Russo Giulia, Carotenuto Gennaro, Fiorilli Valentina, Volpe Veronica, Faccio Antonella, Bonfante Paola, Chabaud Mireille, Chiapello Marco, Van Damme Daniel, Genre Andrea
Department of Agricultural, Forest and Food Sciences, University of Torino, Torino, Italy.
Department of Life Sciences and Systems Biology, University of Torino, Torino, Italy.
Front Plant Sci. 2019 Dec 20;10:1628. doi: 10.3389/fpls.2019.01628. eCollection 2019.
Arbuscular mycorrhizal (AM) symbiosis between soil fungi and the majority of plants is based on a mutualistic exchange of organic and inorganic nutrients. This takes place inside root cortical cells that harbor an arbuscule: a highly branched intracellular fungal hypha enveloped by an extension of the host cell membrane-the perifungal membrane-which outlines a specialized symbiotic interface compartment. The perifungal membrane develops around each intracellular hypha as the symbiotic fungus proceeds across the root tissues; its biogenesis is the result of an extensive exocytic process and shows a few similarities with cell plate insertion which occurs at the end of somatic cytokinesis. We here analyzed the subcellular localization of a GFP fusion with TPLATE, a subunit of the endocytic TPLATE complex (TPC), a central actor in plant clathrin-mediated endocytosis with a role in cell plate anchoring with the parental plasma membrane. Our observations demonstrate that and root organ cultures expressing a 35S::TPLATE-GFP construct accumulate strong fluorescent green signal at sites of symbiotic interface construction, along recently formed perifungal membranes and at sites of cell-to-cell hyphal passage between adjacent cortical cells, where the perifungal membrane fuses with the plasmalemma. Our results strongly suggest that TPC-mediated endocytic processes are active during perifungal membrane interface biogenesis-alongside exocytic transport. This novel conclusion, which might be correlated to the accumulation of late endosomes in the vicinity of the developing interface, hints at the involvement of TPC-dependent membrane remodeling during the intracellular accommodation of AM fungi.
土壤真菌与大多数植物之间的丛枝菌根（AM）共生关系基于有机和无机养分的互利交换。这种交换发生在含有丛枝的根皮层细胞内：丛枝是一种高度分支的细胞内真菌菌丝，被宿主细胞膜的延伸部分——真菌周膜——所包裹，真菌周膜勾勒出一个特殊的共生界面隔室。随着共生真菌穿过根组织，真菌周膜在每个细胞内菌丝周围形成；其生物发生是广泛胞吐过程的结果，与体细胞胞质分裂末期发生的细胞板插入有一些相似之处。我们在此分析了绿色荧光蛋白（GFP）与TPLATE的融合蛋白的亚细胞定位，TPLATE是内吞TPLATE复合体（TPC）的一个亚基，TPC是植物网格蛋白介导的内吞作用中的核心参与者，在细胞板与亲本质膜的锚定中起作用。我们的观察结果表明，表达35S::TPLATE-GFP构建体的根器官培养物在共生界面构建位点、沿着新形成的真菌周膜以及相邻皮层细胞之间的细胞间菌丝通道位点（真菌周膜与质膜融合的地方）积累强烈的绿色荧光信号。我们的结果强烈表明，在真菌周膜界面生物发生过程中，TPC介导的内吞过程与胞吐运输同时活跃。这一新结论可能与发育中的界面附近晚期内体的积累有关，暗示了在丛枝菌根真菌的细胞内容纳过程中TPC依赖性膜重塑的参与。
