Clohesyomyces symbioticus sp. nov., a fungal endophyte associated with roots of water smartweed (Persicaria amphibia)

The widespread aquatic plant Persicaria amphibia (water smartweed, Polygonaceae) occurs in both flooded aquatic habitats and moist terrestrial environments. Its physiological versatility and wide geographic range highlight its resilience to stress and make the species intriguing for the study of fungal endophytes. Endophytes occur within living plant tissues and are known from diverse aquatic, marine, and terrestrial plants, where they often mitigate plant responses to stress. As part of a study evaluating endophyte communities associated with aquatic plants in lentic waters of Arizona, USA, we isolated a distinctive clade of endophytes from healthy, living roots of seasonally inundated P. amphibia, which we describe here on the basis of morphology and evidence from four loci as new species Clohesyomyces symbioticus (Lindgomycetaceae, Pleosporales, Dothideomycetes, Ascomycota). Clohesyomyces has long been considered a monotypic genus comprising the saprobic species C. aquaticus, presently known from submerged wood in freshwater systems in Asia and Australia. Description of Clohesyomyces symbioticus highlights the occurrence of endophytism in this genus and expands its geographic scope to the western hemisphere.

Endophytic fungal association in roots of exotic medicinal plants cultivated in the Nilgiris, Western Ghats, Peninsular India

Algunos microbios beneficiosos para el suelo ayudan en el establecimiento y crecimiento de plantas medicinales exóticas. Por lo tanto, evaluamos la presencia y el estado de la asociación de endófitos de raíces [hongos micorrízicos arbusculares (AM) y hongos endofíticos septados oscuros (DSE)] en diez especies de plantas medicinales exóticas cultivadas en Nilgiris de los Ghats occidentales. El alcance de las variables endófitas de hongos y las características del pelo de la raíz difirieron significativamente entre las plantas medicinales. Se identificaron seis morfotipos de esporas de hongos AM en las muestras de suelo. Por lo tanto, este estudio indicó la asociación de plantas medicinales exóticas con hongos nativos AM y DSE que podrían explotarse para promover el crecimiento y aumentar la producción de metabolitos secundarios en estas especies de plantas. Some soil beneficial microbes help in the establishment and growth of exotic medicinal plants. Therefore, we evaluated the presence and status of root endophyte [arbuscular mycorrhizal (AM) fungi and dark septate endophytic (DSE) fungi] association in ten exotic medicinal plant species cultivated in the Nilgiris of the Western Ghats. The AM fungi colonized all the examined plant species and eight plants had the co-occurrence of DSE fungi. The extent of fungal endophyte variables and root hair characteristics significantly differed among the medicinal plants. Six AM fungal spore morphotypes were identified in the soil samples. Thus, this study indicated the association of exotic medicinal plants with native AM and DSE fungi which could be exploited to promote growth and increase secondary metabolite production in these plant species.

A microbial mutualist within host individuals increases parasite transmission between host individuals: Evidence from a field mesocosm experiment

The interactions among host-associated microbes and parasites can have clear consequences for disease susceptibility and progression within host individuals. Yet, empirical evidence for how these interactions impact parasite transmission between host individuals remains scarce. We address this scarcity by using a field mesocosm experiment to investigate the interaction between a systemic fungal endophyte, Epichloe coenophiala, and a fungal parasite, Rhizoctonia solani, in leaves of a grass host, tall fescue. Specifically, we investigated how this interaction impacted parasite transmission under field conditions in replicated experimental host populations. Epichloe-inoculated populations tended to have greater disease prevalence over time, though this difference had weak statistical support. More clearly, Epichloe-inoculated populations experienced higher peak parasite prevalences than Epichloe-free populations. Epichloe conferred a benefit in growth; Epichloe-inoculated populations had greater aboveground biomass than Epichloe-free populations. Using biomass as a proxy, host density was correlated with peak parasite prevalence, but Epichloe still increased peak parasite prevalence after controlling for the effect of biomass. Together, these results suggest that within-host microbial interactions can impact disease at the population level. Further, while Epichloe is clearly a mutualist of tall fescue, it may not be a defensive mutualist in relation to R. solani.

