Molecular crosstalk between the endophyte Paraconiothyrium variabile and the phytopathogen Fusarium oxysporum – Modulation of lipoxygenase activity and beauvericin production during the interaction

Abstract

Plants comprise many asymptomatic fungal endophytes with potential roles of plant protection against abiotic and biotic stresses. Endophytes communicate with their host plant, with other endophytes and with invading pathogens but their language remains largely unknown. This work aims at understanding the chemical communication and physiological interactions between the fungal endophyte Paraconiothyrium variabile and the phytopathogen Fusarium oxysporum. Oxylipins, common means of communication, such as 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), had been shown in our earlier studies to be overproduced during dual culture between the two fungal antagonists. On the other hand, the mycotoxin beauvericin was reduced in the interaction zone. The present work addresses the mechanisms underlying these changes. Hydroperoxy oxylipins are produced by lipoxygenases and P. variabile contains two lipoxygenase genes (pvlox1 and pvlox2), whereas pvlox2, but not pvlox1, is specifically up regulated during the interaction and none of the F. oxysporum lox genes vary. Heterologous expression of pvlox2 in yeast shows that the corresponding enzyme PVLOX2 produces 13-HPODE and, therefore, is most likely at the origin of the overproduced 13-HPODE during the interaction. Compellingly, beauvericin synthase gene beas expression is induced and beauvericin amounts increase in F. oxysporum mycelium when in contact with P. variabile. 13-HPODE, however, does not affect beas gene expression. Beauvericin, indeed, inhibits P. variabile growth, which counteracts and biotransforms the mycotoxin leading to reduced amounts in the interaction zone which allows further expansion of the endophyte. In order to study the interaction between the protagonists in planta, we set up an in vitro tripartite interaction assay, including the model plant Arabidopsis thaliana. F. oxysporum rapidly kills A. thaliana plants, whereas P. variabile provides up to 85% reduction of plant death if present before pathogen attack. Future studies will shed light on the protection mechanisms and the role of oxylipins and beauvericin degradation herein with the long-term aim of using endophytes in plant protection.

Co‑cultivation of the anaerobic fungus Caecomyces churrovis with Methanobacterium bryantii enhances transcription of carbohydrate binding modules, dockerins, and pyruvate formate lyases on specific substrates

“…A previous study showed that anaerobic fungal genomes encode a wide array of biosynthetic enzymes of natural products including secondary metabolitessmall, bioactive molecules known to mediate a variety of interactions between microorganisms [54][55][56][57]. The majority of these genes were not significantly differentially expressed between co-culture and monoculture conditions on the various substrates in this study.…”

Cocultivation of Anaerobic Fungi with Rumen Bacteria Establishes an Antagonistic Relationship

“…Secondary metabolites, although not strictly necessary for the growth or survival of an organism under all growth conditions ( 22 ), are often secreted during antagonistic relationships between microorganisms ( 23 – 25 ). Previous work mining the high-quality genomes of anaerobic fungi revealed that anaerobic fungi are capable of synthesizing secondary metabolites ( 26 ).…”

Anaerobic gut fungi are an untapped reservoir of natural products

“…We hypothesize that anaerobic gut fungi synthesize natural products to compete with other microbes for survival in their native environment. Natural products are known to serve a variety of functions to their producers in other environments, including oxidative stress tolerance ( 16 ), fungal development ( 17 ), and antibiosis ( 18 ). Similarly, the natural products of anaerobic gut fungi may serve directly (by antibiosis) or indirectly (by conferring environmental stress tolerance) to allow the fungi to persist despite being outnumbered by other members of the rumen community.…”