Extending the Host Range of Fusarium Poae Virus 1 from Fusarium poae to other Fusarium Species in the Field.

Fusarium poae virus 1 (FpV1, a betapartitivirus) is one of the mycoviruses which is discovered earlier. Due to the vegetative incompatibility barrier that often exists between different species or strains of filamentous fungi, FpV1 has been thought to be limited to its host, F. poae, as a non-hypovirulence mycovirus in the past 20 years in the field. Here, a novel strain of FpV1 (FpV1-Fa) with two dsRNA segments (2157-and 2080-nt) was consistently identified in F. asiaticum isolates in the field. FpV1-Fa induced abnormal morphology and hypovirulence of F. asiaticum, along with a high viral load. FpV1-Fa was detected only from the F. asiaticum and F. tricinctum strains at a FpV1-Fa sampling site (119.014289, 33.8261), while the other strains from other sites were not identified FpV1-Fa. A horizontal transmission experiment showed that FpV1-Fa can transfer from F. asiaticum to F. poae and F. tricinctum, but not to F. graminearum. The selection analysis of FpV1-Fa revealed RdRP and CP were under strong purifying selection, and the C-terminal side of RdRP was under positive selection. In these regions, 9 amino acid mutations in RdRP and 21 mutations in CP appeared to cause the variation of host range and virulence in FpV1-Fa.

Risk assessment of mercury through dietary exposure in China.

Mercury (Hg) is a widespread heavy metal causing various damages to health, while insufficient studies assessed its exposure risk across China. This study explored concentrations in food items and dietary exposure risks across China by comprehensively analyzing the researches on total Hg (THg) in eight food items and methylmercury (MeHg) in aquatic foods published between 1980 and 2021. According to the included 695 studies, the average THg concentration in all food items was 0.033 mg/kg (ranging from 0.004 to 0.185 mg/kg), with the highest concentration in edible fungi. The average daily dietary THg exposure from all foods was 12.9 µg/day. Plant-based foods accounted for 62.7% of the dietary THg exposure. Cereals and vegetables were the primary source of THg exposure. The MeHg concentration in aquatic foods was 0.08 mg/kg, and the average dietary exposure was 3.8 µg/day. Monte Carlo simulations of the dietary exposure risk assessment of THg and MeHg showed that approximately 6.4 and 7.0% of residents exceeded the health-based guidance value set by the European Food Safety Authority, with higher exposure risk in Southwest and South China. The nationwide target hazard quotient index of THg was greater than 1, suggesting that the non-carcinogenic risk of dietary exposure to THg needed further concern. In summary, this study has a comprehensive understanding of dietary Hg exposure risks across China, which provide a data basis for Hg exposure risk assessment and policy formulation.

The ASK1 gene regulates the sensitivity of Fusarium graminearum to carbendazim, conidiation and sexual production by combining with ß2-tubulin.

ß-tubulin, a component of microtubules, is involved in a wide variety of roles in cell shape, motility, intracellular trafficking and regulating intracellular metabolism. It has been an important fungicide target to control plant pathogen, for example, Fusarium. However, the regulation of fungicide sensitivity by ß-tubulin-interacting proteins is still unclear. Here, ASK1 was identified as a ß-tubulin interacting protein. The ASK1 regulated the sensitivity of Fusarium to carbendazim (a benzimidazole carbamate fungicide), and multiple cellular processes, such as chromatin separation, conidiation and sexual production. Further, we found the point mutations at 50th and 198th of ß2-tubulin which caused carbendazim resistance decreased the binding between ß2-tubulin and ASK1, resulting in the deactivation of ASK1. ASK1, on the other hand, competed with carbendazim to bind to ß2-tubulin. The point mutation F167Y in ß2-tubulin broke the intermolecular H-bonds and salt bridges between ß2-tubulin and ASK1, which reduced the competitive effect of ASK1 to carbendazim and resulted in the similar carbendazim sensitivities in F167Y-ΔASK1 and F167Y. These findings have powerful implications for efforts to understand the interaction among ß2-tubulin, its interacting proteins and fungicide, as well as to discover and develop new fungicide against Fusarium.

Ethylenediaminetetraacetic Acid Disodium Salt Acts as an Antifungal Candidate Molecule against Fusarium graminearum by Inhibiting DON Biosynthesis and Chitin Synthase Activity.

