The intracellular colonization of plant roots by the beneficial fungal endophyte Serendipita indica follows a biphasic strategy, including a host cell death phase that enables successful colonization of Arabidopsis thaliana roots. How host cell death is initiated and controlled is largely unknown. Here, we show that two fungal enzymes, the ecto-5′-nucleotidase SiE5NT and the nuclease SiNucA, act synergistically in the apoplast at the onset of cell death to produce deoxyadenosine (dAdo). The uptake of extracellular dAdo but not the structurally related adenosine activates cell death via the equilibrative nucleoside transporter ENT3. We identified a previously uncharacterized Toll-like interleukin 1 receptor (TIR)-nucleotide-binding leucine-rich repeat receptor (NLR) protein, ISI (induced by S. indica), as an intracellular factor that affects host cell death, fungal colonization, and growth promotion. Our data show that the combined activity of two fungal apoplastic enzymes promotes the production of a metabolite that engages TIR-NLR-modulated pathways to induce plant cell death, providing a link to immunometabolism in plants.

中文翻译：

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真菌内生真菌产生的核苷信号调节宿主细胞死亡并促进根定植


有益真菌内生菌 Serendipita indica 对植物根的细胞内定植遵循双相策略，包括宿主细胞死亡阶段，使拟南芥根能够成功定植。宿主细胞死亡是如何发生和控制的在很大程度上是未知的。在这里，我们表明两种真菌酶，胞外-5′-核苷酸酶 SiE5NT 和核酸酶 SiNucA，在细胞死亡开始时在质外质体中协同作用以产生脱氧腺苷 （dAdo）。细胞外 dAdo 的摄取而不是结构相关的腺苷通过平衡核苷转运蛋白 ENT3 激活细胞死亡。我们确定了一种以前未表征的 Toll 样白细胞介素 1 受体 （TIR） 核苷酸结合富含亮氨酸的重复受体 （NLR） 蛋白 ISI（由籼稻链球菌 诱导），作为影响宿主细胞死亡、真菌定植和生长促进的细胞内因子。我们的数据表明，两种真菌质外体酶的联合活性促进了代谢物的产生，该代谢物参与 TIR-NLR 调节途径以诱导植物细胞死亡，从而与植物中的免疫代谢有关。