Exogenous myristate promotes the colonization of arbuscular mycorrhizal fungi in tomato

Abstract

Arbuscular mycorrhizal fungi (AMF) can establish symbiotic associations with the roots of most terrestrial plants, thereby improving the tolerance of the host plants to biotic and abiotic stresses. Although AMF cannot synthesize lipids de novo, they can obtain lipids from the root cells for their growth and development. A recent study reveals that AMF can directly take up myristate (C14:0 lipid) from the environment and produce a large amount of hyphae in asymbiotic status; however, the effect of environmental lipids on AM symbiosis is still unclear. In this study, we inoculated tomato (Solanum lycopersicum) with AMF in an in vitro dual culture system and a sand culture system, and then applied exogenous myristate to the substrate, in order to explore the effect of exogenous lipids on the mycorrhizal colonization of AMF. We investigated the hyphae growth, development, and colonization of AMF, and examined the gene expression involved in phosphate transport, lipid biosynthesis, and transport. Results indicate that exogenous lipids significantly stimulated the growth and branching of hyphae, and significantly increased the number of hyphopodia and mycorrhizal colonization of AMF, with arbuscular abundance and intraradical spores or vesicles being the most promoted. In contrast, exogenous myristate decreased the growth range and host tropism of the germ tubes, and largely inhibited the exchange of nutrition between symbionts. As a result, exogenous myristate did not affect the plant growth. This study suggests that lipids promote mycorrhizal colonization by enhancing the growth and development of AMF hyphae and increasing their contact opportunities with plant roots. To the best of our knowledge, this is the first report that shows that lipids promote the colonization of AMF. Our study highlights the importance of better understanding the roles of environmental lipids in the establishment and maintenance of AM symbiosis and, thus, in agricultural production.

Tap into non-symbiotic carbon? Exogenous myristate fuels the growth of symbiotic arbuscular mycorrhizal fungi but disrupts their carbon‒phosphorus exchange with host plants

“…Intriguingly, exogenous myristate caused a loss of directional growth in extraradical hyphae towards the roots (tropism) in our study (Fig. 1) and in others’ research (Liu et al ., 2023), suggesting an interruption in the normal signal communication in AM. Notably, the signaling role of myristate has also been found in several soil-borne bacteria (Fernández-Piñar et al ., 2012; Liu et al ., 2024), implying its universal role in regulating the soil microbiome.…”

“…However, the extent to which the physiological and ecological responses of AMF to external myristate during the asymbiotic phase mirror those in symbiotic growth, the typical state of AMF in nature, remains unclear. A recent investigation reported that although exogenous myristate does not affect the extraradical biomass of symbiotic AMF, it enhances AMF colonization by stimulating the growth and development of extraradical hyphae (Liu et al ., 2023). To date, the effects of exogenous fatty acid on AM symbiosis and their underlying mechanisms are still largely unexplored.…”