Diffusible Signal from Arbuscular Mycorrhizal Fungi Elicits a Transient Cytosolic Calcium Elevation in Host Plant Cells

• Published in: Plant physiology (Bethesda) 2007-06, Vol.144 (2), p.673-681
• Main Authors: Navazio, Lorella, Moscatiello, Roberto, Genre, Andrea, Novero, Mara, Baldan, Barbara, Bonfante, Paola, Mariani, Paola
• Format: Article
• Language: English
• Subjects: Aequorin - metabolism; Arabidopsis - metabolism; Arabidopsis thaliana; Biological and medical sciences; Calcium - metabolism; Calcium Signaling - physiology; Cell culture techniques; Cell physiology; Cell walls; Cells, Cultured; Culture Media - metabolism; Cultured cells; Cytosol - metabolism; Focus Issue on Legume Biology; Fundamental and applied biological sciences. Psychology; Fungal spores; Gene Expression Regulation, Plant; Gigaspora margarita; Glomus; Glycine max; Glycine max - genetics; Glycine max - metabolism; Glycine max - microbiology; Hot Temperature; Medicago truncatula; Medicago truncatula - genetics; Molecular and cellular biology; Molecules; Mycorrhizae - metabolism; Plant cells; Plants; Signal transduction; Soybeans; Spore germination; Spores, Fungal - growth & development; Spores, Fungal - metabolism; Surface-Active Agents - metabolism; Symbiosis; Symbiosis - physiology; Up-Regulation
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.106.086959

The implication of calcium as intracellular messenger in the arbuscular mycorrhizal (AM) symbiosis has not yet been directly demonstrated, although often envisaged. We used soybean (Glycine max) cell cultures stably expressing the bioluminescent Ca²⁺ indicator aequorin to detect intracellular Ca²⁺ changes in response to the culture medium of spores of Gigaspora margarita germinating in the absence of the plant partner. Rapid and transient elevations in cytosolic free Ca²⁺ were recorded, indicating that diffusible molecules released by the mycorrhizal fungus are perceived by host plant cells through a Ca²⁺-mediated signaling. Similar responses were also triggered by two Glomus isolates. The fungal molecules active in generating the Ca²⁺ transient were constitutively released in the medium, and the induced Ca²⁺ signature was not modified by the coculture of germinating spores with plant cells. Even ungerminated spores were able to generate the signaling molecules, as proven when the germination was blocked by a low temperature. The fungal molecules were found to be stable to heat treatment, of small molecular mass (