Stachybotrys elegans is a mycoparasite of the soilborne plant pathogen fungus Rhizoctonia solani. The mycoparasitic activity of S. elegans is correlated with the production of cell wall-degrading enzymes such as chitinases. This study details the cloning and characterization of the cDNA, sechi44, that encodes an extracellular endochitinase. The expression regulation of sechi44 was altered when S. elegans was in interaction with its host, R. solani, and also when the mycoparasite was grown on minimal media amended with different carbon and nitrogen sources. Direct contact with R. solani significantly upregulated sechi44 expression which followed a cyclical pattern suggesting that this gene has a role not only in mycoparasitism, but also in linear growth of the mycoparasite. The addition of high concentrations of glucose and ammonium triggered a decrease of sechi44 expression suggesting that sechi44 is subject to glucose and ammonium repression. In a separate study, several genes (1016 clones) whose transcription was substantially up-regulated during the mycoparasitic interaction were identified using SSH and microarray analysis. Twenty-five percent (261 clones) of these were sequenced and assigned to putative functions. Among them, 15 expressed sequence tags (ESTs) were identified in R. solani whose functions were related to defense while the majority of ESTs were identified in S. elegans and assigned functions related to toxin metabolism, pathogenic process, stress response., multidrug resistance, apoptosis, transport, ATP synthesis, replication, transcription and DNA repair, translation, transduction, protein degradation, and ribosomal protein. The overexpression of 13 selected genes of S. elegans was validated and confirmed using quantitative reverse transcription polymerase chain reaction (QRT-PCR). The temporal gene expression of nine genes was monitored when the mycoparasite was grown on R. solani (host) and Sclerotinia sclerotiorum (non-host) mycelia and sclerotia. Some genes such as seglu, selec, and se151 were completely inhibited by the presence of non-host hyphae suggesting that these genes play an important role during mycoparasitism. Also, the absence of these corresponding transcripts suggests that the non-host produces transcription inhibitors. As expected, gene expression of cytochrome P450 was highly up-regulated early after germination of S. elegans conidia. This is in agreement with our finding in the EST data mining study, in which a role in toxin production was assigned to cytochrome P450.

The phototactic zoospores of Nowakowskiella elegans (Nowak.) Schroeter and Cladochytrium replicatum Karling are similar in their ultrastructure and typical of the revised Chytridiales (Barr, 1980, Can. J. Bot. 58: 2380-2394). For a carbon source both species utilize cellulose, D-cellobiose, D-glucose, D-xylose, and D-mannose. Several sources of organic nitrogen, and inorganic nitrate, and ammonium are utilized. Both species are deficient for thiamine. Germination of the zoospore cyst in both cases is exogenous, and daughter nuclei migrate and divide independently in the developing rhizomycelium. Mitosis is intranuclear. Zoospore discharge in N. elegans is operculate and vesicular, and in C. replicatum inoperculate and vesicular. Resting spores are formed asexually in C. replicatum and sexually in N. elegans. Meiosis in N. elegans is described. Nowakowskiella and Cladochytrium are retained in the family Cladochytriaceae.

Mutations in the clk-1 gene of Caenorhabditis elegans result in an average slowing down and deregulation of a variety of developmental and physiological processes. In addition, clk-1 mutants are defective in responding to temperature changes. For example, wild-type worms adjust their defecation cycle length after a temperature shift whereas the defecation cycle length of clk-1 mutants is unaffected by such a shift. To understand the basis of the clk-1 phenotype, a number of genetic screens have been carried out to isolate feature-specific suppressor mutations. dsc-3(qm179) and dsc-4(qm182) were isolated in this manner. It has previously been found that dsc-3(qm179) and dsc-4(qm182) strongly suppress the slow defecation phenotype of clk-1 mutants at 20°C, as well as after a temperature shift to 25°C. Molecular analysis of dsc-4, which encodes the microsomal triglyceride transfer protein, suggests that dsc genes affect lipid metabolism. We carried out a genetic screen for additional mutations that can suppress the slow defecation of clk-1 mutants after a temperature shift to 25°C and isolated two new suppressor mutations. Complementation tests as well as linkage analysis and mapping indicates that dsc-6(qm192) and dsc-7(qm193) define new dsc genes. We analyzed the phenotype of the new suppressor strains and have found that, like dsc-4(qm182), dsc-6(qm192) and dsc-7(qm193) can suppress a variety of clk-1 phenotypes. Based on additional phenotypic analyses of the new suppressor strains, including the determination of their sensitivity to exogenous cholesterol, we believe that, like dsc-4, dsc-6 and dsc-7 encode activities that affect lipid metabolism in worms.

The mycoparasite Stachybotrys elegans represents a potential biocontrol agent of Rhizoctonia solani, the causal organism of potato stem canker. The differential expression of two mycoparasitism-induced genes was monitored in S. elegans during interactions with its host, Rhizoctonia solani, and a non-host, Sclerotinia sclerotiorum. Using real-time reverse-transcription polymerase chain reaction (QRT-PCR), comparative analyses demonstrated that hyphal and sclerotial forms triggered different patterns of gene expression in the mycoparasite, as did the presence of the host or non-host. The calmodulin gene did not appear to be involved in conidial germination or appressoria formation of S. elegans. Potential roles of calmodulin during mycoparasitism are suggested, but further studies are required. The expression of the endochitinase-encoding gene, sechi44, was susbstantial only at later stages of interaction with living host sclerotia. Host defense mechanisms probably play a role in regulating sechi44 expression. Knowledge of the genetic mechanisms underlying this mycoparasitic relationship will further our knowledge on the potential use of S. elegans in biocontrol strategies. / Le mycoparasite Stachybotrys elegans est un agent potentiel de lutte biologiquepour le contrôle de Rhizoctonia solani, un phytopathogène causant le chancre dela tige et des stolons chez la pomme de terre (Solanum tuberosum). L'expressionde deux gènes induits pendant le mycoparasitisme a été étudiée chez S. elegans,alors que le mycoparasite était en interaction avec son hôte, R. solani, et un nonhôte,Sclerotinia sclerotiorum en utilisant la PCR quantitative en temps réel. Desanalyses comparatives ont démontré que les différentes formes d'hyphes et desc1érotes, ainsi que la présence de l'hôte ou du non-hôte, induisent différentspatrons d'expression. Le gène codant pour la calmodulin (calmodulin) ne semblepas être impliqué dans la germination des conidia ou dans la formation desappressoria chez S. elegans. Des rôles possibles de calmodulin sont suggérés,mais des études plus poussées demeurent nécessaires. L'expression du gènesechi44, codant pour une endochitinase, est importante dans des stades plusavancés du mycoparasitisme sur les sc1érotes vivants de 1 'hôte. Des mécanismesde défense de l'hôte jouent probablement un rôle important dans la régulation del'expression de sechi44. Une meilleure connaissance de la régulation génétiquelors du mycoparasitisme pourrait nous aider à évaluer le potentiel de S. elegansdans des stratégies de biocontrôle.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 118-123).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 82-87). Also available in electronic version.

Thesis (M.S.)--Missouri State University, 2008. / "May 2008." Includes bibliographical references (leaves 49-52). Also available online.

Thesis (M.A.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 98-104). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Neuroscience; migration; yeast two-hybrid; MIG-10. Includes bibliographical references (leaves 58-60).

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 61-64).