Phytohormone production by the arbuscular mycorrhizal fungusRhizophagus irregularis

Abstract

20 * Correspondence to: puech@lrsv.ups-tlse.fr, +33 (0)5 34 32 38 31 (VPP) and frei-dit-21 frey@lrsv.ups-tlse.fr (NFdF), +33 (0)5 34 32 38 60 22 23 Text word count: 5465 24 Number of figure: 3 25 -Fig. 1 Detection by LC-MS of iPR and IAA exuded by R. irregularis spores (colour print) 26 -Fig. 2 GA 4 detection in multiple reactions monitoring (MRM) mode (colour print) HIGLIGHT 31 In this work, we provide for the first time direct experimental evidence, by mass 32 spectrometry and gas chromatography analyses, that the model AM fungus Rhizophagus 33 irregularis produces four different phytohormones. 34 ABSTRACT 35 Arbuscular Mycorrhizal (AM) symbiosis is a mutualistic interaction between most land 36 plants and fungi of the glomeromycotina subphylum. The initiation, development and regulation 37 of this symbiosis involve numerous signalling events between and within the symbiotic partners. 38 Among other signals, phytohormones are known to play important roles at various stages of the 39 interaction. During presymbiotic steps, plant roots exude strigolactones which stimulate the 40 fungus, and favour the initiation of symbiosis. At later stages, different plant hormone classes 41 can act as positive or negative regulators of the interaction. Although the fungus is known to 42 reciprocally emit regulatory signals, its potential contribution to the phytohormonal pool has 43 received little attention, and has so far only been addressed by indirect assays. In this study, 44 using mass spectrometry, we detected the presence of a cytokinin (isopentenyl-adenosine), an 45 auxin (indole-acetic acid), and a gibberellin (gibberellic acid 4), in germinating spores or 46 exudates of Rhizophagus irregularis. We also used gas chromatography to show that R. 47 irregularis produces ethylene from methionine and the α -keto γ -methylthiobutyric acid (KMBA) 48 pathway. These results highlight the possibility for AM fungi to use phytohormones to interact 49 with their host plants, or to regulate their own development. 50 51 KEYWORDS: 52 Arbuscular mycorrhizal fungi Abscisic acid (ABA) 63 Aminocyclopropane-carboxylate (ACC) 64Aminocyclopropane-carboxylate oxidase (ACO) 65 93 Arbuscular Mycorrhizal (AM) symbiosis is a 460 million-year-old interaction (Redecker, 94 2000) between glomeromycotina fungi and over 70% of land plants (Brundrett and Tedersoo, 95 2018). In angiosperms, AM fungi colonize the inner root cortex of their host to develop 96 intracellular ramified structures called arbuscules. These arbuscules are the main site for nutrient 97 exchange between the plant and the fungus. AM fungi provide their host plant with water and 98 minerals, in return for photosynthetic carbon (mainly sugars and lipids) (Smith and Read, 2008; 99

Responses of Arbuscular Mycorrhizal Symbiosis to Abiotic Stress: A Lipid-Centric Perspective

“…Remarkably, the content of ABA in AM fungi is more than one order of magnitude higher than that in plant roots (Esch et al, 1994). Pons et al (2020) provided direct evidence that AM fungi can synthesize cytokinins, auxin, gibberellins, and ethylene but not ABA, which indicates that ABA in AM fungi is derived from plants. Therefore, functional genes responsible for ABA biosynthesis in AM fungi or transporters responsible for transporting ABA from the roots to AM fungi remain unexplored.…”

Volatile organic compounds shape belowground plant–fungi interactions

“…The SA is dispersed over several centimeters and is transformed into its volatile derivatives, which then alter the structure of microbial communities (Dehimeche et al, 2021;Kong et al, 2021). Notably, Pons et al (2020) found that phytohormones including cytokinin (isopentenyl adenosine), an auxin (indole-acetic acid), gibberellin (gibberellin A4), and ethylene are also produced by the AM fungus Rhizophagus irregularis. Similarly, the EM fungus Tricholoma vaccinum emits ethylene and excretes ABA, SA, jasmonates, and indole-3-acetid acid (Abdulsalam et al, 2021).…”