Laboratoire de Recherche en Sciences Végétales, CNRS, Université de Toulouse, UPS, 24 chemin de Borde Rouge, Auzeville, 31320, Castanet-Tolosan, France.
CNRS, Institut de Chimie des Substances Naturelles, Université Paris-Saclay, UPR 2301, 91198, Gif-sur-Yvette, France.
Mycorrhiza. 2020 Jul;30(4):491-501. doi: 10.1007/s00572-020-00965-9. Epub 2020 Jun 6.
The arbuscular mycorrhizal symbiosis is a very common association between plant roots and soil fungi, which greatly contributes to plant nutrition. Root-exuded compounds known as strigolactones act as symbiotic signals stimulating the fungus prior to root colonization. Strigolactones also play an endogenous role in planta as phytohormones and contribute to the regulation of various developmental traits. Structure-activity relationship studies have revealed both similarities and differences between the structural features required for bioactivity in plants and arbuscular mycorrhizal fungi. In the latter case, bioassays usually measured a stimulation of hyphal branching on isolated fungi of the Gigaspora genus, grown in vitro. Here, we extended these investigations with a bioassay that evaluates the bioactivity of strigolactone analogs in a symbiotic situation and the use of the model mycorrhizal fungus Rhizophagus irregularis. Some general structural requirements for bioactivity reported previously for Gigaspora were confirmed. We also tested additional strigolactone analogs bearing modifications on the conserved methylbutenolide ring, a key element of strigolactone perception by plants. A strigolactone analog with an unmethylated butenolide ring could enhance the ability of R. irregularis to colonize host roots. Surprisingly, when applied to the isolated fungus in vitro, this compound stimulated germ tube elongation but inhibited hyphal branching. Therefore, this compound was able to act on the fungal and/or plant partner to facilitate initiation of the arbuscular mycorrhizal symbiosis, independently from hyphal branching and possibly from the strigolactone pathway.
丛枝菌根共生是植物根系与土壤真菌之间非常常见的共生关系，它极大地促进了植物的营养吸收。植物根系分泌的化合物被称为独脚金内酯，作为共生信号，在真菌定殖前刺激真菌。独脚金内酯在植物体内也发挥着内源激素的作用，参与调控各种发育特征。结构-活性关系研究揭示了植物和丛枝菌根真菌中生物活性所需结构特征的相似性和差异性。在后一种情况下，生物测定通常测量在体外培养的孤立巨型孢属真菌上的菌丝分枝刺激。在这里，我们通过生物测定扩展了这些研究，该测定评估了独脚金内酯类似物在共生情况下的生物活性，以及模式菌根真菌粗糙脉孢菌的应用。我们证实了以前针对巨型孢属报道的生物活性的一些一般结构要求。我们还测试了其他具有保守的甲基丁烯内酯环修饰的独脚金内酯类似物，该环是植物独脚金内酯感知的关键元素。一个具有未甲基化丁烯内酯环的独脚金内酯类似物可以增强粗糙脉孢菌定殖宿主根系的能力。令人惊讶的是，当将该化合物应用于体外的分离真菌时，它刺激了芽管伸长，但抑制了菌丝分枝。因此，该化合物能够通过作用于真菌和/或植物伙伴来促进丛枝菌根共生的起始，而不依赖于菌丝分枝，可能也不依赖于独脚金内酯途径。