Fusarium fungi are the cause of an array of devastating diseases affecting yield losses and accumulating mycotoxins. Fungicides can be exploited against Fusarium and deoxynivalenol (DON) production. However, Fusarium resistance to common chemicals has become a therapeutic challenge worldwide, which indicates that new control agents carrying different mechanisms of action are desperately needed. Here, we found that a nonantibiotic drug, ethylenediaminetetraacetic acid disodium salt (EDTANa2), exhibited various antifungal activities against Fusarium species and DON biosynthesis. The infection of wheat seeding caused by F. graminearum was suppressed over 90% at 4 mM EDTANa2. A similar control effect was observed in field tests. Mycotoxin production assays showed DON production was significantly inhibited, 47% lower than the control, by 0.4 mM EDTANa2. In vitro experiments revealed a timely inhibition of H2O2 production as quickly as 4 h after amending cultures with EDTANa2 and the expression of several TRI genes significantly decreased. Chitin synthases of Fusarium were Mn2+-containing enzymes that were strongly inhibited by Mn2+ deficiency. EDTANa2 inhibited chitin synthesis and destroyed the cell wall and cytomembrane integrity of Fusarium, mainly via the chelation of Mn2+ by EDTANa2, and thus led to Mn deficiency in Fusarium cells. Taken together, these findings uncover the potential of EDTANa2 as a fungicide candidate to manage Fusarium head blight (FHB) and DON in agricultural production.

A ß2-tubulin dsRNA derived from Fusarium asiaticum confers plant resistance to multiple phytopathogens and reduces fungicide resistance.

Crops are attacked by a large number of pathogens which are responsible for an approximately 30% loss in global crop production at pre- and post-harvest levels. In light of the continuing emergence of fungicide resistance, the needs for new agricultural drugs turn out to be much more critical. Here we demonstrated a Faß2Tub-3 dsRNA derived from Fusarium asiaticum had broad-spectrum antifungal activity against Fusarium spp., Botrytis cinerea, Magnaporthe oryzae and Colletotrichum truncatum, with an additional function of reducing the dosage of carbendazim (MBC) fungicide. RNAi molecules derived from different regions of ß2-tubulin gene had different effects on mycelial growth, asexual reproduction and virulence. Faß2Tub-3 (one of ß2-tubulin segments) exhibited a strong silencing efficacy both on ß1-tubulin and ß2-tubulin genes in F. asiaticum. Faß2Tub-3 sequence was found to be highly conserved among Fusarium spp., Botrytis cinerea, Magnaporthe oryzae and Colletotrichum truncatum. The Faß2Tub-3 dsRNA demonstrated a broad-spectrum antifungal activity against these fungi in vitro and on living plant. More importantly, Faß2Tub-3 dsRNA increased the fungal sensitivity to MBC, while MBC increased the duration of Faß2Tub-3 dsRNA. Our findings suggest a new anti-fungal agent (Faß2Tub-3 dsRNA) for plant protection against diverse pathogens and for fungicide reduction.

A myosin5 dsRNA that reduces the fungicide resistance and pathogenicity of Fusarium asiaticum.

Fungal resistance to fungicides is a serious challenge in crop protection. Although strategies have been found to prevent the development of fungicide resistance, rare strategy has been found to quickly reduce such resistance once it has occurred. We demonstrate that the application of dsRNAs, which inhibit the expression of the phenamacril (fungicide JS399-19) target gene-Myosin 5 (Myo5) in Fusarium, decreased F. asiaticum resistance to phenamacril and infection. RNAi molecules derived from different regions of Myo5 gene had different effects on phenamacril-resistance. Myo5-8 (one of Myo5 segments) exhibited great and stable effect on phenamacril-resistant reduction both in vivo and in vitro. Myo5 mRNA and protein were both reduced when mycelium was treated with Myo5-8 dsRNA. After a mixture of Myo5-8 dsRNA and phenamacril treatment, plants can highly control the infection of phenamacril-resistant strain. The antifungal activity of Myo5-8 dsRNA plus phenamacril effected longer than a single Myo5-8 dsRNA. In addition, no off-target sequences were found in wheat and/or other plant and animal species for Myo5-8 dsRNA sequence. Our findings suggest a new strategy for fungicide resistant reduction and for designing new fungicides to control pathogens which easily develop fungicide resistance.

Secondary amplification of siRNA machinery limits the application of spray-induced gene silencing.

Spray-induced gene silencing (SIGS) is an innovative strategy for crop protection. However, the mechanism of SIGS is not known. Here, we first demonstrate that secondary small interfering RNA (siRNA) amplification limits the application of SIGS. A myosin5 gene (Myo5) was chosen as the target of SIGS in an agronomically important pathogen-Fusarium asiaticum. Five segments corresponding to the different regions of the Myo5 gene were found to efficiently silence Myo5, resulting in cell wall defects, life cycle disruption and virulence reduction. Myo5-8 (one of the Myo5 segments) induced sequence-specific RNA interference (RNAi) activity in F. asiaticum, F. graminearum, F. tricinctum and F. oxysporum, but not in other fungi, in vitro. Remarkably, the silencing of Myo5 lasted for only 9 h unless the double-stranded RNA (dsRNA) was continuously supplied, because F. asiaticum is unable to maintain siRNA amplification. After spraying on plants, dsRNAs were more efficiently taken up via the wounded surface. The antifungal activity of dsRNAs taken up by plant cells was higher and longer lasting than that dried onto the plant surface. In contrast with dsRNAs in fungi, dsRNAs in plant cells could efficiently turn into substantial siRNAs via secondary amplification machinery. Our findings provide new implications to develop SIGS as a mainstream disease control strategy against Fusarium and other fungi.