Molecular and Biological Characterization of the First Mymonavirus Identified in Fusarium oxysporum

We characterized a negative sense single-stranded RNA mycovirus, Fusarium oxysporum mymonavirus 1 (FoMyV1), isolated from the phytopathogenic fungus Fusarium oxysporum. The genome of FoMyV1 is 10,114 nt, including five open reading frames (ORFs1–5) that are non-overlapping and linearly arranged. The largest, ORF5, encodes a large polypeptide L containing a conserved regions corresponding to Mononegavirales RNA-dependent RNA polymerase and mRNA-capping enzyme region V; the putative functions of the remaining four ORFs are unknown. The L protein encoded by ORF5 shared a high amino acid identity of 65% with that of Hubei rhabdo-like virus 4, a mymonavirus that associated with arthropods. However, the L protein of FoMyV1 also showed amino acid similarity (27–36%) with proteins of mynonaviruses that infect the phytopathogenic fungi Sclerotinia sclerotiorum and Botrytis cineaea. Phylogenetic analysis based on L protein showed that FoMyV1 is clustered with the members of the genus Hubramonavirus in the family Mymonaviridae. Moreover, we found that FoMyV1 could successfully transfer by hyphal anastomosis to a virus-free strain. FoMyV1 reduced the vegetative growth and conidium production of its fungal host but did not alter its virulence. To the best of our knowledge, this is not only the first mymonavirus described in the species F. oxysporum, but also the first Hubramonavirus species found to infect a fungus. However, the incidence of FoMyV1 infections in the tested F. oxysporum strains was only 1%.

Flowerlike Ni-NiO composite as magnetic solid-phase extraction sorbent for analysis of carbendazim and thiabendazole in edible vegetable oils by liquid chromatography-mass spectrometry

A rapid, selective, and sensitive method was developed for the detection of carbendazim and thiabendazole in edible vegetable oil. Two benzimidazole analytes were pre-concentrated by magnetic solid phase extraction (MSPE) using flowerlike Ni-NiO composite as sorbents and followed by LC-MS/MS analysis. The flowerlike Ni-NiO composite sorbent displayed a high affinity towards benzimidazole analytes due to the reversible coordination interaction between the Ni(Ⅱ) ion and the electron-donating imidazole group. In comparison to the previous methods, this procedure is less time-consuming and simpler during sample preparation. The parameters affecting the extraction efficiency were optimized in detail. The method was validated according to SANTE/12682/2019. The limits of detection were in the range of 0.001-0.003 mg•kg^-1. The recoveries ranged from 89.3% to 110.7% with inter-day and inter-day precision less than 10.9%. The results indicate that flowerlike Ni-NiO composite might be a promising alternative for MSPE of benzimidazole compounds in foods.

Discovery of new vascular disrupting agents based on evolutionarily conserved drug action, pesticide resistance mutations, and humanized yeast

Thiabendazole (TBZ) is an FDA-approved benzimidazole widely used for its antifungal and antihelminthic properties. We showed previously that TBZ is also a potent vascular disrupting agent and inhibits angiogenesis at the tissue level by dissociating vascular endothelial cells in newly formed blood vessels. Here, we uncover TBZ's molecular target and mechanism of action. Using human cell culture, molecular modeling, and humanized yeast, we find that TBZ selectively targets only 1 of 9 human β-tubulin isotypes (TUBB8) to specifically disrupt endothelial cell microtubules. By leveraging epidemiological pesticide resistance data and mining chemical features of commercially used benzimidazoles, we discover that a broader class of benzimidazole compounds, in extensive use for 50 years, also potently disrupt immature blood vessels and inhibit angiogenesis. Thus, besides identifying the molecular mechanism of benzimidazole-mediated vascular disruption, this study presents evidence relevant to the widespread use of these compounds while offering potential new clinical applications.

Activity of a novel succinate dehydrogenase inhibitor fungicide pyraziflumid against Sclerotinia sclerotiorum

Pyraziflumid is a novel member of succinate dehydrogenase inhibitor fungicides (SDHI). In this study, baseline sensitivity of Sclerotinia sclerotiorum (Lib.) de Bary to pyraziflumid was determined using 105 strains collected during 2015 and 2017 from different geographical regions in Jiangsu Province of China, and the average EC₅₀ value was 0.0561 (±0.0263)μg/ml for mycelial growth. There was no cross-resistance between pyraziflumid and the widely used fungicides carbendazim, dimethachlon and the phenylpyrrole fungicide fludioxonil. After pyraziflumid treated, hyphae were contorted with offshoot of top increasing, cell membrane permeability increased markedly, oxalic acid content significantly decreased and mycelial respiration was strongly inhibited. But the number and dry weight of sclerotia did not change significantly. The protective and curative activity test of pyraziflumid suggested that pyraziflumid had great control efficiency against S. sclerotiorum on detached rapeseed leaves, and protective activity was better than curative activity. These results will contribute to us on evaluating the potential of the new SDHI fungicide pyraziflumid for management of diseases caused by S. sclerotiorum and understanding the mode of action of pyraziflumid against S. sclerotiorum.

Hormetic Effects of Trifloxystrobin on Aggressiveness of Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a devastating ascomycete plant pathogen with an extremely wide host range. Fungicides are still the mainstay for control of this pathogen, and stimulations to mycelial growth and aggressiveness by subtoxic doses of fungicides carbendazim and dimethachlon have been reported. The present study assessed hormetic effects of the quinone outside inhibitor (QoI) fungicide trifloxystrobin on aggressiveness of S. sclerotiorum. Trifloxystrobin at 0.0001, 0.0005, and 0.001 μg/ml exerted significant stimulatory effects on aggressiveness to potted rapeseed plants, and the highest percent stimulation were 20.5 and 24.2% for isolates HB15 and SX11, respectively. At 18 h postinoculation (HPI), initial necrotic lesions were visible to the naked eye on leaves treated with trifloxystrobin, whereas no obvious disease symptoms were discerned for the nontreated control. At 24, 36, and 48 HPI, aggressiveness stimulation was more obvious than at 18 HPI. Scanning electron microscopic observations demonstrated that no mycelia were detected on the nontreated leaves at 4 HPI; by contrast, mycelia were observed on leaves treated with trifloxystrobin at 0.0001 μg/ml. At 8 and 12 HPI, there were more mycelia and infecting hyphae on the treated leaves than on the nontreated control. These results indicated that fungal stimulation had occurred in the first 4 and 8 HPI, suggesting that direct stimulation was likely to be the underlying mechanism for hormetic actions of trifloxystrobin. Pretreatment with trifloxystrobin did not significantly affect subsequent mycelial growth on PDA or aggressiveness to detached rapeseed leaves in the absence of trifloxystrobin. However, in the presence of trifloxystrobin, mycelial growth and aggressiveness were significantly (P < 0.05) greater for the pretreatment with trifloxystrobin at 0.003 and 0.03 μg/ml compared with the nonpretreatment control, indicating that a prior exposure to the fungicide may undermine its subsequent effectiveness. These studies will raise our awareness of fungicide hormesis and have important implications for judicious application of fungicides.