Progress 10/01/03 to 09/30/04
Outputs
Fungi attack all living organisms and are the major class of plant pathogens. Despite existing control measures, fungal infections are common and crop yields are often poor. Environmental concerns and cost will prevent more extensive use of existing chemical fungicides. Improved understanding of the mechanism(s) of fungal infection is necessary to either refine current control measures or develop new strategies. Methods are now available to study the molecular details of fungal infection. However, the molecular mechanisms underlying fungal pathogenicity are not well understood. This project will continue efforts designed to advance our understanding of pathogenic development signal transduction and host plant resistance in two fungal-plant interactions; Colletotrichum trifolii/alfalfa and Sclerotinia sclerotiorum/dicotyledonous plants. Understanding the molecular bases of disease development will facilitate the development of rational, durable and environmentally
Impacts
Understanding the relevant signaling pathways in plant pathogenic fungi will permit the design of alternative and potentially effective didease control strategies.
Publications
- Chen, C., and Dickman, M.B. 2004. Dominant active Rac and dominant negative Rac revert the dominant active Ras phenotype in Colletotrichum trifolii by distinct signaling pathways. Mol. Microbiol. 51: 1493-1507.
- Chen, C., Harel, A., Gorovits, R., Yarden, O., and Dickman, M.B. 2004. Regulation of sclerotial development in Sclerotinia sclerotiorum is linked with pH and cAMP sensing. Mol. Plant Microbe Interact. 17: 404-413.
- Jurick, W., Dickman, M.B., and Rollins , J.A. 2004. Characterization and functional analysis of a cAMP-dependent protein kinase A catalytic subunit gene (pka1) in Sclerotinia sclerotiorum. Physiol. Mol. Plant Pathol. (In press).
- Chen, C. and Dickman, M.B. 2004. cAMP blocks MAPK activation and sclerotial development via Rap-1 in a PKA-independent manner in Sclerotinia sclerotiorum. Mol. Micrbiol. (in press).
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Progress 10/01/02 to 09/30/03
Outputs
The small G-protein superfamily is an evolutionarily conserved group of GTPases that regulate diverse signaling pathways including pathways for growth and development in eukaryotes. Previously, we showed that dominant active mutation in the unique Ras gene (Ct-RasVal2) of the fungal phytopathogen Colletotrichum trifolii displays a nutrient-dependent phenotype affecting polarity, growth and differentiation. Signaling via the MAP kinase pathway is significantly impaired in this mutant as well. These findings suggest that Ras-mediated ROS generation is dependent on a Rac-cPLA2-linked signaling pathway. Taken together, this study provides evidence that Rac functions to restore the hyphal morphology of Ct-RasVal2 by regulating MAPK activation and intracellular ROS generation.
Impacts
Understanding the relevant signaling pathways in plant pathogenic fungi will permit the design of alternative and potentially effective didease control strategies.
Publications
- Ahmed ,A.,Cohen-Gould, S., Ha, Y.S. , Crawford , T., Dickman, M. B. and Dussault, P.H. 2003. Synthesis of (R) and (S) 10,16-Dihydroxyhexadecanoate: Assignment of cutin stereochemistry and relative activation of fungal pathogens. Phytochemistry 63: 47-52.
- Dickman, M.B. Ha, Y.S.,Yang, Z., Adams, B., and Huang, C. 2003. A protein kinase from Colletotrichum trifolii is induced by plant cutin and is required for appressorium formation. Mol. Plant-Microbe Inter. 16:411-421.
- Yarden, O., Ebbole, D.J., Freeman, S.,.Rodriguez, R.J., and Dickman, M.B. 2003. Fungal Biology and Agriculture: Revisiting the Field. Mol. Plant Mictrobe Interact. 16: 859-866
- Ha, Y.S., Memmott, SD., and Dickman, M.B. 2003. Functional analysis of Ras in Colletotrichum trifolii. FEMS Lett. 226:315-321.
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Progress 10/01/01 to 09/30/02
Outputs
Sclerotinia sclerotiorum is an extremely broad host range, necrotrophic fungal plant pathogen. Effective pathogenesis by this fungus requires the secretion of oxalic acid (OA), a primary pathogenicity determinant. Studies are being conducted to determine the mode of action of OA. Results have indicated that OA modulates the ambient pH by acidification, which serves as a regulatory cue for processes linked to pathogenicity and development including the activation of a OA induced MAPK that is required for sclerotial development. In addition, our studies have shown that oxalate suppresses the oxidative burst of a number of host plants. Oxalate defective mutants are non-pathogenic and do not alter the plant oxidative burst. Colletotrichum trifolii is the causal agent of alfalfa anthracnose. We have cloned and characterized a number of genes involved in prepenetration development, including the small prototypical G proteins,RAS, RAC, and CDC42.Transformants expressing
constitutively active forms of Ras and CDC42 have nutritional dependent phenotypes. On minimal medium, transformants lose polarity have distended hyphae and fail to differentiate, while on rich media, these transformants are indistinguishable from wild type. Peptone reverts the phenotype observed on minimal medium and more specifically proline alone also reverses this phenotype in both sets of mutants.Dickman, M.B., Ha, Y.S., Yang, Z., Adams, B. and Huang, C. 2002. A protein kinase from Colletotrichum trifolii is induced by plant cutting and is required for appressorium development. Mol. Plant Microbe Inter. (In review). Dickman, M.B., Ha, Y.S., Yang, Z., Adams, B. and Huang, C. 2002. A protein kinase from Colletotrichum trifolii is induced by plant cutting and is required for appressorium development. Mol. Plant Microbe Inter. (In review).
