Arbuscular mycorrhizal fungi (AMF) rely on their host plants to provide them with fatty acids (FA), but the precise form(s) in which they are supplied is still unclear. Here we show that ectopic expression of the transcription factor REQUIRED FOR ARBUSCULAR MYCORRHIZATION 1 (RAM1) can drive secretion of 2-monoacylglycerols (2MGs) from Medicago truncatula roots and that their main FA moiety is palmitic acid, although myristic acid and stearic acid were also detected. RAM1-dependend 2MG secretion requires the acyl-acyl carrier protein thioesterase FATM, the glycerol-3-phosphate (G3P) acyltransferase RAM2 and the ATP binding cassette transporter STR. Furthermore, 14C glycerol labelling experiments using mycorrhizal M. truncatula roots that are deficient in glycerol kinase, FAD-dependent G3P dehydrogenase and the G3P acyltransferase RAM2 suggest that most of the glyceryl moieties in Rhizophagus irregularis storage lipids are provided by their host plant through the 2MG pathway. Taken together, our data support the hypothesis that the plant exports 2MGs across the peri-arbuscular membrane in mycorrhizal roots and that the AMF receive and utilise both the FA and glyceryl moieties to make their storage lipids.

中文翻译：

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植物输出2-monopalmitin并向丛枝菌根真菌供应脂肪酰基和甘油基部分

丛枝菌根真菌（AMF）依靠其寄主植物向其提供脂肪酸（FA），但提供它们的确切形式仍不清楚。在这里，我们显示异位表达所需的丛枝菌丝化1（RAM1）可以驱动2-丁二酰甘油（2MGs）从Medi藜根中分泌，并且它们的主要FA部分是棕榈酸，尽管肉豆蔻酸和硬脂酸也是检测到。依赖RAM1的2MG分泌需要酰基-酰基载体蛋白硫酯酶FATM，3-磷酸甘油（G3P）酰基转移酶RAM2和ATP结合盒转运蛋白STR。此外，使用缺乏甘油激酶的菌根M根的14C甘油标记实验，FAD依赖的G3P脱氢酶和G3P酰基转移酶RAM2表明，不规则根瘤菌贮藏脂质中的大多数甘油部分是由其宿主植物通过2MG途径提供的。综上所述，我们的数据支持以下假设：植物在菌根根部穿过丛周膜输出2MG，而AMF接收并利用FA和甘油基来制造其脂质。