What makes a specialized endophyte special?

Endophytic fungi associated with Araucaria angustifolia (Bertol.) Kuntze

The diversity of endophytes and their ecological relationships with the endangered conifer Araucaria angustifolia (a critically endangered species) are unrevealed. This study aimed to characterize the diversity of endophytic fungi associated with A. angustifolia. To this end, we analyzed 90 fragments from five individuals collected from a mixed localized fragment in Guarapuava-PR, Brazil. The total DNA of 61 morphotypes was extracted and the Internal Transcribed Spacer (ITS) region was amplified and sequenced. The sequence analysis allowed the identification of 37 genera belonging to the phylum Ascomycota and the classes Eurotiomycetes, Dothideomycetes, and Sordariomycetes, divided into 11 orders and 13 families. Most of the isolated fungi belonged to the Sordariomycetes class (40%) and to the Xylaria genus (14%), while Eurotiomycetes was the minority class within the community. Our results reveal the high endophytic richness supporting the life cycle of A. angustifolia and reinforce the necessity for the conservation of this conifer, as many genetic resources can be lost owing to its irrational exploration.

Host-Species Variation and Environment Influence Endophyte Symbiosis and Mycotoxin Levels in Chinese Oxytropis Species

Oxytropis plants are widely distributed in the grasslands in northern China. Some Oxytropis species have been reported to contain the mycotoxin swainsonine, an alkaloid which causes poisoning in livestock, referred to as locoism. Previous studies showed that endophytic fungi (Alternaria oxytropis) symbiotically associate with these Oxytropis species to produce swainsonine. However, the influence of variation within the Oxytropis genus on the fixation or loss of symbiosis and toxicity is poorly understood, as is the influence of environmental factors. Here we used a collection of 17 common Oxytropis species sampled in northern China to assess genetic diversity using genotyping by sequencing which was compared with the levels of the endophyte and swainsonine. Results showed that nine Oxytropis species have detectable A. oxytropis colonisation, and seven Oxytropis species contain sufficient swainsonine to be considered poisonous, whereas the rest may be non-toxic. Species variation rather than the genetic lineage was associated with the fixation or loss of endophyte and swainsonine production, which appears to have resulted from genetic drift. Genotype × Environment (G × E) effects were also found to influence endophyte and swainsonine levels amongst species of the Oxytropis genus. Our study will provide a better understanding about the evolutionary basis of A. oxytropis symbiosis and swainsonine biosynthesis in locoweeds.

Biosafe Management of Botrytis Grey Mold of Strawberry Fruit by Novel Bioagents

Recently, there have been urgent economic and scientific demands to decrease the use of chemical fungicides during the treatment of phytopathogens, due to their human health and environmental impacts. This study explored the biocontrol efficacy of novel and eco-friendly preen (uropygial) oil and endophytic Bacillus safensis in managing postharvest Botrytis grey mold in strawberry fruit. The preen oil (25 μL/mL) showed high antifungal activity against B. cinerea Str5 in terms of the reduction in the fungal radial growth (41.3%) and the fungal colony-forming units (28.6%) compared to the control. A new strain of Bacillus safensis B3 had a good potential to produce chitinase enzymes (3.69 ± 0.31 U/mL), hydrolytic lipase (10.65 ± 0.51 U/mL), and protease enzymes (13.28 ± 0.65 U/mL), which are responsible for the hydrolysis of the B. cinerea Str5 cell wall and, consequently, restrict fungal growth. The in vivo experiment on strawberry fruit showed that preen (uropygial) oil reduced the disease severity by 87.25%, while the endophytic bacteria B. safensis B3 reduced it by 86.52%. This study reports the efficiency of individually applied bioagents in the control of phytopathogenic fungi for the first time and, consequently, encourages their application as a new and innovative strategy for prospective agricultural technology and food safety.

