Progress 10/01/99 to 09/30/04
Outputs
In previous years, this project has focussed on the Avr1b gene from the oomycete fungus Phytophthora sojae which determines cultivar-specific avirulence. This year, the Avr1b work was transferred to the project CA-D*-PPA-6938-CG which was recently funded by USDA-NRICGP NRI Competitive Grant 2001-35319-10962. This project has instead focused on characterization of the genomes of Phytophthora sojae and the genome of the newly emerged pathogen of live oaks in California, Phytophthora ramorum. The studies are intended to lay the groundwork for draft sequencing of the entire genomes of these two species. The DNA sequence of a 60 kb region of P. sojae was completed. The results showed that P. sojae genes are arranged in tight clusters, many times overlapping. The gene clusters are separated by relatively long (10-15 kb) stretches of non-coding DNA including repetitive elements. These results suggest that assembly of random shotgun sequences of the genome should proceed
easily within gene coding regions, but may be problematic in repetitive non-coding regions. The sequence also provided essential data regarding codon preferences, consensus splice sites and transcriptional start and stop sequences. Nuclear fluorescence staining in comparison with P. sojae was used to determine that the genome size of two P. ramorum isolates was 28 Mb, substantially smaller than P. sojae. The smaller size will facilitate the sequencing of this new pathogen.
Impacts
Phytophthora species infect almost every dicotyledonous plant, from crops to forests. Decoding the genomes of Phytophthora species will provide extensive insights into the mechanisms of attack by these pathogens, and many new gene targets for new chemical and genetic control measures.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
The Avr1b gene from the oomycete fungus Phytophthora sojae determines cultivar-specific avirulence. In many races of P. sojae virulent on Rps1b and Rps1k soybeans, the Avr1b gene is present but is not transcribed. This year we have shown that a gene that we have called Avr1b-2, is responsible for this loss of transcription. Avr1b-2 encodes a trans-acting factor and is located about 100 kb from Avr1b-1, in a region we have previously sequenced. In a related project, we previously showed that high frequency mitotic gene conversion occurs in some genetic hybrids of Phytophthora sojae, resulting in high levels of genetic diversity. This year we have shown that frequency of conversion is determined by genes in one particular isolate, P7076, and we have identified a candidate DNA sequence responsible for conversion.
Impacts
Phytophthora species infect almost every dicotyledonous crop. Understanding the mechanisms by which an oomycete such as P. sojae evades or defeats host defenses, and the genetic mechanisms by which it responds to selection pressures, will facilitate the design and deployment of novel disease control measures, especially novel plant disease resistance genes.
Publications
- Tyler, B. M. 2001. Genetics and genomics of the Phytophthora-host interface. Trends in Genetics. 17(11):611-614.
- Chamnanpunt, J., Shan, W-X and Tyler, B.M. 2001. High frequency mitotic gene conversion in genetic hybrids of the oomycete Phytophthora sojae. PNAS 98(25):14530-14535.
- MacGregor, T., Bhattacharya, M., Tyler, B.M., Bhat, R., Schmitthenner, A.F. and Gijzen, M. 2002. Genetic and physical mapping of Avr1a Phytophthora sojae. Genetics. In press.
- Tyler, B.M. 2002 Molecular Basis of Recognition Between Phytophthora species and their hosts. Annual Reviews of Phytopathology 40. In press
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Progress 01/01/00 to 12/31/00
Outputs
We previously isolated a gene from the oomycete fungus Phytophthora sojae which determines cultivar-specific avirulence (Avr1b). This year we have shown that expression of the gene is induced in the plant. More importantly, we have found that in many races of P.SOJAE virulent on Rps1b and Rps1k soybeans, the Avr1b gene is present but is not transcribed. This suggests that an important mechanism by which new races arise is by transcriptional silencing of avirulence genes. In a related project, we previously showed that high frequency mitotic gene conversion occurs in some genetic hybrids of Phytophthora sojae, resulting in high levels of genetic diversity. This year we have shown that the regions of DNA affected are quire short (1 kb) and that polarity of gene conversion observed at some loci is determined in cis.
