The finding, published in Fungal Biology and Biotechnology, marks the first time jasmonic acid has been reported from this fungal family and, according to the authors, makes C. asteris the first plant endophyte known so far to synthesize the hormone. Until now, jasmonate production among fungi had only been documented in a handful of phytopathogenic species such as Lasiodiplodia theobromae, Fusarium oxysporum and Fusarium fujikuroi, organisms that use the hormone to manipulate their hosts during infection.

Jasmonic acid is a fatty acid-derived oxylipin that plays a central role in plants, regulating defense responses against herbivores and necrotrophic pathogens, modulating growth and development, and helping plants cope with abiotic stresses such as drought, heat and salinity. It is activated by wounding and pathogen attack, influences flowering time and seed development, and participates together with other hormones in fruit ripening, senescence and root growth. Beyond plants, the compound has been detected in cyanobacteria such as Spirulina, in algae including Chlorella, Gelidium and Scenedesmus, and in the phytopathogenic fungi mentioned above, but its function in fungi remains poorly understood.

The discovery emerged from a broader effort to understand how C. asteris interacts with its host plants. To search for additional phytohormones involved in plant-endophyte interactions, the researchers cultivated the fungus in liquid culture and intensively analyzed the supernatant. Screening the organic extract from a 12-liter culture by preparative HPLC followed by LC-HR-MS and extensive one- and two-dimensional NMR experiments identified jasmonic acid as the main compound of one conspicuous fraction.

The structural assignment rested on complementary lines of evidence. NMR analysis revealed a (Z)-configured pentenyl side chain and a 1,2-trans substitution pattern on the cyclopentanone core, consistent with commercial jasmonic acid standards and published reference data. UHPLC-ESI-HR-MS and MS/MS measurements confirmed the exact mass, with the calculated protonated molecular ion at m/z 211.1329 for the formula C12H18O3 matching the observed value of 211.1333. The absolute configuration could not be determined experimentally, although previous studies described the (-)-form as dominant in the fungus Botryodiplodia theobromae.

Quantification using the internal standard (±)-D5-JA and LC-MS/MS in negative mode showed that the fungus secretes most of the hormone it synthesizes into the surrounding medium. The relative proportion of jasmonic acid in the medium rose from 19 to 40 percent after four weeks of cultivation to 94 to 98 percent after eight weeks, with only very small amounts retained in the hyphae. The authors interpret this secretion pattern as an indication that the hormone functions in the interaction with the host plant rather than within the endophyte itself, a pattern that parallels the way phytopathogenic fungi deploy jasmonates to dampen plant immune responses and facilitate infection.

A key question was whether the fungus builds jasmonic acid the way plants do. In plants, biosynthesis starts from linolenic acid released from plastid membranes, which is oxygenated by lipoxygenase to 13-hydroperoxylinolenic acid, converted by allene oxide synthase and allene oxide cyclase to 12-oxophytodienoic acid, and finally reduced through beta-oxidation steps to jasmonic acid. When the researchers fed C. asteris cultures with linolenic acid at concentrations from 0.1 to 5 millimolar, jasmonic acid production was not significantly induced. Higher linolenic acid concentrations even reduced jasmonic acid levels relative to the solvent control. Strikingly, the solvent DMSO alone increased jasmonic acid 3.6-fold in the medium and 2.2-fold in the hyphae, suggesting that DMSO, possibly by altering membrane fluidity and enzyme accessibility, was the main inducer rather than the precursor itself.

Genome analysis offered a possible explanation. Using the available genome sequence of C. asteris, the team identified candidate genes for enzymes converting the intermediate OPC8 into jasmonic acid, including an acid-thiol ligase, an acetyl-CoA oxidase, an enoyl-CoA hydratase, an acetyl-CoA C-acyl transferase and thioester hydrolases. However, genes encoding the enzymes that transform linolenic acid into OPC8 were absent from the automated annotation, which may explain why feeding the precursor had no effect. Quantitative PCR comparing cultures with high and low jasmonic acid titers showed that one of three putative thioester hydrolase genes, which would catalyze the final release of free jasmonic acid from JA-CoA, was strongly and significantly up-regulated in the high-producing cultures, indicating that at least this last step likely operates in the fungus.

The study also examined how the fungal hormone affects plant growth. In co-cultivation assays with the model plant Arabidopsis thaliana, the JA biosynthesis-deficient mutant aos10-1, which carries a knockout in the allene oxide synthase gene and displays delayed flowering and seed development, was grown alongside the fungus. C. asteris induced flowering and seed development in both the mutant and the wild-type ecotype Col-0, partially rescuing the JA-deficient phenotype. The fungus also elicited its previously described root architecture changes, shortening the main root while triggering a massive increase in lateral root growth, an effect attributed mainly to the fungal auxin. Co-cultivation with the jasmonate signaling mutant jar1-1 produced the same root and flowering phenotype as the wild type. The authors caution that the fungus produces additional substances, and that jasmonic acid derivatives could not be detected in the fungal extracts, so complementary experiments will be needed to confirm that fungal jasmonic acid alone is responsible for the rescue.

Exogenous jasmonic acid also influenced the fungus itself, with the effect depending on the medium. In the complete medium MEA3, the hormone had no influence on biomass production except at the highest tested concentration of 1 millimolar, where a clear inhibition of biomass formation was evident. In the minimal medium MEAlow, biomass decreased with increasing jasmonic acid concentrations, which the authors attribute to toxicity under nutrient-limited conditions. The addition of jasmonic acid has also been shown in earlier work to increase production of the astin C peptide by the fungus, a response thought to support host plants during stress.

The authors emphasize that much remains to be learned. The exact biosynthetic route in C. asteris is unresolved, and feeding experiments with heavy-labeled precursors and intermediates are proposed to clarify whether the fungus uses a pathway distinct from the plant route, perhaps drawing on oleic or linoleic acid as precursors as suggested for other fungal oxylipins. A fungal-specific jasmonate biosynthesis inhibitor, once identified, could be combined with JA-deficient Arabidopsis mutants to demonstrate unambiguously that the rescue of the deficient phenotype stems from fungal jasmonic acid rather than other fungal metabolites. As the first endophyte shown to produce this defense hormone, C. asteris opens a new window on how fungi and plants negotiate their chemical relationship, and on the potential of the fungus as a biological producer of jasmonic acid.

Subject of Research: Biosynthesis and secretion of the phytohormone jasmonic acid by the endophytic fungus Cyanodermella asteris

Article Title: The plant endophytic fungus Cyanodermella asteris produces the phytohormone jasmonic acid

Article References: Jahn, L., Sester, A., Domaschke, E. T., Gulder, T. A. M., & Ludwig-Müller, J. (2026). The plant endophytic fungus Cyanodermella asteris produces the phytohormone jasmonic acid. Fungal Biology and Biotechnology, 13(1), Article 4. https://doi.org/10.1186/s40694-026-00210-6

Image Credits: AI Generated

DOI: 10.1186/s40694-026-00210-6

Keywords: Cyanodermella asteris, jasmonic acid, endophytic fungus, phytohormones, plant-fungus interaction, Arabidopsis thaliana, LC-MS/MS, NMR, biosynthesis, linolenic acid, Aster tataricus, fungal metabolism