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A look into the formation of centrioles in the first land plants

New study looks into the 3D architecture of centrioles in moss, revealing that these structures are more diverse than previously thought

The recent study published on Current Biology, led by IGC PI Mónica Bettencourt and, then IGC, now ITQB NOVA PI and GREEN-IT member Jörg Becker, delves into the formation of centrioles in the moss Physcomitrium patens, revealing unique details of its architecture. According with the results, even though they are made of the same molecular blocks as animal cells, they mature in a vastly different way.

Mosses, contrary to flowering plants, have mobile sperm cells, which depend on water to move, much like what happens with humans. The mobility is achieved through the tails – the flagellum – which contains centrioles. However, in mosses the two centrioles at the base of the flagella form together, and then separate and elongate in a very different way. Even though the two similar structures are formed at the same time and remain very close to each other, the cell still manages to regulate which one elongates and which does not, leading to a unique symmetry breaking. This is contrary to what happens in animals, where the centrioles are very similar to each other inside each cell. “Most literature claims that plants do not have centrioles and that is it. But centrioles are created without a mold in the sperm cells of some plant species. The organism has never had these structures and simply makes them, in the proper number and place. It almost feels like magic” reveals Sónia Gomes Pereira, first author of the study and recent IGC doctorate.

Through the use of 3D electron tomography, the team was able to get an unprecedented detailed look at the three main stages of centriole development in 3D. The samples were frozen at an extremely low temperature – cryopreservation- and then selected and put on a transmission electron microscope. There, a beam of electrons was transmitted through the sample and, as they interacted, an image was formed. By taking pictures at each degree of inclination of each section, they were able to then mathematically reconstruct the complete structure in 3D.

These studies help us understand how evolution works, especially in the first land plants. And this is the first species where we describe this process”, says Jörg Becker, former IGC principal investigator, now at ITQB NOVA, and GREEN-IT member, which co-led the study. Mosses are crucial to ecosystems, especially newly formed ones, as they stabilize the soil surface, reduce erosion and maintain moisture, by reducing water evaporation, while allowing other plants to grow. “It is crucial to comprehend how they reproduce and live, and from that knowledge build the foundation for future interventions, in case of necessity”, adds the researcher.

Studying a wide variety of organisms, such as the moss Physcomitrium patens, allows to understand the similarities in the process of centriole formation along the tree of life. From conserved molecular blocks, mosses, create centrioles with very unique characteristics in their sperm cells, revealing how plastic evolution can be. In animals, manipulating the molecular building blocks that make up the centriole has constraints—animals without centrioles are unhealthy. “This moss only has them in their sperm, which is a big plus. Since potential defects only appear in these cells, we can cultivate and study them as usual. What we have learned with the advance of genetics and molecular biology, not just microscopy, may open new paths for us to begin understanding how diversity is created”, highlights Mónica Bettencourt Dias, IGC principal investigator and co-leader of the study.


Original paper:

Current Biology | 10.1101/2020.12.21.423647

The 3D architecture and molecular foundations of de novo centriole assembly via bicentrioles.

Sónia Gomes Pereira, Ana Laura Sousa, Catarina Nabais, Tiago Paixão, Alexander J. Holmes, Martin Schorb, Gohta Goshima, Erin M. Tranfield, Jörg D. Becker, Mónica Bettencourt-Dias