Impacts
Phytophthora species infect almost every dicotyledonous crop. Understanding the mechanisms by which an oomycete such as P. sojae evades or defeats host defenses, and the genetic mechanisms by which it responds to selection pressures, will facilitate the design and deployment of novel disease control measures, especially novel plant disease resistance genes.
Publications
- De La Serna, I., Cujec, T., Shi Y., and Tyler, B. 2000. Non coordinate regulation of 5S rRNA genes and the gene encoding the 5S rRNA-binding ribosomal protein homolog in Neurospora crassa. Mol. Gen. Genet. 263:987-994.
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Progress 01/01/99 to 12/31/99
Outputs
We have isolated a gene from the oomycete fungus Phytophthora sojae which determines cultivar-specific avirulence (Avr1b). The gene had previously been localized to a 60kb region by map-based cloning. We identified Avr1b within this region by looking for genes expressed during infection. Avr1b encodes a small secreted protein that can move systemically through the plant. This protein acts as a specific elicitor of plant defense responses in soybean cultivars containing resistance gene Rps1b. In a different project we have shown that high frequency mitotic gene conversion occurs in some genetic hybrids of Phytophthora sojae, resulting in high levels of genetic diversity.
Impacts
Phytophthora species infect almost every dicotyledonous crop. Understanding the mechanisms by which an oomycete such as P. sojae evades or defeats host defenses, and the genetic mechanisms by which it responds to selection pressures, will facilitate the design and deployment of novel disease control measures, especially novel plant disease resistance genes.
Publications
- del la Serna, I., Ng, D. and Tyler, B. M. 1999. Carbon regulation of ribosomal genes in Neurospora crassa occurs by a mechanism which does not require Cre 1, the homologue of the Aspergillus carbon catabolite repressor, CreA. Fung. Genet. Biol. 26(3), 253-269.
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Progress 01/01/98 to 12/01/98
Outputs
Genetic map-based cloning has been used to isolate two genes of the fungus PHYTOPHTHORA SOJAE which determine cultivar-specific avirulence (Avr1b and Avr1k). The locations of Avr1b and Avr1k described in the 1997 report were incorrect, due to the action of a novel mitotic recombination mechanism in the region. A much larger genetic mapping experiment has correctly localized the genes to a different 50kb region. P.SOJAE transformation experiments have begun to find the location of the genes within this region. A project to physically map all of the genes of P. SOJAE by hybridization fingerprinting has reached about one half completion. The results so far suggest that repetitive sequences are clustered in the genome, and that genes occur in regions poor in repetitive sequences. DNA sequencing of a 60kb region near Avr1b has nearly been completed, as a pilot project for sequencing the entire P. SOJAE genome. The results show that P. SOJAE genes are very tightly
clustered.
Impacts
(N/A)
Publications
- CUJEC, T. P., and TYLER, B. M. 1996. Nutritional and Growth Control of RibosomalProtein mRNA and rRNA in NEUROSPORA CRASSA. Nucl. Acids Res. 24(5), 943-950. MA0, Y., and TYLER, B. M. 1996. Cloning and Sequence Analysis of Elicitin Genes of PHYTOPHTHORA SOJAE. Fungal Genet. Biol. 20(2),169-172.
- CUJEC, T. P., and TYLER, B. M. 1996. Functional Promoter Elements Common to Ribosomal Protein and Ribosomal RNA Genes in NEUROSPORA CRASSA. Mol. Gen. Genet.253 (1-2), 205-216.
