Donald L. Nuss

Bio: Donald L. Nuss is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Hypovirus & Chestnut blight. The author has an hindex of 44, co-authored 80 publications receiving 5446 citations. Previous affiliations of Donald L. Nuss include Hoffmann-La Roche & University of Maryland Biotechnology Institute.

Hypovirulence: Mycoviruses at the fungal–plant interface

Abstract: Whereas most mycoviruses lead 'secret lives', some reduce the ability of their fungal hosts to cause disease in plants. This property, known as hypovirulence, has attracted attention owing to the importance of fungal diseases in agriculture and the limited strategies that are available for the control of these diseases. Using one pathogen to control another is appealing, both intellectually and ecologically. The recent development of an infectious cDNA-based reverse genetics system for members of the Hypoviridae mycovirus family has enabled the analysis of basic aspects of this fascinating virus–fungus–plant interaction, including virus–host interactions, the mechanisms underlying fungal pathogenesis, fungal signalling pathways and the evolution of RNA silencing. Such systems also provide a means for engineering mycoviruses for enhanced biocontrol potential.

Evidence that RNA silencing functions as an antiviral defense mechanism in fungi

Abstract: The role of RNA silencing as an antiviral defense mechanism in fungi was examined by testing the effect of dicer gene disruptions on mycovirus infection of the chestnut blight fungus Cryphonectria parasitica. C. parasitica dicer-like genes dcl-1 and dcl-2 were cloned and shown to share a high level of predicted amino acid sequence identity with the corresponding dicer-like genes from Neurospora crassa [Ncdcl-1 (50.5%); Ncdcl-2 (38.0%)] and Magnaporthe oryzae [MDL-1 (45.6%); MDL-2 (38.0%)], respectively. Disruption of dcl-1 and dcl-2 resulted in no observable phenotypic changes relative to wild-type C. parasitica. Infection of Δdcl-1 strains with hypovirus CHV1-EP713 or reovirus MyRV1-Cp9B21 resulted in phenotypic changes that were indistinguishable from that exhibited by wild-type strain C. parasitica EP155 infected with these same viruses. In stark contrast, the Δdcl-2 and Δdcl-1/Δdcl-2 mutant strains were highly susceptible to mycovirus infection, with CHV1-EP713-infected mutant strains becoming severely debilitated. Increased viral RNA levels were observed in the Δdcl-2 mutant strains for a hypovirus CHV1-EP713 mutant lacking the suppressor of RNA silencing p29 and for wild-type reovirus MyRV1-Cp9B21. Complementation of the Δdcl-2 strain with the wild-type dcl-2 gene resulted in reversion to the wild-type response to virus infection. These results provide direct evidence that a fungal dicer-like gene functions to regulate virus infection.

Hypoviruses and Chestnut Blight: Exploiting Viruses to Understand and Modulate Fungal Pathogenesis

Abstract: Fungal viruses are considered unconventional because they lack an extracellular route of infection and persistently infect their hosts, often in the absence of apparent symptoms. Because mycoviruses are limited to intracellular modes of transmission, they can be considered as intrinsic fungal genetic elements. Such long-term genetic interactions, even involving apparently asymptomatic mycoviruses, are likely to have an impact on fungal ecology and evolution. One of the clearest examples supporting this view is the phenomenon of hypovirulence (virulence attenuation) observed for strains of the chestnut blight fungus, Cryphonectria parasitica, harboring members of the virus family Hypoviridae. The goal of this chapter is to document recent advances in hypovirus molecular genetics and to provide examples of how that progress is leading to the identification of virus-encoded determinants responsible for altering fungal host phenotype, insights into essential and dispensable elements of hypovirus replication, revelations concerning the role of G-protein signaling in fungal pathogenesis, and new avenues for enhancing biological control potential.

Distinct roles for two G protein α subunits in fungal virulence, morphology, and reproduction revealed by targeted gene disruption

Abstract: Reduced accumulation of the GTP-binding protein G(i)alpha subunit CPG-1, due either to hypovirus infection or transgenic cosuppression, correlates with virulence attenuation of the chestnut blight fungus, Cryphonectria parasitica. The role of G protein-mediated signal transduction in fungal virulence was further examined by targeted disruption of the gene cpg-1, encoding CPG-1, and a second Galpha gene, cpg-2, encoding the subunit CPG-2. Disruption of cpg-1 resulted in a set of phenotypic changes similar to, but more severe than, those associated with hypovirus infection. Changes included a marked reduction in fungal growth rate and loss of virulence, asexual sporulation, female fertility, and transcriptional induction of the gene lac-1, encoding the enzyme laccase. In contrast, cpg-2 disruption resulted in only slight reductions in growth rate and asexual sporulation and no significant reduction in virulence, female fertility, or lac-1 mRNA inducibility. These results provide definitive confirmation of previous correlative evidence that suggested a requirement of CPG-1-linked signaling for a number of fungal processes, including virulence and reproduction, while demonstrating that a second Galpha, CPG-2, is dispensable for these processes. They also significantly strengthen support for the apparent linkage between hypovirus-mediated disruption of G protein signal transduction and attenuation of fungal virulence.

Trichoderma species--opportunistic, avirulent plant symbionts.

Abstract: Trichoderma spp. are free-living fungi that are common in soil and root ecosystems. Recent discoveries show that they are opportunistic, avirulent plant symbionts, as well as being parasites of other fungi. At least some strains establish robust and long-lasting colonizations of root surfaces and penetrate into the epidermis and a few cells below this level. They produce or release a variety of compounds that induce localized or systemic resistance responses, and this explains their lack of pathogenicity to plants. These root-microorganism associations cause substantial changes to the plant proteome and metabolism. Plants are protected from numerous classes of plant pathogen by responses that are similar to systemic acquired resistance and rhizobacteria-induced systemic resistance. Root colonization by Trichoderma spp. also frequently enhances root growth and development, crop productivity, resistance to abiotic stresses and the uptake and use of nutrients.

A unified classification system for eukaryotic transposable elements

Abstract: Our knowledge of the structure and composition of genomes is rapidly progressing in pace with their sequencing. The emerging data show that a significant portion of eukaryotic genomes is composed of transposable elements (TEs). Given the abundance and diversity of TEs and the speed at which large quantities of sequence data are emerging, identification and annotation of TEs presents a significant challenge. Here we propose the first unified hierarchical classification system, designed on the basis of the transposition mechanism, sequence similarities and structural relationships, that can be easily applied by non-experts. The system and nomenclature is kept up to date at the WikiPoson web site.

Fungal secondary metabolism — from biochemistry to genomics

Abstract: Much of natural product chemistry concerns a group of compounds known as secondary metabolites. These low-molecular-weight metabolites often have potent physiological activities. Digitalis, morphine and quinine are plant secondary metabolites, whereas penicillin, cephalosporin, ergotrate and the statins are equally well known fungal secondary metabolites. Although chemically diverse, all secondary metabolites are produced by a few common biosynthetic pathways, often in conjunction with morphological development. Recent advances in molecular biology, bioinformatics and comparative genomics have revealed that the genes encoding specific fungal secondary metabolites are clustered and often located near telomeres. In this review, we address some important questions, including which evolutionary pressures led to gene clustering, why closely related species produce different profiles of secondary metabolites, and whether fungal genomics will accelerate the discovery of new pharmacologically active natural products.