Ancient intraflagellar transport machinery controls unique spatial distribution of phototropin in an evolutionary important non-flagellated vegetative stage of terrestrial alga
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Abstract
Intraflagellar transport (IFT) is a conserved trafficking system in eukaryotes that moves proteins along microtubules. It is best known for its essential role in building and maintaining cilia and flagella. Intriguingly, several IFT components are still found in organisms that no longer possess flagella, raising important questions about their original functions and how they may have been repurposed during evolution. The filamentous alga Klebsormidium nitens , positioned at the base of the streptophyte lineage, offers a valuable model for exploring this transition. Here, we investigate the IFT machinery in K. nitens and its relationship with the blue-light photoreceptor phototropin. Comparative genomic analyses show that key IFT-A and IFT-B components are retained, despite the complete loss of flagella in vegetative state. Cellular detection and immunofluorescence studies revealed the presence and localisation of IFT components, interestingly, their co-localization with phototropin. Notably, IFT-139 and IFT-20 strongly co-localize with phototropin at plasma membrane-associated regions. Phototropin overlapping localization (plasma membrane associated) with conserved phospho-adaptor protein 14-3-3, pointing to a phosphorylation-dependent signaling network. Unlike in Chlamydomonas reinhardtii , where these proteins localize to flagella, their interaction in K. nitens occurs independently of cilia presence. Together, these results evidenced that IFT components were retained and repurposed early in streptophyte evolution and might support phototropin localization and signalling, revealing an ancestral, non-ciliary role for the IFT system.
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c.
Amazing that you got so many antibodies to work in these cells! I'm wondering if you did any controls to check for bleed between channels in your microscopy?
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new functions
This is really interesting work showing the conservation of this system even beyond flagellated organisms! In C. reinhardtii, the IFT system is typically thought of as being involved in flagellar transport. However, it also mediates transport to the eyespot along rootlet microtubules, with phototropin being an example of a cargo trafficked to a non-flagellar destination inside the cell. I think it may be useful to compare the functions you've found to this rootlet trafficking to better understand how conserved this non-flagellar function might be.
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phototropins can dynamically relocalize, showing partial redistribution to the cytosol or to distinct membrane subdomains
This image looks very cool! Did you look at localization under different light conditions to see if it changed? I think that would be interesting to see but also a nice way to test your antibody.
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Phototropin operates within a signalling network in Klebsormidium nitens is evolutionarily conserved, yet little rewired
This heading is a bit hard to follow.
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vesicle-mediated intracellular trafficking
Are the vesicle transported on microtubule tracks? I'd love to know a bit more about how phototropins are transported to and from the membrane in land plants (if it's known).
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eyespot
You could point out that IFT-mediated transport to the eyespot happens inside of the cell on rootlet microtubules in Chlamydomonas?
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Introduction
Really great and thorough intro, but it may be nice to break it into paragraphs to make it a bit easier to read.
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