bFungus-derived indole-3-acetic acid (IAA), which is involved in development of ectomycorrhiza, affects both partners, i.e., the tree and the fungus. The biosynthesis pathway, excretion from fungal hyphae, the induction of branching in fungal cultures, and enhanced Hartig net formation in mycorrhiza were shown. Gene expression studies, incorporation of labeled compounds into IAA, heterologous expression of a transporter, and bioinformatics were applied to study the effect of IAA on fungal morphogenesis and on ectomycorrhiza. Tricholoma vaccinum produces IAA from tryptophan via indole-3-pyruvate, with the last step of this biosynthetic pathway being catalyzed by an aldehyde dehydrogenase. The gene ald1 was found to be highly expressed in ectomycorrhiza and induced by indole-3-acetaldehyde. The export of IAA from fungal cells is supported by the multidrug and toxic extrusion (MATE) transporter Mte1 found in T. vaccinum. The addition of IAA and its precursors induced elongated cells and hyphal ramification of mycorrhizal fungi; in contrast, in saprobic fungi such as Schizophyllum commune, IAA did not induce morphogenetic changes. Mycorrhiza responded by increasing its Hartig net formation. The IAA of fungal origin acts as a diffusible signal, influencing root colonization and increasing Hartig net formation in ectomycorrhiza. F ungi, mainly basidiomycetes, form a mutually beneficial symbiotic association, commonly known as ectomycorrhiza, with the roots of woody plants (1). After establishing contact with the host, the fungus initially grows around the roots to form a mass of mycelium called the fungal mantle. From there, some hyphae penetrate the roots to grow between cortical cells to form the Hartig net, which acts as a surface for the exchange of nutrients and signals between the two symbiotic partners (1). Variation in host specificity occurs within ectomycorrhizal fungi: some have a broad host range, whereas others form host-specific ectomycorrhiza. In contrast to ectomycorrhizal fungi such as Pisolithus tinctorius and Paxillus involutus, Tricholoma species often show host specificity; their fruiting bodies are found only below compatible host trees. For example, Tricholoma vaccinum fruiting bodies occur only near spruce, which is the compatible host (2). Under laboratory conditions, Tricholoma species form ectomycorrhiza with nonhost trees, but the mycorrhization process in such lowcompatibility interactions requires more time and features spotty Hartig net formation (3). Thus, T. vaccinum, a slow-growing, latestage, and highly host-specific mycorrhizal fungus was chosen for the investigation of fungus-derived phytohormone effects on both partners. These interactions were expected to show the importance of indole-3-acetic acid (IAA) in the establishment and functioning of the symbiosis. We hypothesized that a long period of incubation might be necessary to observe changes in the morphogenetic responses that are not easily visualized with fast-growing, early-stage mycorrhiza. In order to generalize our findin...
SummaryThe C 18 ketone (5E,7E)-6-methyl-8-(2,6,6-trimethylcyclohex-1-enyl)octa-5,7-dien-2-one (D'orenone) has been postulated to be an early cleavage product of b-carotene en route to trisporic acids; these act as morphogenetic factors during the sexual reproduction of zygomycetes. Here we report that D'orenone blocks the highly polarized tip growth of root hairs, causing tip growth to stop completely within a few minutes. Importantly, external auxin reverses the effects of D'orenone on root hairs. Further analysis revealed that D'orenone lowers the auxin concentration in trichoblasts via PIN2-mediated auxin efflux to below the critical levels essential for root hair growth. D'orenone specifically increases PIN2 protein abundance without affecting PIN2 transcripts, and the PIN2 expression domain enlarges and shifts basipetally, resulting in more active auxin transport. The observation that D'orenone does not interfere with the root hair growth in roots of null mutant lines provides additional evidence that PIN2 is its specific target.
The fungal phylum zygomycota uses trisporic acids (TSAs), a family of apocarotenoids, during sexual reproduction to synchronize and control activity between the mycelial hyphae of opposite mating types. Separate as well as mixed cultures of Blakeslea trispora were systematically supplemented with putative, deuterium-labeled precursors downstream of beta-carotene en route to the bioactive TSAs. Analysis of the isolated metabolites allowed the reconstruction of the complete biosynthetic sequence between the first apocarotenoid, D'orenone (1), and the different series of TSAs B (8) and C (13). Both mating types produced a similar spectrum of early metabolites upstream of trisporols B (7) and C (12), while only the (+) type was able to further oxidize trisporols B (7) and C (12) to the corresponding methyltrisporoid B (5) and C (11), respectively. A novel 4-dihydrotrisporic acid B (14) that was not formed from the labeled precursors was isolated from mated strains; this compound might be derived from oxygenated beta-carotene by a parallel pathway. The ester accumulated in the culture broth of the (+) strain and was only hydrolyzed by mycelia of the (-) strain; this corresponds to a synchronization of the biosynthetic activities of both mating types.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.