Thread by @ehaswell

Here I offer a distraction from the terrible news coming from all directions this week—our new preprint! Read on if you like #mechanobiology #plantbiology #piezo channels #vacuoles or #moss. . . Thoughts/questions/RTs are welcome! 1/n biorxiv.org/content/10.110…

We study mechanosensitive ion channels in plants, and one of the big questions we want to answer is how this mesmerizing 🤓class of proteins has been tailored through evolution to the unique mechanical environment of the plant 🌱 cell. 2/10

So, a few years ago we began an effort to study the plant homologs of the famous PIEZO channel, which is a MAJOR mechanosensory cation channel in animals. In this preprint, we describe the evolution, genetics & cell biology of PIEZO channels in moss, or Physcometrium patens. 3/10

TAKE HOME MESSAGE: Moss PIEZOs have diverged from known animal homologs both in terms of function and subcellular location. 🐭🌱🤯. Below are the deets in 6 tweets! 4/10

1, The evolutionary history of these channels is very dynamic. Across eukaryotes, PIEZO genes have undergone repeated, independent duplication and reduction events. Extant plant species have anywhere from 1-3 homologs encoded in their genomes. 5/10

2, Moss is SUCH a cool 😎 model system! We were able to make knock-outs, GFP fusions, and even single point gain-of-function mutations ALL in the endogenous genomic locus 🧬. And it’s mostly a single cell layer thick, so microscopy is a snap 🔬. #mossome 6/10

3, Ivan, Ryan, and CJ found that moss PIEZOs are required for normal growth, cell shape and size of the tip-growing caulonemal cells AND for normal cytoplasmic calcium transients after hypo-osmotic swelling. 7/10

4, Moss PIEZOs localize to the vacuolar (not the plasma) membrane. In retrospect, this makes sense—they can still mediate cytoplasmic calcium transients, just from the vacuole (a huge calcium store) instead of the extracellular space. 8/10

5, Moss PIEZOs also regulate vacuole morphology. Loss-of-function alleles lead to large expanded vacuoles in tip-growing caulonemal cells, while gain-of-function alleles lead to a huge proliferation of internal vacuolar membrane, sometimes laminated and sometimes in bubbles. 9/10

6, We speculate that, in response to vacuolar membrane tension, moss PIEZOs increase the surface volume of vacuolar membranes. Maybe a tubule-like vacuole in the tip allows exploratory cells to grow more efficiently, and/or to better adapt to local changes in environment? 10/10

AND, to make things even MORE exciting, here is a report from @ardemp ‘s group on PIEZO in Arabidopsis!
biorxiv.org/content/10.110…