Impacts
A better understanding of pathogenicity in Colletotrichum species and Sclerotinia sclerotiorum and the response of plants to these pathogens is critical to the development of effective and long term plant disease control measures.
Publications
- Chen, C. and Dickman, M.B. 2002. Colletotrichum trifolii TBB lcinase, a COTI homolog, is light inducible and becomes localized in the nucleus during hyphal elongation. Eukaryotic Cell. 1:626-633.
- Memmott, S.D., Ha, Y-S., and Dickman, M.B. 2002. Proline reverses the abnormal phenotypes of Colletotrichum trifolii associated with expression of endogenous constitutively active Ras. Appl. Env. Microbiol. 68: 1647-1651.
- Dickman, M.B., Ha, Y.S., Yang, Z., Adams, B. and Huang, C. 2002. A protein kinase from Colletotrichum trifolii is induced by plant cutting and is required for appressorium development. Mol. Plant Microbe Inter. (In review).
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Progress 10/01/00 to 09/30/01
Outputs
As part of our continuing efforts to understand sclerotial development, oxalic acid production and regulation of pathogenicity in S. sclerotiorum, we have established that pH and signals transduced via pH changes are important for these processes. Sclerotinia sclerotiorum acidifies its ambient environment by producing oxalic acid. This production of oxalic acid during plant infection has been implicated as a primary determinant of pathogenicity in this and other phytopathogenic fungi. We found that ambient pH conditions affect multiple process in S. sclerotiorum. Exposure to increasing alkaline ambient pH increased the oxalic acid accumulation independent of carbon source, sclerotial development was favored by acidic ambient pH conditions but inhibited by neutral ambient pH, and transcripts encoding the endopolygalacturonase gene pg1 accumulated maximally under acidic culture conditions. We cloned a putative transcription factor-encoding gene, pac1, that may
participate in a molecular signaling pathway for regulating gene expression in response to ambient pH. The three zinc finger domains of the predicted Pac1 protein are similar in sequence and organization to the zinc finger domains of the A. nidulans pH-responsive transcription facto PacC. The promoter of pac1 contains eight PacC consensus binding sites, suggesting that this gene, like its homologs, is autoregulated. Consistent with this suggestion, the accumulation of pac1 transcripts paralleled increase in ambient pH. Pac1 was determined to be a functional homolog of PacC by complementation of an A. nidulans pacC-null strain with pac1. Our results suggest that ambient pH is a regulatory cue for processes linked to pathogenicity, development, and virulence and that these processes may be under the molecular regulation of a conserved pH-dependent signaling pathway analogous to that in the nonpathogenic fungus A. nidulans
Impacts
A better understanding of pathogenicity in Colletotrichum species and Sclerotinia sclerotiorum and the response of plants to these pathogens is critical to the development of effective and long term plant disease control measures.
Publications
- Truesdell, G.M., Yang, Z., and Dickman, M.B. 2000. A G alpha subunit from the phytopathogenic fungus Colletotrichum trifolii is required for conidial germination. Physiological and Molecular Plant Pathology 56:131-140. Warwar, V. and Dickman, M. B. 2000. Antisense expression of the calmodulin gene from Colletotrichum trifolii impairs prepenetration development. FEMS Microbiology Letters 191: 213-219.
- Cessna, S.G., Sears, V.E., Dickman, M.B. and Low, P.S. 2000. Oxalic acid, a pathogenicity factor for Sclerotinia sclerotiorum, suppresses the host plant oxidative burst. The Plant Cell 12:2191-2199.
- Rollins, J.A. and Dickman, M.B. 2001. pH signaling in Sclerotinia sclerotiorum: Identification of a pacC/RIM1 homolog. Appl. Env. Microbiol. 67: 75-81
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Progress 10/01/98 to 09/30/99
Outputs
We have isolated a number of genes involved in prepenetration morphogenesis in Colletotrichum trifolii
Impacts
Fungal diseases of plants are of great econmic importance
Publications
- Dickman, M.B. and Yarden, O. 1999. Serine-theonine kinases and phosphatases in filamentous fungi. Fungal Genetics and Biology 26:88-117
- Yang, Z. and Dickman, M.B. 1999 Molecular cloning and characterization of Ct-PKAR, a gene encoding thr regulatory subunit of cAMP-dependent protein kinase in Colletotrichum trifolii. Archives of Microbiology 171:249-256.
- Truesdell, G.M., Jones, C., Holt, T., Henderson, G., and Dickman,M.B. 1999. Defects in hyphal growth polarity and and mammalian tumors induced by Ras from a phytpathogenic fungus. Mol. Gen. Genet. 262: 46-54.
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