Arbuscular mycorrhizal symbiosis is a mutualistic interaction between most land plants and fungi of the glomeromycotina subphylum. The initiation, development and regulation of this symbiosis involve numerous signalling events between and within the symbiotic partners. Among other signals, phytohormones are known to play important roles at various stages of the interaction. During presymbiotic steps, plant roots exude strigolactones which stimulate the fungus, and favour the initiation of symbiosis. At later stages, different plant hormone classes can act as positive or negative regulators of the interaction. Although the fungus is known to reciprocally emit regulatory signals, its potential contribution to the phytohormonal pool has received little attention, and has so far only been addressed by indirect assays. In this study, using mass spectrometry, we analyzed phytohormones released into the medium by germinated spores of the arbuscular mycorrhizal fungus Rhizophagus irregularis. We detected the presence of a cytokinin (isopentenyl-adenosine) and an auxin (indole-acetic acid). In addition, we identified a gibberellin (gibberellic acid 4) in spore extracts. We also used gas chromatography to show that R. irregularis produces ethylene from methionine and the α-keto γ-methylthiobutyric acid pathway. These results highlight the possibility for AM fungi to use phytohormones to interact with their host plants, or to regulate their own development.

中文翻译：

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丛枝菌根真菌不规则根瘤菌产生植物激素

丛枝菌根共生是大多数陆地植物与次小球藻真菌之间的相互影响。这种共生的启动，发展和调节涉及共生伴侣之间和之内的许多信号传导事件。在其他信号中，已知植物激素在相互作用的各个阶段起重要作用。在共生前的步骤中，植物根系散发出可刺激真菌并促进共生的松香内酯。在以后的阶段，不同的植物激素类别可以充当相互作用的正或负调节剂。尽管已知该真菌会相互发出调节信号，但是其对植物激素库的潜在贡献却鲜有关注，并且迄今为止仅通过间接测定法得以解决。在这个研究中，使用质谱，我们分析了丛枝菌根真菌不规则根瘤菌的发芽孢子释放到培养基中的植物激素。我们检测到细胞分裂素（异戊烯基腺苷）和生长素（吲哚乙酸）的存在。此外，我们在孢子提取物中鉴定了赤霉素（赤霉素4）。我们还使用气相色谱法显示不规则红球菌从蛋氨酸和α-酮γ-甲基硫代丁酸途径生产乙烯。这些结果突显了AM真菌使用植物激素与其寄主植物相互作用或调节其自身发育的可能性。我们检测到细胞分裂素（异戊烯基腺苷）和生长素（吲哚乙酸）的存在。此外，我们在孢子提取物中鉴定了赤霉素（赤霉素4）。我们还使用气相色谱法显示不规则红球菌从蛋氨酸和α-酮基γ-甲基硫代丁酸途径生产乙烯。这些结果突显了AM真菌使用植物激素与其宿主植物相互作用或调节自身发育的可能性。我们检测到细胞分裂素（异戊烯基-腺苷）和生长素（吲哚-乙酸）的存在。此外，我们在孢子提取物中鉴定了赤霉素（赤霉素4）。我们还使用气相色谱法显示不规则红球菌从蛋氨酸和α-酮γ-甲基硫代丁酸途径生产乙烯。这些结果突显了AM真菌使用植物激素与其宿主植物相互作用或调节自身发育的可能性。