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Progress 01/01/97 to 12/01/97
Outputs
Genetic map-based cloning has been used to isolate two genes of the fungus PHYTOPHTHORA SOJAE which determine cultivar-specific avirulence (Avr1b and Avr1k). Detailed genetic mapping has been used to localize Avr1b to an 18 kb region. DNA sequencing of a 60 kb region surrounding Avr1b has begun, to help identify Avr1b, and as a pilot project for sequencing the entire P. SOJAE genome. A project to physically map all of the genes of P. SOJAE by hybridization fingerprinting has reached about one third completion. Genetic markers close to genes involved in recognition of soybean by P. SOJAE (chemotaxis) genes have been tentatively identified. In a project on the mechanisms of gene expression in fungi, a transcription factor involved in carbon catabolite repression in NEUROSPORA CRASSA, cre-1, has been shown NOT to be involved in carbon regulation of ribosomal RNA and protein genes.
Impacts
(N/A)
Publications
- CUJEC, T. P., and TYLER, B. M. 1996. Nutritional and Growth Control of RibosomalProtein mRNA and rRNA in NEUROSPORA CRASSA. Nucl. Acids Res. 24(5), 943-950. MA0, Y., and TYLER, B. M. 1996. Cloning and Sequence Analysis of Elicitin Genes of PHYTOPHTHORA SOJAE. Fungal Genet. Biol. 20(2),169-172.
- CUJEC, T. P., and TYLER, B. M. 1996. Functional Promoter Elements Common to Ribosomal Protein and Ribosomal RNA Genes in NEUROSPORA CRASSA. Mol. Gen. Genet.253 (1-2), 205-216.
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Progress 01/01/96 to 12/30/96
Outputs
The aims of this project are: 1) Understand the molecular basis of host specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, genetic map-based cloning has been used to isolate two genes of the fungus PHYTOPHTHORA SOJAE which determine cultivar-specific avirulence (Avr1b and Avr1k). A project to physically map all of the genes of P. SOJAE has been initiated. In a related project, transcription factors in tobacco cells have been tentatively identified which may be targets of a potential toxin from PHYTOPTHTHORA species. In section 2, been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part of this machinery and their functions have been partially
characterized.
Impacts
(N/A)
Publications
- CUJEC, T. P., and TYLER, B. M. 1996. Nutritional and Growth Control of RibosomalProtein mRNA and rRNA in NEUROSPORA CRASSA. Nucl. Acids Res. 24(5), 943-950. MA0, Y., and TYLER, B. M. 1996. Cloning and Sequence Analysis of Elicitin Genes of PHYTOPHTHORA SOJAE. Fungal Genet. Biol. 20(2),169-172.
- CUJEC, T. P., and TYLER, B. M. 1996. Functional Promoter Elements Common to Ribosomal Protein and Ribosomal RNA Genes in NEUROSPORA CRASSA. Mol. Gen. Genet.253 (1-2), 205-216.
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Progress 01/01/95 to 12/30/95
Outputs
The aims of this project are: 1) Understand the molecular basis of host specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, genetic outcrossing of the fungus PHYTOPHTHORA SOJAE has been used to demonstrate the presence of single genes which determine cultivar specific avirulence. Pieces of DNA very close to one of these genes have been identified. In a related project, receptors on tobacco cells have been tentatively identified which may enable the plant to detect and repel many PHYTOPHTHORA species. In section 2, substantial progress has been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part of this machinery and their functions have been
partially characterized.
Impacts
(N/A)
Publications
- TYLER, B. M., FORSTER, H., and COFFEY, M. D. 1995. Inheritance of avirulence factors and RFLP markers in outcrosses of the oomycete PHYTOPHTHORA SOJAE. Mol. Plant-Microbe Ints. 8(4):515-523.
- GIJZEN, M., FORSTER, H., COFFEY, M. D., and TYLER, B. M. 1996. Cosegregation of Avr4 and Avr6 in PHYTOPHTHORA SOJAE. Can. J. Bot. in-press.
