Abstract
A simulation of the environment inhabited by arbuscular mycorrhizal (AM) fungi could provide clues as to how to cultivate these obligate biotrophs axenically. Host intraradical and rhizospheric environments, root extracts and exudates in particular, would be crucial for AM fungi to complete their life cycles. In this study, we analyzed and compared the effects of root exudates (RE) and root extracts (RET) of white clover (Trifolium repens) on the asymbiotic growth of the AM fungus Funneliformis mosseae in vitro, and furtherly analyzed the chemical components of different RET with the LC-MS/MS technique in order to establish an asymbiotic cultivation system for this important and hardly domesticated AM fungus. RET is superior to RE in stimulating spore germination, hyphal elongation and branching, and secondary spore formation (p < 0.05). RET-induced effects were dependent on phosphate supplement levels, and the RET obtained following the treatment with low levels of phosphorus significantly promoted hyphal growth and sporulation (p < 0.05). A few newly formed secondary spores showed limited colonization of white clover roots. The low phosphorus-induced effects could be ascribed to the metabolic adjustment (mainly lipids and organic acids) of white clover roots under low phosphate conditions. Our findings demonstrate that the low phosphate-induced RET boosts the asymbiotic growth of AM fungus, and thus offers an alternative way to fulfill the life cycle of AM fungi asymbiotically.
Highlights
Arbuscular mycorrhizal (AM) fungi are asexual obligate biotrophic symbionts that are dependent on carbon supplied by the roots of their host and are incapable of completing their life cycles asymbiotically [1]
The observation of branch-absorbing structures (BAS) in this study indicates that the growth pattern of F. mosseae when supplemented with root extracts (RET) from the low phosphate treatment mimicked the growth pattern of AM fungi at the symbiotic stage
Our results demonstrate the promotion effects of RET on F. mosseae asymbiotic growth and infection-competent SS production, opening an alternative route for propagating AM fungi in future
Summary
Arbuscular mycorrhizal (AM) fungi are asexual obligate biotrophic symbionts that are dependent on carbon supplied by the roots of their host and are incapable of completing their life cycles asymbiotically [1]. A wide range of compounds (e.g., flavonoids, polyamines, cutin monomers, plant hormones, etc.) have been reported to promote AM fungal presymbiotic hyphal growth, branching and colonization efficiency [2,3,4,5,6] Among these compounds, the branching factor, strigolactones (SLs), received the most concern, and they have been shown to greatly promote the hyphal ramification of AM fungi to initiate the establishment of AM symbiosis [7,8]. The branching factor, strigolactones (SLs), received the most concern, and they have been shown to greatly promote the hyphal ramification of AM fungi to initiate the establishment of AM symbiosis [7,8] These compounds could promote the asymbiotic growth of AM fungi, there is no evidence that these stimulators could stimulate AM fungal sporulation and help fulfill their life cycles in vitro. Rather than a core compound determining the completion of AM fungi life cycles, it seems more likely that blends of compounds are needed for AM fungi to survive asymbiotically [6]
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