Boyce Thompson Institute, Ithaca, NY, USA.
Advanced Electron Microscopy Facility, University of Chicago, Chicago, IL, USA.
Nat Plants. 2019 Feb;5(2):194-203. doi: 10.1038/s41477-019-0364-5. Epub 2019 Feb 8.
During arbuscular mycorrhizal (AM) symbiosis, cells within the root cortex develop a matrix-filled apoplastic compartment in which differentiated AM fungal hyphae called arbuscules reside. Development of the compartment occurs rapidly, coincident with intracellular penetration and rapid branching of the fungal hypha, and it requires much of the plant cell's secretory machinery to generate the periarbuscular membrane that delimits the compartment. Despite recent advances, our understanding of the development of the periarbuscular membrane and the transfer of molecules across the symbiotic interface is limited. Here, using electron microscopy and tomography, we reveal that the periarbuscular matrix contains two types of membrane-bound compartments. We propose that one of these arises as a consequence of biogenesis of the periarbuscular membrane and may facilitate movement of molecules between symbiotic partners. Additionally, we show that the arbuscule contains massive arrays of membrane tubules located between the protoplast and the cell wall. We speculate that these tubules may provide the absorptive capacity needed for nutrient assimilation and possibly water absorption to enable rapid hyphal expansion.
在丛枝菌根（AM）共生中，根皮层内的细胞会形成一个充满基质的质外体腔室，其中分化的 AM 真菌菌丝称为丛枝菌根驻留。腔室的发育非常迅速，与真菌菌丝的细胞内穿透和快速分枝同时发生，并且需要植物细胞的大部分分泌机制来产生限定腔室的丛枝菌根膜。尽管最近取得了一些进展，但我们对丛枝菌根膜的发育以及分子在共生界面上的转移的理解仍然有限。在这里，我们使用电子显微镜和断层扫描技术揭示了丛枝菌根基质包含两种类型的膜结合腔室。我们提出，其中一种腔室是丛枝菌根膜生物发生的结果，可能有助于共生体之间分子的移动。此外，我们还表明，丛枝内含有大量位于原生质体和细胞壁之间的膜小管。我们推测，这些小管可能为养分同化和可能的水分吸收提供所需的吸收能力，以实现快速菌丝扩展。
