Huisman Rik, Hontelez Jan, Bisseling Ton, Limpens Erik
Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University & Research, Wageningen, Netherlands.
Front Plant Sci. 2020 Apr 3;11:354. doi: 10.3389/fpls.2020.00354. eCollection 2020.
How cells control the proper delivery of vesicles and their associated cargo to specific plasma membrane (PM) domains upon internal or external cues is a major question in plant cell biology. A widely held hypothesis is that expansion of plant exocytotic machinery components, such as SNARE proteins, has led to a diversification of exocytotic membrane trafficking pathways to function in specific biological processes. A key biological process that involves the creation of a specialized PM domain is the formation of a host-microbe interface (the peri-arbuscular membrane) in the symbiosis with arbuscular mycorrhizal fungi. We have previously shown that the ability to intracellularly host AM fungi correlates with the evolutionary expansion of both v- (VAMP721d/e) and t-SNARE (SYP132α) proteins, that are essential for arbuscule formation in . Here we studied to what extent the symbiotic SNAREs are different from their non-symbiotic family members and whether symbiotic SNAREs define a distinct symbiotic membrane trafficking pathway. We show that all tested SYP1 family proteins, and most of the non-symbiotic VAMP72 members, are able to complement the defect in arbuscule formation upon knock-down/-out of their symbiotic counterparts when expressed at sufficient levels. This functional redundancy is in line with the ability of all tested v- and t-SNARE combinations to form SNARE complexes. Interestingly, the symbiotic t-SNARE SYP132α appeared to occur less in complex with v-SNAREs compared to the non-symbiotic syntaxins in arbuscule-containing cells. This correlated with a preferential localization of SYP132α to functional branches of partially collapsing arbuscules, while non-symbiotic syntaxins accumulate at the degrading parts. Overexpression of VAMP721e caused a shift in SYP132α localization toward the degrading parts, suggesting an influence on its endocytic turn-over. These data indicate that the symbiotic SNAREs do not selectively interact to define a symbiotic vesicle trafficking pathway, but that symbiotic SNARE complexes are more rapidly disassembled resulting in a preferential localization of SYP132α at functional arbuscule branches.
细胞如何根据内部或外部信号将囊泡及其相关货物正确递送至特定的质膜（PM）结构域，这是植物细胞生物学中的一个主要问题。一个被广泛接受的假说是，植物胞吐机制成分（如SNARE蛋白）的扩展导致了胞吐膜运输途径的多样化，以在特定的生物学过程中发挥作用。一个涉及形成特殊质膜结构域的关键生物学过程是在与丛枝菌根真菌共生过程中形成宿主 - 微生物界面（丛枝周膜）。我们之前已经表明，细胞内宿主丛枝菌根真菌的能力与v - （VAMP721d/e）和t - SNARE（SYP132α）蛋白的进化扩展相关，这些蛋白对于丛枝的形成至关重要。在这里，我们研究了共生SNARE与其非共生家族成员的差异程度，以及共生SNARE是否定义了一条独特的共生膜运输途径。我们表明，所有测试的SYP1家族蛋白以及大多数非共生VAMP72成员，当以足够的水平表达时，能够在其共生对应物被敲低/敲除后补充丛枝形成中的缺陷。这种功能冗余与所有测试的v - 和t - SNARE组合形成SNARE复合体的能力一致。有趣的是，与含丛枝细胞中的非共生 syntaxins相比，共生t - SNARE SYP132α与v - SNAREs形成复合体的情况似乎较少。这与SYP132α优先定位于部分塌陷丛枝的功能分支相关，而非共生syntaxins则聚集在降解部分。VAMP721e的过表达导致SYP132α的定位向降解部分转移，表明对其胞吞周转有影响。这些数据表明，共生SNARE并非选择性相互作用以定义一条共生囊泡运输途径，而是共生SNARE复合体更快地解体，导致SYP132α优先定位于功能性丛枝分支处。
