A fungal gene for antibiotic resistance on a dispensable (“B”) chromosome

Department of Plant Pathology, Cornell University, Ithaca, NY 14853.
Science (Impact Factor: 31.48). 01/1992; 254(5039):1773-6. DOI: 10.1126/science.1763326
Source: PubMed

ABSTRACT A family of cytochrome P-450 (Pda) genes in the pathogenic fungus Nectria haematococca is responsible for the detoxification of the phytoalexin pisatin, an antimicrobial compound produced by garden pea (Pisum sativum L.). The Pda6 gene was mapped by electrophoretic karyotype analysis to a small meiotically unstable chromosome that is dispensable for normal growth. Such traits are typical of B chromosomes. The strains of Nectria studied here have no sequences that are homologous to the Pda family other than Pda6 and therefore demonstrate that unique, functional genes can be found on B chromosomes. Unstable B chromosomes may be one mechanism for generating pathogenic variation in fungi.

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    • "Our data leave open the question of the relevance of ACs for infectivity in particular. Determinants of host specificity and virulence have been identified on ACs of other fungal plant pathogens, including the AC-encoded enzymes for detoxification of a plant phytoalexin in Nectria haematococca (Miao et al. 1991; Coleman et al. 2011) and the virulence-associated host-specific effector genes on lineage-specific chromosomes of Fusarium oxysporum (Ma et al. 2010). Though we detected no host-specific gene expression of AC genes at the very early stages of infection, 25 AC-encoded genes were upregulated during infection of wheat at 13 dpi (Yang et al. 2013). "
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    ABSTRACT: Host specialization by pathogens requires a repertoire of virulence factors as well as fine-tuned regulation of gene expression. The fungal wheat pathogen Zymoseptoria tritici (synonym Mycosphaerella graminicola) is a powerful model system for the discovery of genetic elements that underlie virulence and host specialization. We transcriptionally profiled the early stages of Z. tritici infection of a compatible host (wheat) and a noncompatible host (Brachypodium distachyon). The results revealed infection regulatory programs common to both hosts and genes with striking wheat-specific expression, with many of the latter showing sequence signatures of positive selection along the Z. tritici lineage. Genes specifically regulated during infection of wheat populated two large clusters of coregulated genes that may represent candidate pathogenicity islands. On evolutionarily labile, repeat-rich accessory chromosomes (ACs), we identified hundreds of highly expressed genes with signatures of evolutionary constraint and putative biological function. Phylogenetic analyses suggested that gene duplication events on these ACs were rare and largely preceded the diversification of Zymoseptoria species. Together, our data highlight the likely relevance for fungal growth and virulence of hundreds of Z. tritici genes, deepening the annotation and functional inference of the genes of this model pathogen.
    Genome Biology and Evolution 06/2014; 6(6). DOI:10.1093/gbe/evu101 · 4.53 Impact Factor
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    • "There is no evidence in the literature that the minichromosome plays a role in pathogenicity or virulence of L. maculans, as has been reported for the minichromosome of Nectria haematococca Berk. & Broome, which codes for an enzyme that detoxifies the phytoalexin pisatin (Miao et al. 1991). Leclair et al. (1996) reported no significant difference in the pathogenicity and host range of PG3 isolates (aggressive) possessing or not possessing a minichromosome. "
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    ABSTRACT: Black leg of crucifers, caused by Leptosphaeria maculans (Desm.) Ces. and de Not., is the most important disease of broccoli and cauliflower in central Mexico, causing up to 70% yield loss in cauliflower crops. Isolates recovered from broccoli crops at Aguascalientes and Zacatecas, central Mexico, had the morphological characteristics of the aggressive strain of the fungus. Most of the isolates were pathogenic to cauliflower and canola, but two isolates had a low aggressivity on these hosts. Electrophoretic karyotypes of the Mexican isolates were generated by contour-clamped homogeneous electric field gel electrophoresis. The karyotypes were characteristic of isolates belonging to the aggressive strain ofL. maculans, with 9–12 chromosomes distributed in three size ranges, namely 2.3–1.9, 1.6–1.2, and 0.9–0.8 (minichromosome) megabases. Overall, minimum genome size ranged from 16.1 to 23.0 megabases. We have shown that the LMR1 repetitive element, which is specific to aggressive isolates ofL. maculans, was present in all the Mexican isolates, including the two isolates with low aggressivity on cauliflower and canola, confirming that these belong to the aggressive strain of the fungus.
    Canadian Journal of Plant Pathology 07/2012; March 2002(1-Vol. 24):69-73. DOI:10.1080/07060660109506974 · 0.99 Impact Factor
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    • "Two findings from subsequent studies helped diffuse this apparent confusion. Firstly, it was found that the PDA1 gene is located on a 1.6 million base pair (Mb) conditional dispensable chromosome (Miao et al., 1991b; Wasmann and VanEtten, 1996), and secondly, it was also observed that additional gene(s) located on the same dispensable chromosome is/are required for high virulence on peas (Wasmann and VanEtten, 1996). This dispensable chromosome is reported to possess six genes: PDA1, PEP1, PEP2, PEP3, PEP4 and PEP5 (Fig. 4), all clustered together (Liu et al., 2003; Temporini and VanEtten, 2002). "
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    ABSTRACT: Footrot disease due to N. haematococca (anamorph Fusarium solani f. sp. pisi) is a globally, economically important disease of peas. The disease has been linked to the presence of six pea pathogenicity (PEP) genes (PDA1, PEP1, PEP2, PEP3, PEP4 and PEP5) inherent in pathogenic forms of the causal fungus N. haematococca MPIV. The disease is prevented only through avoidance of fields with high disease potential. Identifying agricultural fields with a high disease potential prior to pea cultivation has been paramount in the implementation of preventive measures. Although molecular techniques have been successfully used to quantify pathogenic strains of N. haematococca in agricultural soils, targeting all six pathogenicity genes in these assays would not be cost effective. This study therefore attempts to review the functions and roles of the different genes linked with pea pathogenicity with the aim of identifying gene(s) that would serve as a logical target in a quantitative molecular assay. Findings suggest that, whilst the PDA gene may be targeted in a preliminary diagnostic measure, a conclusive assay, targeting the PEP3 gene may be required to affirm pea footrot disease potential of agricultural fields. Agricultural fields with the PEP3 gene copy numbers of up to 100 per g soil prior to cultivation may be deemed unsafe for peas.
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