ox.ac.uk

041

Michael Hothorn @structplantbio.bsky.social · 26/08/2025

Complete transport cycle of human XPR1, regulated by InsP8 and KIDINS220 @cp-molcell.bsky.social doi.org/10.1016/j.mo...

042

Michael Hothorn @structplantbio.bsky.social · 25/08/2025

Unexpected hit in the list of the most highly cited papers of the 21st century.

000

Michael Hothorn @structplantbio.bsky.social · 25/08/2025

Cool stuff, discovery of protein oliogophosphorylation by the Fiedler lab @fmp-berlin.de @natchem.nature.com. www.nature.com/articles/s41... Now what if NME1 is indeed the missing eukaryotic inorganic polyphosphate kinase?

042

Michael Hothorn @structplantbio.bsky.social · 11/08/2025

Very nice cryo-EM structure of rice PHT1 phosphate transporter by Zhu Liu's lab in Wuhan. www.biorxiv.org/content/10.1...

021

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

But perhaps the nicest finding from Alberto was that the exact positioning of the ligand in the receptor is absolutely critical for co-receptor recognition. Based on this we can now accurately predict how a bioactive BR needs to look like, and how receptor antagonists can be designed.

130

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

We also found that BRL2 actually is a bona fide BR receptor with a distinct ligand spectrum.

100

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

Next, we mutated the entire hormone binding pocket in BRI1 and assayed the mutants for BR binding and their ability to rescue a bri1 null mutant. It turns out the binding site has amazing structural plasticity with only few contacts being critical.

100

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

We next solved 10 crystal structures of BRI1 and BRL3 in complex with different BRs. It turns out the configuration of the tail not the steroid ring core is critical for binding.

100

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

We synthesized 15 different natural and synthetic BRs and quantified their interaction with BRI1, BRL1 and BRL3. All three receptors can sense chemically diverse C27, C28 and C29 BRs with high affinity.

100

Michael Hothorn @structplantbio.bsky.social · 09/08/2025

Our latest on brassinosteroid signaling: Ligand binding spectrum, specificity & selectivity of all BR receptors in Arabidopsis. By @albertocaregnato.bsky.social , @hmchen93.bsky.social and our great chemistry collaborators Mirek Kvasnica, Jana Oklestkova and Mirek Strnad.

15529

Michael Hothorn @structplantbio.bsky.social · 07/07/2025

Nice idea, bringing kinases and different phosphatase candidates in close proximity, by using a PYL ABA receptor, the ABI1 phosphatase and ABA to trigger the interaction. www.nature.com/articles/s42...

000

Michael Hothorn @structplantbio.bsky.social · 20/06/2025

Nice lab hike in the Swiss Jura yesterday with @fxrico.bsky.social @hmchen93.bsky.social & the rest of the team.

061

Michael Hothorn @structplantbio.bsky.social · 28/05/2025

Very nice department seminar today by Chloe Zubieta @cnrs.fr Grenoble on the mechanism of ELF3 LLPS. A very complete analysis using many different biophysical methods combined with reverse genetics.

000

Michael Hothorn @structplantbio.bsky.social · 20/05/2025

Finally, a productive afternoon ...

010

Michael Hothorn @structplantbio.bsky.social · 07/05/2025

Today’s department seminar by Ute Höcker from university of Cologne. Nice to see a bit of sun on a gloomy Wednesday.

040