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Cryo-electron tomography of the onion cell wall shows bimodally oriented cellulose fibers and reticulated homogalacturonan networks

Nicolas, William J. and Fäßler, Florian and Dutka, Przemyslaw and Schur, Florian K. M. and Jensen, Grant and Meyerowitz, Elliot (2022) Cryo-electron tomography of the onion cell wall shows bimodally oriented cellulose fibers and reticulated homogalacturonan networks. Current Biology, 32 (11). pp. 2375-2389. ISSN 0960-9822. PMCID PMC9240970. doi:10.1016/j.cub.2022.04.024.

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One hallmark of plant cells is their cell wall. They protect cells against the environment and high turgor and mediate morphogenesis through the dynamics of their mechanical and chemical properties. The walls are a complex polysaccharidic structure. Although their biochemical composition is well known, how the different components organize in the volume of the cell wall and interact with each other is not well understood and yet is key to the wall’s mechanical properties. To investigate the ultrastructure of the plant cell wall, we imaged the walls of onion (Allium cepa) bulbs in a near-native state via cryo-focused ion beam milling (cryo-FIB milling) and cryo-electron tomography (cryo-ET). This allowed the high-resolution visualization of cellulose fibers in situ. We reveal the coexistence of dense fiber fields bathed in a reticulated matrix we termed “meshing,” which is more abundant at the inner surface of the cell wall. The fibers adopted a regular bimodal angular distribution at all depths in the cell wall and bundled according to their orientation, creating layers within the cell wall. Concomitantly, employing homogalacturonan (HG)-specific enzymatic digestion, we observed changes in the meshing, suggesting that it is—at least in part—composed of HG pectins. We propose the following model for the construction of the abaxial epidermal primary cell wall: the cell deposits successive layers of cellulose fibers at −45° and +45° relative to the cell’s long axis and secretes the surrounding HG-rich meshing proximal to the plasma membrane, which then migrates to more distal regions of the cell wall.

Item Type:Article
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URLURL TypeDescription Information S1 S2 S3 Script CentralArticle Paper
Nicolas, William J.0000-0001-5970-8626
Fäßler, Florian0000-0001-7149-769X
Dutka, Przemyslaw0000-0003-3819-1618
Schur, Florian K. M.0000-0003-4790-8078
Jensen, Grant0000-0003-1556-4864
Meyerowitz, Elliot0000-0003-4798-5153
Alternate Title:Bimodally oriented cellulose fibers and reticulated homogalacturonan networks - A direct visualization of Allium cepa primary cell walls
Additional Information:© 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( Received 10 February 2022, Revised 17 March 2022, Accepted 8 April 2022, Available online 3 May 2022. This work was supported by the Howard Hughes Medical Institute (HHMI) and grant R35 GM122588 to G.J. and the Austrian Science Fund (FWF) P33367 to F.K.M.S. We thank Noé Cochetel for his guidance and great help in data analysis, discovery, and representation with the R software. We thank Hans-Ulrich Endress for graciously providing us with the purified citrus pectin and Jozef Mravec for generating and providing the COS488 probe. Cryo-EM work was done in the Beckman Institute Resource Center for Transmission Electron Microscopy at Caltech. This article is subject to HHMI’s Open Access to Publications policy. HHMI lab heads have previously granted a nonexclusive CC BY 4.0 license to the public and a sublicensable license to HHMI in their research articles. Pursuant to those licenses, the author accepted manuscript of this article can be made freely available under a CC BY 4.0 license immediately upon publication. Author contributions: W.J.N. conceived the experiments, prepared the samples, acquired and analyzed the data, performed the data exploration, wrote the manuscript, and drew the figures. F.F. wrote the custom scripts that allowed collection of the per-fiber parameters, helped in data analysis, and participated in writing/correction of the manuscript. P.D. performed the fiber averages, helped in the data analysis relative to the fiber averages, and participated in the correction of the manuscript. F.K.M.S. participated in experimental design of the data analysis, funding, and the correction of the manuscript. G.J. participated in guidance, experimental design, funding, and correction/advising on writing the manuscript. E.M. participated in guidance, experimental design, funding, and correction/advising on writing the manuscript. The authors declare no competing interests. Data and code availability: The tilt series, tomograms,.mdoc and.rawtlt used for the data analysis are available upon request. Representative tomograms have been deposited in the Electron Microscopy Data Bank (EMDB) under accession codes EMDB: EMD-26564, EMD-26569, EMD-26568, and EMD-26570. The three cellulose fiber averages have been deposited in EMDB under accession codes EMD-26571, EMD-26572, and EMD-26573. See key resources table for individual description. The bash script used to generate the meshing subtracted maps and quantify the fiber/meshing ratios was deposited on ResearchGate ( DOIs are lister in the key resources table.
Funding AgencyGrant Number
Howard Hughes Medical Institute (HHMI)UNSPECIFIED
NIHR35 GM122588
FWF Der WissenschaftsfondsP33367
Subject Keywords:onion; cryo-tomography; cell wall; cellulose; pectins
Issue or Number:11
PubMed Central ID:PMC9240970
Record Number:CaltechAUTHORS:20220202-980591000
Persistent URL:
Official Citation:William J. Nicolas, Florian Fäßler, Przemysław Dutka, Florian K.M. Schur, Grant Jensen, Elliot Meyerowitz, Cryo-electron tomography of the onion cell wall shows bimodally oriented cellulose fibers and reticulated homogalacturonan networks, Current Biology, Volume 32, Issue 11, 2022, Pages 2375-2389.e6, ISSN 0960-9822,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113213
Deposited By: Tony Diaz
Deposited On:02 Feb 2022 16:37
Last Modified:05 Jul 2022 18:47

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