Establishment of arbuscular mycorrhiza (AM) relies on a plant signaling pathway that can be activated by fungal chitinic signals such as short chain chitooligosaccharides (CO) and lipo-chitooligosaccharides (LCOs). The tomato LysM receptor-like kinase (LysM RLK) SlLYK10 has high affinity for LCOs and is involved in root colonization by arbuscular mycorrhizal fungi (AMF), however its role in LCO responses has not yet been studied. Here, we show that SlLYK10 proteins produced by the Sllyk10-1 and Sllyk10-2 mutant alleles, which both cause decreases in AMF colonization, and carry mutations in LysM1 and 2 respectively, have similar LCO binding affinities compared to the WT SlLYK10. However, the mutant forms were no longer able to induce cell death in Nicotiana benthamiana when co-expressed with MtLYK3, a Medicago truncatula LCO co-receptor, while they physically interacted with MtLYK3 in co-purification experiments. This suggests that the LysM mutations affect the ability of SlLYK10 to trigger signaling through a potential co-receptor rather than its ability to bind LCOs. Interestingly, tomato lines that contain a calcium (Ca2+) concentration reporter (Genetically Encoded Ca2+ indicators, GECO), showed Ca2+ spiking in response to LCO applications, but this occurred only in inner cell layers of the roots, while short chain COs also induced Ca2+ spiking in the epidermis. Moreover, LCO-induced Ca2+spiking was decreased in Sllyk10-1*GECO plants, suggesting that the decrease in AMF colonization in Sllyk10-1 is due to abnormal LCO signaling.

中文翻译：

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LysM 受体样激酶 SlLYK10 控制番茄根内细胞层中的脂壳寡糖信号传导

丛枝菌根 (AM) 的建立依赖于植物信号通路，该通路可被真菌几丁质信号激活，例如短链壳寡糖 (CO) 和脂壳寡糖 (LCO)。番茄 LysM 受体样激酶 (LysM RLK) SlLYK10 对 LCO 具有高亲和力，并参与丛枝菌根真菌 (AMF) 的根定植，但其在 LCO 反应中的作用尚未研究。在这里，我们表明，由 Slyk10-1 和 Sllyk10-2 突变等位基因产生的 SlLYK10 蛋白与 WT SlLYK10 相比，具有相似的 LCO 结合亲和力，这两种等位基因都会导致 AMF 定植减少，并分别携带 LysM1 和 2 突变。然而，当突变体与蒺藜苜蓿 LCO 共受体 MtLYK3 共表达时，它们不再能够诱导本塞姆氏烟草的细胞死亡，同时它们在共纯化实验中与 MtLYK3 发生物理相互作用。这表明 LysM 突变影响 SlLYK10 通过潜在共受体触发信号传导的能力，而不是影响其结合 LCO 的能力。有趣的是，含有钙 (Ca2+) 浓度报告器（基因编码 Ca2+ 指示剂，GECO）的番茄品系在 LCO 应用后显示出 Ca2+ 峰值，但这仅发生在根部的内细胞层，而短链 CO 也诱导 Ca2+刺入表皮。此外，在 Sllyk10-1*GECO 植物中，LCO 诱导的 Ca2+ 尖峰减少，表明 Sllyk10-1 中 AMF 定植的减少是由于异常的 LCO 信号传导所致。