ARS | Publication request: The effects of hydroxy fatty acids on the hyphal branching of germinated spores of AM fungi

Submitted to: Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 26, 2011
Publication Date: February 26, 2011
Citation: Nagahashi, G., Douds, D.D. 2011. The effects of hydroxy fatty acids on the hyphal branching of germinated spores of AM fungi. Fungal Biology. 115:351-358.

Interpretive Summary: Arbuscular mycorrhizal [AM] fungi are beneficial soil fungi that have been shown to increase the nutrient uptake, disease resistance, and drought resistance of crop plants. Utilization of these fungi, potentially important in sustainable agriculture, is hampered by our inability to grow them by themselves in the laboratory. Something supplied by the plant root enables AM fungi to grow and complete their life cycles. Understanding the communication between roots and AM fungi is essential to eventually growing these fungi for large scale use in agriculture. One aspect of this communication is a chemical signal released from the root which produces a change in growth pattern in the fungus. This helps it find the root. We have isolated and identified three of these signal molecules via sophisticated analytical techniques and verified that they produce the change in growth pattern in an AM fungus. These results now allow us to test whether these chemicals will be helpful in allowing AM fungi to complete their life cycles in the absence of plant roots and enable inoculum production for large scale use in agriculture.

Technical Abstract: Abietic acid (Aba), dehydroabietic acid (DAba), and 2-hydroxytetradecanoic acid (2-HTDA) were identified by Fourier Transform Ion Cyclotron Mass Spectroscopy and found to be elevated in the exudate of Ri T-DNA transformed carrot roots that were grown in the absence relative to the presence of phosphorus in liquid culture. Five µM DAba stimulated a significant number of lateral branches on the primary germ tube of Gigaspora gigantea and an unidentified Gigaspora(sp). The stimulation was more pronounced with G. gigantea and the number of lateral branches increased 5-fold over the control. However, 5 uM Aba had no affect on G. gigantea but doubled the growth and branches of Gigaspora (sp). Although some of the quantified measurements of hyphal growth parameters were similar for both species, there were considerable differences in hyphal growth morphology induced by these compounds. DAba and Aba both stimulated the elongation growth of the main germ tube of Glomus intraradices but they also inhibited the lateral branch formation. Two-HTDA at 10 nM did not affect the growth of germinated spores of G. intraradices, however, it stimulated all of the hyphal growth parameters measured for G. gigantea and to a lesser extent, those of Gigaspora (sp). These results will be discussed in terms of hyphal growth elongators and hyphal branching factors (BFs) and their likely synergistic effects.