Dothistromin toxin is a virulence factor in dothistroma needle blight of pines

Abstract

Dothistromin is a broad-spectrum mycotoxin produced by the Dothideomycete pine needle pathogen Dothistroma septosporum. It accumulates in lesions, causing characteristic red bands on needles infected with this fungus. Dothistromin is similar in structure to the aflatoxin precursor versicolorin B and the biosynthetic pathways of these toxins share many common gene products. Although dothistromin is not essential for pathogenicity in dothistroma needle blight, its presence in infected needles suggests it might have a role in the disease process. The hypothesis that dothistromin is a virulence factor was tested by studying Pinus radiata infected with dothistromin-deficient mutants of D. septosporum. The mutants were able to infect pine needles and complete their life cycle as previously shown, and were unaffected in spore germination, epiphytic growth or needle penetration. However, colonization of the mesophyll by the mutants was restricted compared to the wild type. Correspondingly, lesions produced by the mutants were smaller and produced significantly fewer spores than lesions produced by wildtype strains. Interestingly, 'green islands', in which chlorophyll was maintained at a higher level than in adjacent chlorotic and necrotic regions, surrounded early-appearing lesions caused by both wildtype and mutant strains. At a later stage of disease development green islands were still present in the mutant but appeared to be masked by the extended dothistromin-containing lesions in the wild type. Overall the results support a role for dothistromin in virulence in dothistroma needle blight.

A worldwide perspective on the management and control of Dothistroma needle blight

“…Furthermore, in those regions where only one mating type is (Eschen et al 2015). These risks are being assessed using increasingly sophisticated molecular techniques which help researchers gain a better understanding of both the population biology and the molecular basis of virulence in D. septosporum (Barnes et al 2014;Bradshaw et al 2015;Kabir et al 2015).…”

“…As reviewed by Fraser et al (2016c), the mechanisms of resistance to DNB are complex, not well understood and are also influenced by other heritable traits and external abiotic and biotic factors. The genome sequence of D. septosporum revealed the presence of effectors that are recognised by immune receptors from tomato (De Wit et al 2012) and this fuelled current research on molecular host-pathogen interactions in the Dothistroma-Pinus pathosystem (Bradshaw et al 2015). However, genomic studies of the Pinaceae hosts are in their infancy due to their immense size, with the first pine genome only recently published (Zimin et al 2014).…”

Regulation of the aflatoxin-like toxin dothistromin by AflJ

“…The forest pathogen Dothistroma septosporum also has an AflJ-like gene (DsAflJ ) thought to be associated with biosynthesis of the virulence factor dothistromin, a chemical relative of aflatoxin (Fig 1) Kabir et al 2014). Dothistromin biosynthetic genes are arranged at six separate loci on a 1.3-Mb chromosome ) rather than being clustered as in aflatoxin biosynthesis (Keller & Hohn 1997).…”

A review of Pinaceae resistance mechanisms against needle and shoot pathogens with a focus on the Dothistroma–Pinus interaction

“…However, dothistromin production is not required for infection of P. radiata, as genetically modified D. septosporum strains, unable to produce the toxin, are still able to complete their life cycle on this host (Schwelm et al 2009). Recent research has shown that dothistromin production is a virulence factor that is required for expansion of the necrotic lesions and for normal levels of conidia production on P. radiata (Kabir et al 2015).…”

“…release the mycotoxin dothistromin (Bassett et al 1970), which is closely related to the aflatoxin precursor, versicolorin B (Chettri et al 2013). Dothistromin release leads to disruption of mesophyll tissue in advance of growing Dothistroma hyphae (Gadgil 1967;Kabir et al 2015) and is responsible for the red colour seen on symptomatic needles (Shain and Franich 1981). Dothistromin injection can also generate a hypersensitive-like response in P. radiata needles, the plant producing benzoic acid as a phytoalexin and highly lignified lesiondelineating bands (Franich et al 1986).…”