- MAO, Y., and TYLER, B. M. 1996. The PHYTOPHTHORA genome contains tandem repeat sequences which vary from strain to strain. Exp. Mycol. in-press.
- TYLER, B. M., and HOLLAND, M. 1995. RNA polymerases and transcription factors of fungi. IN: The Mycota. A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research. WESSELS, J. G. H., and MEINHARDT, F.
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Progress 01/01/94 to 12/30/94
Outputs
The aims of this project are: 1) Understand the molecular basis of host-specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, genetic outcrossing of the fungus PHYTOPHTHORA SOJAE has been used to demonstrate the presence of single genes which determine cultivar-specific avirulence. Also, RFLPs have been used to show how new races of this pathogen have appeared in soybean-growing areas of the country. In a related project, receptors on tobacco cells have been tentatively identified which may enable the plant to detect and repel many PHYTOPHTHORA species. In section 2, substantial progress has been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part
of this machinery and their functions have been partially characterized. The gene encoding two transcription factors from N. CRASSA has been cloned and the properties of the protein encoded by them have been characterized.
Impacts
(N/A)
Publications
- KAMOUN, S., YOUNG, M., FORSTER, H., COFFEY, M. D., and TYLER, B. M. 1994. Potential role of elicitins in the interaction between PHYTOPHTHORA species and tobacco. Appl. Environ. Microbiol. 60(5), 1593-1598.
- FORSTER, H., TYLER, B. M., and COFFEY, M. D. 1994. PHYTOPHTHORA SOJAE races have arisen by clonal evolution and by rare outcrosses. Mol. Plant-Microbe Ints. 7(6), 780-791.
- TYLER, B. M., and HOLLAND, M. 1995. RNA polymerases and transcription factors of fungi. IN: The Mycota. A comprehensive treatise on fungi as experimental systems for basic and applied research. WESSELS, J. G. H. and MEINHARDT, F.
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Progress 01/01/93 to 12/30/93
Outputs
The aims of this project are: 1) Understand the molecular basis of host-specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, genetic outcrossing of the fungus PHYTOPHTHORA SOJAE has been used to demonstrate the presence of single genes which determine cultivar-specific avirulence. Also, RFLPs have been used to show how new races of this pathogen have appeared in soybean-growing areas of the country. In a related project, receptors on tobacco cells have been tentatively identified which may enable the plant to detect and repel many PHYTOPTHTHORA species. In section 2, substantial progress has been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part
of this machinery and their functions have been partially characterized. The gene encoding two transcription factors from N.CRASSA has been cloned and the properties of the protein encoded by them have been characterized.
Impacts
(N/A)
Publications
- KAMOUN, S., KLUCHER, K. COFFEY, M. D., and TYLER, B. M. 1993. A gene encoding a host-species specific protein elicitor of PHYTOPHTHORA PARASITICA. Mol. Plant-Microbe Ints. 6:573-581.
- TYLER, B. M. 1993. To kill or not to kill: the genetic relationship between a parasite and an endophyte Trends in Microbiol. 1:252-254.
- KAMOUN, S., YOUNG, M., FORSTER, H., COFFEY, M. D., and TYLER, B. M. 1994. Potential role of elicitins in the interaction between PHYTOPHTHORA species and tobacco. Appl. Environ. Microbiol. 60(5), in press.
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Progress 01/01/92 to 12/30/92
Outputs
The aims of this project are: 1) understand the molecular basis of host-specificity of selected fungal pathogens and 2) define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, a procedure of genetic outcrossing of the fungus PHYTOPHTHORA SOJAE has been developed for the first time, based on Random Amplified Polymorphic DNAs. This is being used to carry out genetic analysis of cultivar-specific avirulence. Also a procedure for introducing cloned DNA into this fungus has been developed. In P. PARASITICA, a protein has been isolated from the fungus which may enable this fungus to be detected and repelled by the defense system of tobacco plants. Gels encoding these fungal proteins have been cloned and sequenced. In section 2, substantial progress has been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus
NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part of this machinery and their functions have been partially characterized. The gene encoding one transcription factor from N. CRASSA has been cloned and the properties of the protein encoded by it have been characterized.
