Cryo-electron tomography of the onion cell wall shows bimodally oriented cellulose fibers and reticulated homogalacturonan networks.
Cryo-electron tomography of the onion cell wall shows bimodally oriented cellulose fibers and reticulated homogalacturonan networks.
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洋葱细胞壁的冷冻电子断层扫描显示双峰取向的纤维素纤维和网状homogalacturonan网络。
DOI：
10.1016/j.cub.2022.04.024
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发表时间：
2022-06-06
期刊：
影响因子：
9.2
通讯作者：
Meyerowitz, Elliot
中科院分区：
文献类型：
--
作者：
Nicolas, William J.;Faessler, Florian;Dutka, Przemyslaw;Schur, Florian K. M.;Jensen, Grant;Meyerowitz, Elliot
植物细胞的一个标志是它们的细胞壁。它们保护细胞免受环境和高膨压的影响，并通过其机械和化学性质的动力学介导形态发生。壁是复杂的多糖结构。虽然它们的生物化学组成是众所周知的，但不同的组分如何在细胞壁的体积中组织并相互作用还不清楚，但这是细胞壁机械特性的关键。为了研究植物细胞壁的超微结构，我们通过冷冻聚焦离子束铣削（冷冻FIB铣削）和冷冻电子断层扫描（冷冻ET）在近天然状态下成像洋葱（洋葱）鳞茎的壁。这使得纤维素纤维原位的高分辨率可视化成为可能。我们揭示了密集的纤维领域的共存，沐浴在一个网状矩阵，我们称之为“网格”，这是更丰富的细胞壁的内表面。纤维在细胞壁的所有深度处采用规则的双峰角分布，并根据它们的取向成束，在细胞壁内形成层。与此同时，采用同型半乳糖醛酸（HG）特异性酶消化，我们观察到的变化，在网格，这表明它是-至少部分-由HG果胶。我们提出了以下模型来构建远轴表皮初生细胞壁：细胞在相对于细胞长轴的-45 °和+45°处沉积连续的纤维素纤维层，并在质膜附近分泌周围富含Hg的网格，然后迁移到细胞壁的更远区域。纤维素纤维根据它们的取向聚集，它们采用双峰角分布，它们被集中在细胞壁表面的网格包围。使用冷冻电子断层扫描以高分辨率显现初级白色洋葱细胞壁。细胞壁内的纤维素纤维的精细组织的特点，并确定为homogalacturonan果胶的网状特征被揭露。
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. The cellulose fibers cluster according to their orientation They adopt a bimodal angular distribution They are bathed by a meshing that concentrates at the surface of the cell wall The meshing is made of homogalacturonans Nicolas et al. used cryo-electron tomography to visualize the primary white onion cell wall at high resolution. The fine organization of the cellulose fibers within the cell wall is characterized, and a mesh-like feature identified as being homogalacturonan pectin is uncovered.
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