The Sfp-Type 4′-Phosphopantetheinyl Transferase Ppt1 of Fusarium fujikuroi Controls Development, Secondary Metabolism and Pathogenicity

Abstract

The heterothallic ascomycete Fusarium fujikuroi is a notorious rice pathogen causing super-elongation of plants due to the production of terpene-derived gibberellic acids (GAs) that function as natural plant hormones. Additionally, F. fujikuroi is able to produce a variety of polyketide- and non-ribosomal peptide-derived metabolites such as bikaverins, fusarubins and fusarins as well as metabolites from yet unidentified biosynthetic pathways, e.g. moniliformin. The key enzymes needed for their production belong to the family of polyketide synthases (PKSs) and non-ribosomal peptide synthases (NRPSs) that are generally known to be post-translationally modified by a Sfp-type 4′phosphopantetheinyl transferase (PPTase). In this study we provide evidence that the F. fujikuroi Sfp-type PPTase FfPpt1 is essentially involved in lysine biosynthesis and production of bikaverins, fusarubins and fusarins, but not moniliformin as shown by analytical methods. Concomitantly, targeted Ffppt1 deletion mutants reveal an enhancement of terpene-derived metabolites like GAs and volatile substances such as α-acorenol. Pathogenicity assays on rice roots using fluorescent labeled wild-type and Ffppt1 mutant strains indicate that lysine biosynthesis and iron acquisition but not PKS and NRPS metabolism is essential for establishment of primary infections of F. fujikuroi. Additionally, FfPpt1 is involved in conidiation and sexual mating recognition possibly by activating PKS- and/or NRPS-derived metabolites that could act as diffusible signals. Furthermore, the effect on iron acquisition of Ffppt1 mutants led us to identify a previously uncharacterized putative third reductive iron uptake system (FfFtr3/FfFet3) that is closely related to the FtrA/FetC system of A. fumigatus. Functional characterization provides evidence that both proteins are involved in iron acquisition and are liable to transcriptional repression of the homolog of the Aspergillus GATA-type transcription factor SreA under iron-replete conditions. Targeted deletion of the first Fusarium homolog of this GATA-type transcription factor-encoding gene, Ffsre1, strongly indicates its involvement in regulation of iron homeostasis and oxidative stress resistance.

Two Histone Deacetylases, FfHda1 and FfHda2, Are Important for Fusarium fujikuroi Secondary Metabolism and Virulence

“…Microscopic analyses of a gibberellindeficient strain showed significantly fewer penetration events of the root cells within the rice plants than the wild type (17). Similarly, deletion of ppt1 in F. fujikuroi, which resulted in the complete loss of polyketide synthase (PKS)-and NRPS-derived products, had no impact on rice root penetration (60). Once penetration occurs, minor amounts of gibberellins are likely enough to induce bakanae symptoms.…”

“…For gibberellin analysis, 20 ml of culture fluid of 7-day-old cultures was extracted over a C 18 cartridge and measured by using high-performance liquid chromatography coupled to UV detection (HPLC-UV) as described previously (60). For analysis of bikaverin, fusarubins, fusarins, and fusaric acid, culture fluid of 7-day-old cultures was filtered over a 0.2-m membrane filter (Millex; Millipore) and used directly for analysis without further preparation, as described previously (29).…”

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…Colony cross-feeding experiments showed that GmcA is necessary for the synthesis of a metabolite that can be transmitted extracellularly (289), different from the sporulation signals produced through the FluG and the AfeA-TmpA pathways (279,280). The regulation of conidiation by secondary-metabolism-derived signals is conserved in other fungi, such as Fusarium fujikuroi (290). Nevertheless, the mechanisms by which all these signals regulate conidiation are unknown.…”

A RALDH-like enzyme involved in Fusarium verticillioides development

“…In the heterothallic species F. fujikuroi, mutants of the G subunit gene ffg1 do not develop perithecia in the MAT1-1 mating background (Studt et al, 2013) and mutants of the Sfp-type phosphopantetheinyl transferase gene ppt1 do not develop perithecia in a MAT1-2 mating background (Wiemann et al, 2012). The ΔcarY phenotype resembles the mutation in the precursor and pheromone receptor genes in that it reduces but it does not totally abolish the formation of perithecia.…”