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Chapter 38 : Fusarium Genetics and Pathogenicity
Category: Microbial Genetics and Molecular Biology; Fungi and Fungal Pathogenesis
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Various members of the Fusarium genus are associated with plant diseases and the production of various classes of mycotoxins, with many secondary metabolites still only poorly characterized. The conditionally dispensable chromosome of F. solani appears to contain many pea pathogenicity genes that are important for host range determinants but are dispensable for normal growth in culture. Several well-conserved signal transduction pathways have been studied in some Fusarium species. Mitogen-activated protein kinase (MAPK) genes homologous to the M. grisea PMK1 have been characterized in F. oxysporum (FMK1) and F. graminearum (GPMK1/MAK1). All of the sequenced Fusarium genomes contain multiple copies of genes encoding cutinases, xylanases, polygalacturonases (PG), and other cell wall-degrading enzyme (CWDE) genes, indicating the importance of these hydrolytic enzymes. Fusarium head scab has been linked to deoxynivalenol (DON) in two ways. First there were mechanistic studies conducted by researchers showing that strains that produced more DON were more aggressive than strains that produced nivalenol as an alternative to DON or that produced no trichothecenes whatsoever. Second, in a quantitative trait locus analysis, another group of researchers showed that the cluster of genes responsible for trichothecene biosynthesis was at the heart of the only major quantitative trait locus in a cross between fungal strains that differed in their ability to cause fusarium head scab. Genetics- and genomics-based approaches will certainly further improve our understanding of molecular mechanisms and evolution of Fusarium pathogenesis.
Key Concept Ranking
- Single Nucleotide Polymorphism Analysis
Spore morphology characters used in the identification of Fusarium species. Drawings are idealized and not necessarily to scale. (A through D) Macroconidial shapes. (A) Typical Fusarium macroconidium; the apical cell is on the left, and the basal cell is on the right; (B) slender, straight, almost needle-like macroconidium, e.g., F. avenaceum; (C) macroconidium with dorsoventral curvature, e.g., F. equiseti; (D) macroconidium with the dorsal side more curved than the ventral, e.g., F. crookwellense. (E through H) Macroconidial apical cell shapes; (E) blunt, e.g., F. culmorum; (F) papillate, e.g., F. sambucinum; (G) hooked, e.g., F. lateritium; (H) tapering, e.g., F. equiseti. (I through L) Macroconidial basal cell shapes; (I) Foot shaped, e.g., F. crookwellense; (J) elongated foot shape, e.g., F. longipes; (K) distinctly notched, e.g., F. avenaceum; (L) barely notched, e.g., F. solani. (M through T) Microconidial spore shapes; (M) oval; (N) two-celled oval; (O) three-celled oval; (P) reniform; (Q) obovoid with a truncate base; (R) pyriform; (S) napiform; (T) globose. (U through X) Phialide morphology; (U) monophialides, e.g., F. solani; (V) monophialides, e.g., F. oxysporum; (W) Polyphialides, e.g., F. polyphialidicum; (X) polyphialides, e.g., F. semitectum. (Y and Z) Microconidial chains; (Y) short chains, e.g., F. nygamai; (Z) long chains, e.g., F. verticillioides. (After Leslie and Summerell, 2006 .)
Perithecia, asci, and ascospores of Haematonectria haematococca, Gibberella zeae, and Gibberella moniliformis. (A) Cluster of perithecia of G. zeae on wheat straw; bar = 200 μm. (B) Perithecia of H. haematonectria on carnation leaf pieces from CLA; bar = 200 μm. (C) Perithecium of G. zeae oozing ascospores in a cirrhus; bar = 200 μm. (D) Perithecium of H. haematococca oozing ascospores in a cirrhus; bar = 200 μm. (E) Asci and ascospores of G. zeae, note three-septate ascospores; bar = 25 μm. (F) Asci and ascospores of H. haematococca; bar = 25 μm. (G) Ascospores of G. moniliformis, note one-septate ascospores; bar = 10 μm. (H) Ascospores of H. haematococca; bar = 10 μm. (After Leslie and Summerell, 2006 .)
Chlamydospores of Fusarium species. (A and B) Single, verrucose chlamydospores of F. solani; (C and D) clustered chlamydospores of F. compactum; (E) chain of verrucose chlamydospores of F. compactum; (F) paired, smooth-walled chlamydospores of F. solani; (G) single, verrucose chlamydospore of F. scirpi; (H) paired, verrucose chlamydospores of F. compactum; (I) clustered, smooth-walled chlamydospores of F. scirpi; (J and L) chains of verrucose chlamydospores of F. compactum; (K) chain of verrucose chlamydospores of F. scirpi. Scale bars: panels A through E, 50 μm; panels F through L, 25 μm. (After Leslie and Summerell, 2006 .)
Genome characteristics of four sequenced Fusarium species a
Some of the best-known secondary metabolites produced by Fusarium spp. a
Some virulence factors characterized in Fusarium species