Impacts
(N/A)
Publications
- JUDELSON, H.S., TYLER, B.M., and MICHELMORE, R.W. 1992. Regulatory sequences for expressing genes in oomycete fungi. Mol. Gen. Genet. 234(1):138-146.
- JUDELSON, H.S., COFFEY, M.D., ARREDONDO, F. and TYLER, B.M. 1993. Transformation of the oomycete pathogen PHYTOPHTHORA MEGASEPRMA f. sp. GLYCINEA occurs by DNA integration to single or multiple chromosomes. Current Genetics (in press).
- KAMOUN, S., YOUNG, M., GLASCOCK, C. and TYLER, B.M. 1993. Extra-cellular protein elicitors of PHYTOPHTHORA: host-specificity and induction of resistance to bacterial and fungal phytopathogens. Mol. Plant-Microbe Ints. (in press).
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Progress 01/01/91 to 12/30/91
Outputs
The aims of this project are: 1) Understand the molecular basis of host-specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. In section 1, a large range of races of the soybean pathogen PHYTOPHTHORA MEGASPERMA f. sp. GLYCINEA (Pmg) have been characteried by RFLP analysis, in collaboration with Dr. Michael Coffery and Dr. Helga Forster (University of California, Riverside). The results suggest that the different races of Pmg derive from three or more distinct progenitor populations and that the races have interbred to some extent. Three RFLP correlating with the presence of cultivar specificity genes were also identified. In P. PARASITICA, a protein has been isolated from the fungus which may enable this fungus to be detected and repelled by the defense system of tobacco plants. Genes encoding these fungal proteins have been cloned. In section 2, substantial progress has been made in
characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and protein (called transcription factors) have been identified as part of this machinery and their functions have been partially characterized. The gene encoding one transcription factor from N. CRASSA has been cloned and sequenced.
Impacts
(N/A)
Publications
- SHI, Y. and TYLER, B.M. 1991. Coordinate Expression of Ribosomal Protein Genes in NEUROSPORA CRASSA and Identification of Conserved Upstream Sequnces. Nucl. Acids Res. 19(23):6511-6517.
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Progress 01/01/90 to 12/30/90
Outputs
The aims of this project are :1) Understand the molecular basis of host-specificity of selected fungal pathogens. 2) Define the molecular mechanisms by which fungal genes are expressed and regulated. The work in section 1 is relatively preliminary. Isolates of the fungi PHYTOPHTHORA CAPSICI and PHYTOPHTHORA PARASITICA have been characterized for pathogenicity and host range in preparation for more molecular genetic studies. A protein has been isolated from P. PARASITICA which may enable this fungus to be detected and repelled by the defense system of tobacco plants. In section 2, substantial progress has been made in characterizing the cellular machinery responsible for the function of genes controlling the growth rate of fungi, namely the genes encoding the ribosomes in the fungus NEUROSPORA CRASSA. Several DNA sequences and proteins (called transcription factors) have been identified as part of this machinery and their functions have been partially characterized. The
gene encoding one transcription factor from N.CRASSA has been cloned and sequenced.
Impacts
(N/A)
Publications
- TYLER, B.M. and HARRISON, K. (1990) `A NEUROSPORA CRASSA Ribosomal Protein Gene, Homologous to Yeast CRY1, Contains Sequences Potentially Coordinating its Transcription with rRNA Genes' Nucl. Acids. Res. 18(19), 5759-5765.
- SHI,Y. and TYLER, B.M. (1991) "All Internal Elements of NEUROSPORA CRASSA 5S rRNA and tRNA genes, including the A boxes, are Transcriptionally Gene-Specific' J. Biol. Chem. 266(13), 8015-8019.
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