Characterisation of pathogen-specific regions and novel effector candidates in Fusarium oxysporum f. sp. cepae

A reference-quality assembly of Fusarium oxysporum f. sp. cepae (Foc), the causative agent of onion basal rot has been generated along with genomes of additional pathogenic and non-pathogenic isolates of onion. Phylogenetic analysis confirmed a single origin of the Foc pathogenic lineage. Genome alignments with other F. oxysporum ff. spp. and non pathogens revealed high levels of syntenic conservation of core chromosomes but little synteny between lineage specific (LS) chromosomes. Four LS contigs in Foc totaling 3.9 Mb were designated as pathogen-specific (PS). A two-fold increase in segmental duplication events was observed between LS regions of the genome compared to within core regions or from LS regions to the core. RNA-seq expression studies identified candidate effectors expressed in planta, consisting of both known effector homologs and novel candidates. FTF1 and a subset of other transcription factors implicated in regulation of effector expression were found to be expressed in planta

The Nuclear Protein Sge1 of Fusarium oxysporum Is Required for Parasitic Growth

Dimorphism or morphogenic conversion is exploited by several pathogenic fungi and is required for tissue invasion and/or survival in the host. We have identified a homolog of a master regulator of this morphological switch in the plant pathogenic fungus Fusarium oxysporum f. sp. lycopersici. This non-dimorphic fungus causes vascular wilt disease in tomato by penetrating the plant roots and colonizing the vascular tissue. Gene knock-out and complementation studies established that the gene for this putative regulator, SGE1 (SIX Gene Expression 1), is essential for pathogenicity. In addition, microscopic analysis using fluorescent proteins revealed that Sge1 is localized in the nucleus, is not required for root colonization and penetration, but is required for parasitic growth. Furthermore, Sge1 is required for expression of genes encoding effectors that are secreted during infection. We propose that Sge1 is required in F. oxysporum and other non-dimorphic (plant) pathogenic fungi for parasitic growth

CELLULOSE-TRIGGERED SPORULATION IN THE GALACTOSE OXIDASE-PRODUCING FUNGUS CLADOBOTRYUM (DACTYLIUM) DENDROIDES NRRL-2903 AND ITS REIDENTIFICATION AS A SPECIES OF FUSARIUM

The production of extracellular galactose oxidase is limited to a few fungal species, including the important plant pathogens Fusarium graminearum and F. moniliforme. The best-studied enzyme is the one produced by the mycoparasitic fungus Cladobotryum (Dactylium) dendroides NRRL 2903. The NRRL 2903 strain was first mis-identified as Polyporus circinatus and later re-determined as Dactylium dendroides, although sporulation was never observed and the fungus was regarded as sterile. Upon growth at 25-degrees-C, 50 rpm, in liquid medium containing 2% cellulose as the sole carbon source, and in the presence of 0.5-0.75% yeast extract, conidial production was induced in NRRL 2903, which was re-identified as Fusarium sp. The only other known commercial strain of Cladobotryum (Dactylium) dendroides able to produce galactose oxidase, ATCC 46032, also produced fusiform conidia upon growth in cellulose-containing medium, and was shown to be genetically identical to the NRRL 2903 strain. Genetic comparison with six different representative strains of Cladobotryum dendroides (teleomorph: Hypomyces rosellus), and four strains of the closely related Hypomyces aurantius, based on the analysis of the presence or absence of a homologous galactose oxidase gene (gaoA), RAPD-PCR and RFLP analysis, confirm the distinct nature of the NRRL 2903 strain and Cladobotryum dendroides. Despite the resemblance of NRRL 2903 conidia and conidiophores to those of Fusarium chlamydosporum genetic comparison, with three different strains, suggests NRRL 2903 cannot be re-identified as F. chlamydosporum. Two of the strains, however, contain a region in their genome that is highly homologous to the galactose oxidase gene (gaoA), and one strain exhibits extracellular galactose oxidase activity but only partial homology to the gaoA gene of NRRL 2903