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A good example that sequence conservation can sometimes be deceiving: A-ARF and B-ARF are highly homologous in the degron region, but the extent of degradation and its integration into the auxin response system have greatly diversified (7/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

Using a conditional stable B-ARF, Martijn showed that excess stabilization is detrimental throughout development. This work identifies degradation to be critical for B-ARF function, and B-ARF degradation to be critical for normal development (6/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

So, A-ARF degradation may not be critical, but what about B-ARF? We had reported that loss of its degradation disturbed development of young plants, but what about other stages of development? We systematically mapped degradation and found the B-ARF to be degraded throughout the life cycle (5/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

So, while A/B-ARFs share the same ancestral gene, and are strongly conserved, their degradation has diversified. Martijn next explored the biological relevance of A-ARF degradation and found little to no effect of degron mutation
(4/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

Martijn first identified the essential degron residues in the B-ARF, and next showed that mutating the key degron residue in the A-ARF mildly stabilises the protein - while it dramatically stabilizes the B-ARF (3/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

He used the minimal Marchantia auxin response system, that uses a single A-class (auxin-regulated activator) and a single B-class (competitive antagonist of A-class). He had already shown that both are degraded, but it was unclear if both use the same degron, or what its relevance is (2/7)

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Dolf Weijers @dolfweijers.bsky.social · Sep 5

Recently, both our team and the Richardson/Estelle/Strader teams showed that ARF transcription factors are actively degraded. In this new preprint, Martijn de Roij explores the requirements and relevance of ARF degradation (1/7)

bioRxiv Plant Bio @biorxiv-plants.bsky.social · Sep 5

Diversification of functional requirements for proteolysis of Auxin Response Factors https://www.biorxiv.org/content/10.1101/2025.09.03.673984v1

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

Thanks Keith! Indeed, some of this work was based on expensive equipment, but really mist of it is not. There are new tools (such as chemical dyes that report cellular mechanics), that are very new, but most methods/tools have been around for some years

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

We conclude that this fern passes its body axis onto its progeny through tissue mechanics. We are very excited about this finding and keen to explore in the future. Is this really all there is? What are the mediators? How does this relate to bryophytes and seed plants? Lots to explore! (17/17)

Dolf Weijers @dolfweijers.bsky.social · Sep 1

Second, low concentrations of a MT-depolymerizing drug cause abnormal embryo polarization. Third, tissue ablations showed that the notch-rhizoid axis is essential, but the lateral regions are not. (16/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

Nonetheless, Sjoerd made a number of observations that support the role of mechanics in guiding embryo orientation: First, we could identify the minimal anatomic requirements to be just the notch of dividing cells juxtaposed to neighboring, growing cells. (15/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

Here things become tricky…Ceratopteris is an emerging model and there are very few genetic tools for validating hypotheses. Also, the thin, haploid maternal tissue is very fragile, making perturbations difficult…(14/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

So, can it be that simple? Topology of maternal tissue sets up a stress pattern that orients zygote division, which – coupled to regular division patterns and deterministic embryogenesis – aligns axes of mother and progeny? (13/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

In collaboration with Luis Alonso Baez and Thorsten Hamann (Brillouin microscopy) and Joris Sprakel (molecular rotors), Sjoerd could confirm the requisite stiffness patterns. Also, microtubules showed the predicted orientation patterns. (12/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

And sure enough…when assuming that dividing cells and growing cells have different cell wall stiffness, a stress pattern emerges from tissue topology that predicts the divisions as observed in the zygote. (11/17)

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Dolf Weijers @dolfweijers.bsky.social · Sep 1

Sjoerd next asked if perhaps tissue mechanics might guide division orientation and embryo polarization. Why? Well, stress patterns guide microtubules, which bias division orientation in other systems. Sjoerd teamed up with Jasper van der Gucht, who developed FEM models of fern gametophytes. (10/17)

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