Mycosynthesis of novel lactone in foliar endophytic fungus isolated from Bixa orellana L

There is a colossal demand for natural pigments and its applications in recent times. In the study, a novel lactone pigment was isolated from a predominant endophytic fungus residing in Bixa orellana L. (Bixaceae) leaves. The endophyte was identified as Fusarium verticillioides through morphological and molecular investigations. The optimum growth parameters of the endophyte for pigment production were at 33 ºC with pH 6.5 in dark. Through comprehensive spectroscopic studies, the structure of the isolated lactone was resolved and identified as (E)-3, 3-dimethyl-4-(pent-1-en-1-yl)-4-propyldihydrofuran-2(3H)-one. The acute oral toxicity study of the pigment investigated upon female Wistar rats indicated the median lethal dose (LD₅₀) value above 1000 mg/kg body weight affirming safety. Thus, the red pigment from the isolated endophyte may be employed as a sustainable source for natural colorant in industries owing to its non-toxicity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02566-x.

The variability of bacterial communities in both the endosphere and ectosphere of different niches in Chinese chives (Allium tuberosum)

Deciphering the various types of interactions between plants and their microbiomes is a hot topic for research in ecology as well as in plant sciences and agronomy. To analyse and compare the differences in microbial communities in different compartments of Chinese chives, high-throughput sequencing technology was employed to amplify and sequence the V5-V6 region of the 16S rDNA of microorganisms in the leaves, phylloplanes, stems, roots and rhizospheres of Chinese chives. The sequences were clustered by operational taxonomic units (OTUs), and the community composition of bacteria between the endosphere (inner tissues) and ectosphere (outer surfaces) of Chinese chives was analysed based on the OTU. Overall, the results indicated that the endophytic bacteria in Chinese chives mainly include Proteobacteria, Actinobacteria, and Actinomycetes. Alpha diversity index analysis and OTU number analysis showed that the bacterial diversity and richness of the underground plant compartments were higher than those of the above-ground parts. PCoA based on the OTU level showed that the vertical stratification structure of plants and compartments had significant effects on the bacterial community structure. The richness of endophytic bacteria also varied greatly among the different varieties of Chinese chive. A considerable number of endophytic bacteria form symbiotic and mutually beneficial relationships with host plants, which play an important role in regulating host growth, metabolism and stress resistance. Further investigations are needed to uncover the evolution of interactions between plants and endophytes.

Host Genotype and Precipitation Influence of Fungal Endophyte Symbiosis and Mycotoxin Abundance in a Locoweed

Many plant endophytes produce mycotoxins, but how host genetic variation influences endophyte colonization and mycotoxin production under natural conditions is poorly understood. This interaction has not been fully considered in many previous studies which used controlled experiments with agronomic or model plant species. Here, we investigated this interaction in a naturally occurring forb (a locoweed species) Oxytropis ochrocephala, its symbiotic endophyte Alternaria oxytropis, and the mycotoxin swainsonine. Host genetic variation was characterized by microsatellite markers. Endophyte infection rate and swainsonine levels were determined by PCR and HPLC, respectively. Genetic markers defined two distinct host populations and revealed that host genetics were significantly correlated with geographical location, elevation, and precipitation. As the host diverged, symbiotic interactions were reduced or failed to produce detectable swainsonine in one host population. Host genotype and precipitation had a significant impact in shaping swainsonine production at the population level. This study highlights the effect of host genotype in influencing this interaction in locoweeds.

Assortative mating in sympatric ascomycete fungi revealed by experimental fertilizations

Mate recognition mechanisms resulting in assortative mating constitute an effective reproductive barrier that may promote sexual isolation and speciation. While such mechanisms are widely documented for animals and plants, they remain poorly studied in fungi. We used two interfertile species of Epichloë (Clavicipitaceae, Ascomycota), E. typhina and E. clarkii, which are host-specific endophytes of two sympatrically occurring grasses. The life cycle of these obligatory outcrossing fungi entails dispersal of gametes by a fly vector among external fungal structures (stromata). To test for assortative mating, we mimicked the natural fertilization process by applying mixtures of spermatia from both species and examined their reproductive success. Our trials revealed that fertilization is non-random and preferentially takes place between conspecific mating partners, which is indicative of assortative mating. Additionally, the viability of hybrid and non-hybrid ascospore offspring was assessed. Germination rates were lower in E. clarkii than in E. typhina and were reduced in ascospore progeny from treatments with high proportions of heterospecific spermatia. The preferential mating between conspecific genotypes and reduced hybrid viability represent important reproductive barriers that have not been documented before in Epichloë. Insights from fungal systems will deepen our understanding of the evolutionary mechanisms leading to reproductive isolation and speciation.