δ-Aminolaevulinic acid synthesis is required for virulence of the wheat pathogen Stagonospora nodorum

Abstract

d-Aminolaevulinic acid (ALA) is synthesized in fungi by ALA synthase, a key enzyme in the synthesis of haem. The requirement for ALA synthase in Stagonospora nodorum to cause disease in wheat was investigated. The single gene encoding ALA synthase (Als1) was cloned and characterized. Expression analysis determined that Als1 transcription was up-regulated during germination and also towards the latter stages of the infection. The Als1 gene was further characterized by homologous gene replacement. The inactivation of Als1 resulted in strains producing severely stunted germ tubes leading quickly to death. The strains could be recovered by supplementation with 33 mM ALA. Pathogenicity assays revealed the als1 strains were essentially non-pathogenic, inferring a key role for the synthesis of ALA during in planta growth. Supplementing the strains with ALA restored growth in vitro and also pathogenicity for up to 5 days after inoculation. Further examination by inoculating the als1 strains onto wounded leaves found that pathogenicity was only partially restored, suggesting that host-derived in planta levels of ALA are not sufficient to support growth. This study has identified a key role for fungal ALA synthesis during infection and revealed its potential as an antifungal target.

Ferrochelatase is a conserved downstream target of the blue light-sensing White collar complex in fungi

“…It may be that either normal levels of haem are required for pathogenesis or the strains are less fit due to changes in regulation, since HEM15 is essential. Haem biosynthesis is required for virulence in both plant and animal pathogenic fungi (Kirsch & Whitney, 1991; Solomon et al , 2006). The hemH gene encoding ferrochelatase of the α -proteobacterium Brucella abortus is required for virulence (Almirón et al , 2001).…”

Genetic linkage map of Phaeosphaeria nodorum, the causal agent of stagonospora nodorum blotch disease of wheat

“…From these, two sets of primer pairs were selected for each of nine genes, and one primer set was selected for Hdh2. In addition, the gene sequences encoding MAP kinase (Mak2), trifunctional histidine biosynthesis (his) and β-tubulin (tubA) were analysed in two parental isolates Solomon et al 2006;Wang et al 2007). No nucleotide variation was identified in these three genes.…”

“…Several genes involved in P. nodorum pathogenicity and sporulation, such as those encoding malate synthase, ornithine decarboxylase, mitogen-activated protein kinase, Gα protein subunit, δ-amino laevulinic acid synthase, and mannitol 1-phosphate dehydrogenase have been identified (Bailey et al 2000;Solomon et al 2006Solomon et al 2004aSolomon et al , b, 2005a. A draft genome sequence of P. nodorum strain SN15 comprising 37.2 mega base pairs (Mbp) of nuclear DNA in 107 scaffolds and containing an estimated minimum of 10,762 genes was reported (Hane et al 2007).…”

RNA interference pathways in filamentous fungi

“…A co-suppression phenomenon like that in plants was observed in Cladosporium fulvum in 1998 [83,117] and a homology-dependent silencing was observed in Schizophyllum commune in 1997 [118]. Since the seminal report of RNAi in 1998 [7], gene expression suppression by utilizing a dsRNA-expressing system has been found and successfully applied in many pathogenic and non-pathogenic fungi including Ascomycota , Basidiomycota , and Zygomycota , such as Magnaporthe oryzae [119], Sclerotinia sclerotiorum [120], Aspergillus fumigatus [121-124], Aspergillus oryzae [119,125], Aspergillus flavus [126] and Aspergillus parasiticus [126], Bipolaris oryzae [127], Colletotrichum lagenarium [128], Colletotrichum gloeosporioides [129], Coprinus cinereus [130-131], Fusarium solani [132], Fusarium graminearum [126], Fusarium verticillioides [133], Mucor circinelloides [115-116], Moniliophthora perniciosa [134], Histoplasma capsulatum [135-136], Cryptococcus neoformans [137], Schizophyllum commune [118,138], Coniothyrium minitans [139], Stagonospora nodorum [140], Ophiostoma floccosum and O. piceae [141], Botrytis cinerea [142] and so on, with some of them showing the involvement of dicer in the silencing and siRNA production, suggesting RNA silencing is conserved in most of fungal species [83,143]. …”