The incredible architectural complexity of plants

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3D image of a molecularly labeled pollen tube of lady’s slipper. The green
3D image of a molecularly labeled pollen tube of lady’s slipper. The green signal shows the web-like structure formed by pectin polysaccharides in conjunction with cell wall protein complexes. This protein-regulated physical arrangement provides a support system for sustained plant cell growth. Ursina Rathgeb DBMV-UNIL
Ensuring growth and development, sometimes sustained, without risking fragility. This is the delicate balance facing plants. The team led by Julia Santiago Cuellar, Associate Professor at the University of Lausanne, has revealed how a judicious arrangement of sugar molecules, like bricks, strengthens the plant wall and enables it to expand without exploding. This discovery has been published in the November 9, 2023 issue of the journal "Science".

Combining extensibility, robustness and protective functions

Plant cells are distinguished by their extraordinary ability to use solar energy to convert atmospheric carbon dioxide (CO2) into sugars. The latter are an inexhaustible source not only of energy, but also of building materials. Like links in a chain, sugars can assemble to form long polymers, known as polysaccharides. Arranged in a complex network around the plasma membrane of plant cells, these polysaccharides help build the cell wall. The cell wall acts both as a protective barrier and as the support for a pressurized, extensible skeleton, giving the plant its rigidity while allowing plant cells to expand. When these cells change shape, grow or divide, they have to remodel their cell wall architecture.

Growth without explosion

One question remains, however: how do plant cells organize their cell wall structure so that they can grow without the risk of exploding? This issue, central to plant biology, lies at the heart of understanding the key mechanisms of plant growth and adaptation to constantly changing environmental conditions.

Unidirectional growth

In a study just published in Science, the group led by Julia Santiago Cuellar , Associate Professor in the Department of Plant Molecular Biology in the Faculty of Biology and Medicine at the University of Lausanne, in collaboration with a group of scientists from the Institut national de la recherche agronomique (INRAE) in Versailles (France), provides some answers. We have identified an active mechanism which, via a protein complex, interacts directly with the polysaccharides of the cell wall, assembling them according to a particular pattern that favours unidirectional expansion", explains the Lausanne-based professor in charge of the research.

Highly resistant web-like fibers

To analyze this process in detail, the scientists used as models the pollen tubes of Arabidopsisthaliana, a fast-growing, single-celled plant structure measuring around 5 um. Their study used a multidisciplinary approach, combining biochemical, genetic and state-of-the-art super-resolution microscopy techniques to dissect the heart of this mechanism both in vitro and in planta.

Our data show how an activated protein complex is responsible for knitting unstructured sugar chains, pectins, into an organized pattern of cross-linked filaments", explains Julia Santiago Cuellar. This three-dimensional arrangement of web-like fibers thus enables the cell walls of pollen tubes to withstand high turgor (growing) pressure by sustaining continuous growth, without exploding. This structure resembles a solid support system, like an explosion-proof water pipe.

Our discovery provides molecular evidence that plant cells orchestrate the appropriate physical and chemical organization of their cell walls to support plant growth and development", comments the biologist.

Towards more sustainable agriculture

Understanding the complex mechanisms by which plants actively shape and remodel their cell walls is a fundamental step in the search for more resistant crops. By creating crops that can adapt and thrive in changing environmental conditions, we can enhance food security, reduce the impact of agriculture on the environment and contribute to a more sustainable future. This idea embodies the intersection of plant biology and biotechnology, at the service of agricultural innovation", concludes Julia Santiago Cuellar.