Gastrodia elata, a fully mycoheterotrophic orchid without photosynthetic ability, only grows symbiotically with the fungus Armillaria. The mechanism of carbon distribution in this mycoheterotrophy is unknown. We detected high sucrose concentrations in all stages of Gastrodia tubers, suggesting sucrose may be the major sugar transported between fungus and orchid. Thick symplasm‐isolated wall interfaces in colonized and adjacent large cells implied involvement of sucrose importers. Two sucrose transporter (SUT)‐like genes, GeSUT4 and GeSUT3, were identified that were highly expressed in young Armillaria‐colonized tubers. Yeast complementation and isotope tracer experiments confirmed that GeSUT4 functioned as a high‐affinity sucrose‐specific proton‐dependent importer. Plasma‐membrane/tonoplast localization of GeSUT4‐GFP fusions and high RNA expression of GeSUT4 in symbiotic and large cells indicated that GeSUT4 likely functions in active sucrose transport for intercellular allocation and intracellular homeostasis. Transgenic Arabidopsis overexpressing GeSUT4 had larger leaves but were sensitive to excess sucrose and roots were colonized with fewer mutualistic Bacillus, supporting the role of GeSUT4 in regulating sugar allocation. This is not only the first documented carbon import system in a mycoheterotrophic interaction but also highlights the evolutionary importance of sucrose transporters for regulation of carbon flow in all types of plant‐microbe interactions.

中文翻译：

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GeSUT4在共生界面上介导蔗糖的导入，以实现异养天麻（兰科）的碳分配。

天麻，一种完全具有光合功能的异麦芽营养型兰花，仅与真菌蜜环菌共生。在这种真菌异养性中碳分布的机制尚不清楚。我们在天麻块茎的所有阶段都检测到了高浓度的蔗糖，表明蔗糖可能是真菌和兰花之间运输的主要糖分。在定植的和邻近的大细胞中厚厚的隔离物隔离的壁界面暗示了蔗糖进口商的参与。鉴定出两个类似蔗糖转运蛋白（SUT）的基因GeSUT4和GeSUT3，它们在年轻的蜜环菌定殖块茎中高表达。酵母互补和同位素示踪实验证实Ge SUT4充当了高亲和力的特定于蔗糖的质子依赖进口商。Ge SUT4-GFP融合蛋白的质膜/液泡定位和GeSUT4在共生和大细胞中的高RNA表达表明Ge SUT4可能在活性蔗糖转运中发挥功能，以实现细胞间分配和细胞内稳态。过表达GeSUT4的转基因拟南芥具有较大的叶片，但对过量的蔗糖敏感，根部的互生芽孢杆菌较少，支持了Ge的作用。SUT4在调节糖分配中。这不仅是真菌异养相互作用中第一个有记录的碳导入系统，而且突出了蔗糖转运蛋白在调节所有类型的植物-微生物相互作用中碳流量方面的进化重要性。