Strigolactones Stimulate Arbuscular Mycorrhizal Fungi by Activating Mitochondria

Abstract

The association of arbuscular mycorrhizal (AM) fungi with plant roots is the oldest and ecologically most important symbiotic relationship between higher plants and microorganisms, yet the mechanism by which these fungi detect the presence of a plant host is poorly understood. Previous studies have shown that roots secrete a branching factor (BF) that strongly stimulates branching of hyphae during germination of the spores of AM fungi. In the BF of Lotus, a strigolactone was found to be the active molecule. Strigolactones are known as germination stimulants of the parasitic plants Striga and Orobanche. In this paper, we show that the BF of a monocotyledonous plant, Sorghum, also contains a strigolactone. Strigolactones strongly and rapidly stimulated cell proliferation of the AM fungus Gigaspora rosea at concentrations as low as 10 −13 M. This effect was not found with other sesquiterperne lactones known as germination stimulants of parasitic weeds. Within 1 h of treatment, the density of mitochondria in the fungal cells increased, and their shape and movement changed dramatically. Strigolactones stimulated spore germination of two other phylogenetically distant AM fungi, Glomus intraradices and Gl. claroideum. This was also associated with a rapid increase of mitochondrial density and respiration as shown with Gl. intraradices. We conclude that strigolactones are important rhizospheric plant signals involved in stimulating both the pre-symbiotic growth of AM fungi and the germination of parasitic plants.

Symbiosis with an endobacterium increases the fitness of a mycorrhizal fungus, raising its bioenergetic potential

“…In agreement with previous observations (Besserer et al, 2006), the 3-h treatment with GR24 increased the transcription of genes encoding NADH Dehydrogenase and COX 1 in both the lines (Supplementary Figure S8), with a significantly higher fold-change ratio in the B+ line for COX1 (Figure 7). By contrast, the results were less clear-cut when ROS-related genes were considered: only the transcript of glutathione peroxidase, which uses H 2 O 2 as a substrate, was strongly upregulated in the B+ spore, when compared with the cured line.…”

“…SLs stimulate mitochondrial activity in the germinating spores of the AMF Gigaspora rosea, which does not contain endobacteria (Besserer et al, 2006). Our analysis surprisingly reveals that the endobacterium and the SL treatment lead to a similar transcriptomic response under the tested conditions (7 days after germination), that is, upregulation of the genes encoding NADH dehydrogenase and Cytochrome oxidase I (COX 1) in the fungus.…”

“…The control of the intracellular concentration of calcium could be one of the key processes, first regulating the bioenergetic status of the fungus. Lastly, the comparison of the fungal transcriptome after treatment with a synthetic SL allowed us to reveal that both the endobacterium and SL produced a comparable response in the fungal mitochondria, possibly because the prokaryote and GR24 (Besserer et al, 2006) have a similar effect on the expression of respiratory genes. We suggest that SLs, which are usually considered as plant symbiotic signals, are first perceived by the AMF as foreign molecules (xenobiotics), activating a fast and transient [Ca2 + ] i increase, as well as elevated respiration, eventually leading to ROS production and detoxification.…”

Structural Insights into Maize Viviparous14, a Key Enzyme in the Biosynthesis of the Phytohormone Abscisic Acid

“…This involvement makes VP14 an attractive target for the development of novel chemical agents and genetic modifications to control ABA levels and improve plant productivity, performance, and architecture (Cutler and Krochko, 1999;Qin and Zeevaart, 1999) (Figure 1). Studies of the mutant vp14-2274 also implicate VP14 in the synthesis of strigolactones (Matusova et al, 2005), signaling molecules involved in shoot branching (Gomez-Roldan et al, 2008;Umehara et al, 2008), presymbiotic growth of arbuscular mycorrhizal fungi (Besserer et al, 2006), and parasitic weed germination (Hauck et al, 1992;Siame et al, 1993).…”

Role of mitochondria in the response of arbuscular mycorrhizal fungi to strigolactones

“…This enhancement of oxydative metabolism precedes active mitochondrial proliferation. 6,7 Taken together, these results suggested that mitochondrial activation is a key event required for switching the fungus to a pre-symbiotic stage, characterized by a more active nuclear proliferation, an upregulation of several genes and an activated cell proliferation (the so called branching response). 6 In order to clarify the role of mitochondria in the GR24 response, we carried out a series of pharmacological experiments where different steps of the oxidative phosphorylation were specifically inhibited.…”