Myosins FaMyo2B and Famyo2 Affect Asexual and Sexual Development, Reduces Pathogenicity, and FaMyo2B Acts Jointly with the Myosin Passenger Protein FaSmy1 to Affect Resistance to Phenamacril in Fusarium asiaticum

Comparative acetylome analysis reveals the potential roles of lysine acetylation for DON biosynthesis in Fusarium graminearum

Background

Fusarium graminearum is a destructive fungal pathogen of wheat, barley and other small grain cereals. During plant infection, the pathogen produces trichothecene mycotoxin deoxynivalenol (DON), which is harmful to human and livestock. FgGCN5 encodes a GCN5 acetyltransferase. The gene deletion mutant Fggcn5 failed to produce DON. We assumed that lysine acetylation might play a key regulatory role in DON biosynthesis in the fungus.

Results

In this study, the acetylome comparison between Fggcn5 mutant and wild-type strain PH-1 was performed by using affinity enrichment and high resolution LC-MS/MS analysis. Totally, 1875 acetylated proteins were identified in Fggcn5 mutant and PH-1. Among them, 224 and 267 acetylated proteins were identified exclusively in Fggcn5 mutant and PH-1, respectively. Moreover, 95 differentially acetylated proteins were detected at a significantly different level in the gene deletion mutant:43 were up-regulated and 52 were down-regulated. GO enrichment and KEGG-pathways enrichment analyses revealed that acetylation plays a key role in metabolism process in F. graminearum.

Conclusions

Seeing that the gens playing critical roles in DON biosynthesis either in Fggcn5 mutant or PH-1. Therefore, we can draw the conclusion that the regulatory roles of lysine acetylation in DON biosynthesis in F. graminearum results from the positive and negative regulation of the related genes. The study would be a foundation to insight into the regulatory mechanism of lysine acetylation on DON biosynthesis.

Phenamacril is a reversible and noncompetitive inhibitor of Fusarium class I myosin

The cyanoacrylate compound phenamacril (also known as JS399-19) is a recently identified fungicide that exerts its antifungal effect on susceptible Fusarium species by inhibiting the ATPase activity of their myosin class I motor domains. Although much is known about the antifungal spectrum of phenamacril, the exact mechanism behind the phenamacril-mediated inhibition remains to be resolved. Here, we describe the characterization of the effect of phenamacril on purified myosin motor constructs from the model plant pathogen and phenamacril-susceptible species Fusarium graminearum, phenamacril-resistant Fusarium species, and the mycetozoan model organism Dictyostelium discoideum Our results show that phenamacril potently (IC50 ∼360 nm), reversibly, and noncompetitively inhibits ATP turnover, actin binding during ATP turnover, and motor activity of F. graminearum myosin-1. Phenamacril also inhibits the ATPase activity of Fusarium avenaceum myosin-1 but has little or no inhibitory effect on the motor activity of Fusarium solani myosin-1, human myosin-1c, and D. discoideum myosin isoforms 1B, 1E, and 2. Our findings indicate that phenamacril is a species-specific, noncompetitive inhibitor of class I myosin in susceptible Fusarium sp.

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.

Resistance risk assessment of Fusarium oxysporum f. sp. melonis against phenamacril, a myosin inhibitor

Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (FOM) is one of the most notorious seed-borne diseases worldwide. Phenamacril is a cyanoacrylate fungicide with novel chemical structure and strong inhibitive activity against FOM. To evaluate the risk of FOM developing phenamacril resistance, five phenamacril-resistant mutants with >800μgml^-1 minimum inhibitory concentration were obtained by repeated exposure to the fungicide in the laboratory. Compared with the parental isolate, four of the five phenamacril-resistant mutants showed enhanced biological fitness in sporulation and virulence, but not in sensitivity to various stresses (oxidative and osmotic pressure, cell membrane and wall inhibitor). No positive cross-resistance was observed among phenamacril and the other five fungicides, including azoxystrobin, carbendazim, boscalid, fluazinam and tebuconazole. Sequencing alignment results of the myosin 5 from the five resistant mutants and the parental strain indicated that the three resistant mutants fo-2, fo-3 and fo-4 had a single point mutation (S175L), which may confer the resistance of FOM against phenamacril. Interestingly, the resistant mutant fo-4 harbored not only one mutation (S175L) at myosin 5, but also the other mutation (A52G) at β₂-tublin. Our data supported that resistance risk of Fusarium oxysporum f. sp. melonis against phenamacril was between the moderate to high level.

The fungal myosin I is essential for Fusarium toxisome formation

Myosin-I molecular motors are proposed to function as linkers between membranes and the actin cytoskeleton in several cellular processes, but their role in the biosynthesis of fungal secondary metabolites remain elusive. Here, we found that the myosin I of Fusarium graminearum (FgMyo1), the causal agent of Fusarium head blight, plays critical roles in mycotoxin biosynthesis. Inhibition of myosin I by the small molecule phenamacril leads to marked reduction in deoxynivalenol (DON) biosynthesis. FgMyo1 also governs translation of the DON biosynthetic enzyme Tri1 by interacting with the ribosome-associated protein FgAsc1. Disruption of the ATPase activity of FgMyo1 either by the mutation E420K, down-regulation of FgMyo1 expression or deletion of FgAsc1 results in reduced Tri1 translation. The DON biosynthetic enzymes Tri1 and Tri4 are mainly localized to subcellular structures known as toxisomes in response to mycotoxin induction and the FgMyo1-interacting protein, actin, participates in toxisome formation. The actin polymerization disruptor latrunculin A inhibits toxisome assembly. Consistent with this observation, deletion of the actin-associated proteins FgPrk1 and FgEnd3 also results in reduced toxisome formation. Unexpectedly, the FgMyo1-actin cytoskeleton is not involved in biosynthesis of another secondary metabolite tested. Taken together, this study uncovers a novel function of myosin I in regulating mycotoxin biosynthesis in filamentous fungi.

The mycotoxin deoxynivalenol (DON) is the most frequently detected secondary metabolite produced by Fusarium graminearum and other Fusarium spp. To date, relatively few studies have addressed how mycotoxin biosynthesis occurs in fungal cells. Here we found that myosin I governs translation of DON biosynthetic enzyme Tri1 via interacting with the ribosome-associated protein FgAsc1. Moreover, the key DON biosynthetic enzymes Tri1 and Tri4 are mainly localized to the toxisomes derived from endoplasmic reticulum under toxin inducing conditions. We further found that the FgMyo1-actin cytoskeleton was involved in toxisome formation but not for the biosynthesis of another secondary metabolite tested. Taken together, these results indicate for the first time that myosin I plays critical roles in mycotoxin biosynthesis.