Transcriptional profiles of a foliar fungal endophyte (Pestalotiopsis, Ascomycota) and its endohyphal bacterium (Luteibacter, Gammaproteobacteria) in co-culture support sulfur exchange and growth regulation

Symbiosis with bacteria is widespread among eukaryotes, including fungi. Bacteria that live within fungal mycelia (endohyphal bacteria) occur in many plant-associated fungi, including diverse Mucoromycota and Dikarya. Pestalotiopsis sp. 9143 is a filamentous ascomycete isolated originally as a foliar endophyte of Platycladus orientalis (Cupressaceae). It is infected naturally with the endohyphal bacterium Luteibacter sp. 9143, which influences auxin and enzyme production by its fungal host. Previous studies have used transcriptomics to examine similar symbioses between endohyphal bacteria and root-associated fungi such as arbuscular mycorrhizal fungi and plant pathogens. However, currently there are no gene expression studies of endohyphal bacteria of Ascomycota, the most species-rich fungal phylum. We developed methods for assessing gene expression by Pestalotiopsis sp. and Luteibacter sp. when grown in co-culture and when each was grown axenically. Our assays showed that the density of Luteibacter sp. in co-culture was greater than in axenic culture, but the opposite was true for the Pestalotiopsis sp. Dual RNA-seq data demonstrate that growing in co-culture modulates developmental and metabolic processes in both the fungus and bacterium, potentially through changes in the balance of organic sulfur via methionine acquisition. Our analyses also suggest an unexpected, potential role of the bacterial type VI secretion system in symbiosis establishment, expanding current understanding of the scope and dynamics of fungal-bacterial symbioses.

Development of Plant–Fungal Endophyte Associations to Suppress Phoma Stem Canker in Brassica

Endophytic microorganisms are found within the tissues of many plants species, with some conferring several benefits to the host plant including resistance to plant diseases. In this study, two putative endophytic fungi that were previously isolated from wild seeds of Brassica, identified as Beauveria bassiana and Pseudogymnoascus pannorum, were inoculated into cultivars of three Brassica species—Brassica napus, Br. rapa and Br. oleracea. Both fungal endophytes were reisolated from above- and below-ground tissues of inoculated plants at four different plant-growth stages, including cotyledon, one-leaf, two-leaf, and four-leaf stages. None of the plants colonised by these fungi exhibited any obvious disease symptoms, indicating the formation of novel mutualistic associations. These novel plant–endophyte associations formed between Brassica plants and Be. bassiana significantly inhibited phoma stem canker, a devastating disease of Brassica crops worldwide, caused by the fungal pathogen Leptosphaeria maculans. The novel association formed with P. pannorum significantly suppressed the amount of disease caused by L. maculans in one out of two experiments. Although biological control is not a new strategy, endophytic fungi with both antiinsect and antifungal activity are a highly conceivable, sustainable option to manage pests and diseases of economically important crops.

The Endophytic Fungus Cyanodermella asteris Influences Growth of the Non-Natural Host Plant Arabidopsis thaliana

Cyanodermella asteris is a fungal endophyte from Aster tataricus, a perennial plant from the Northern part of Asia. Here, we demonstrated an interaction of C. asteris with Arabidospis thaliana, Chinese cabbage, rapeseed, tomato, maize or sunflower resulting in different phenotypes such as shorter main roots, massive lateral root growth, higher leaf and root biomass, and increased anthocyanin levels. In a variety of co-cultivation assays, it was shown that these altered phenotypes are caused by fungal CO2, volatile organic compounds, and soluble compounds, notably astins. Astins A, C and G induced plant growth when they were individually included in the medium. In return, A. thaliana stimulates the fungal astin C production during co-cultivation. Taken together, our results indicate a bilateral interaction between the fungus and the plant. A stress response in plants is induced by fungal metabolites while plant stress hormones induced astin C production of the fungus. Interestingly, our results not only show unidirectional influence of the fungus on the plant, but vice versa. The plant is able to influence growth and secondary metabolite production in the endophyte, even when both organisms do not live in close contact, suggesting the involvement of volatile compounds.

Mongolian pine forest decline by the combinatory effect of European woodwasp and plant pathogenic fungi

Interactions between the decline of Mongolian pine woodlands and fungal communities and invasive pests in northeastern China are poorly understood. In this study, we investigated the fungal communities occurring in three tree samples: the woodwasp Sirex noctilio infested, healthy uninfested and unhealthy uninfested Mongolian pine trees. We analyzed the relationships of the Mongolian pine decline with fungal infection and woodwasp infestation. Twenty-six fungal species were identified from the sampled trees. Each tree sample harbored a fungal endophyte community with a unique structure. Pathogenic fungi richness was four times higher in infested and unhealthy un-infested trees compared to that in healthy uninfested trees. Sphaeropsis sapinea was the most dominant pathogenic fungus in the sampled Mongolian pine trees. The number of S. noctilio was higher than native bark beetles in the declining Mongolian pine trees. The invasion of the woodwasp appeared to be promoted by the fungal infection in the Mongolian pine trees. The incidence of S. noctilio infestation was higher in the fungi infected trees (83.22%) than those without infection (38.72%). S. sapinea population exhibited positive associations with within-tree colonization of S. noctilio and bark beetle. Collectively, these data indicate that the fungal disease may have caused as the initial reason the decline of the Mongolian pine trees, and also provided convenient conditions for the successful colonization of the woodwasp. The woodwasps attack the Mongolian pine trees infected by fungi and accelerated its decline.