Progress 10/01/06 to 09/30/11
Outputs
OUTPUTS: This project supported six major activities: The first activity was analysis of the H. arabidopsidis genome sequence. With the two other groups, we generated a high quality, annotated assembly of the Hpa genome, along with web browsers, a training conference, and an annotation jamboree to facilitate full utilization of the genome. We led a community effort to compare the Hpa genome to the genomes of related, hemi-biotrophic Phytophthora species, to gain insight into the molecular basis and evolution of obligate biotrophy. Compared to Phytophthora genomes, the Hpa genome exhibits dramatic reductions in genes encoding: 1) RXLR effectors and other secreted pathogenicity proteins; 2) enzymes for assimilation of inorganic nitrogen and sulphur; 3) proteins associated with zoospore formation and motility. The second activity is analysis of regulation of the RPP8 pathogen resistance gene from Arabidopsis. This project revealed molecular pathways that regulate the activity of this surveillance gene, and provided the first evidence that pathogen surveillance genes are subject to regulation by WRKY proteins that had previously been associated with downstream steps in the immune signaling network. The third activity was to characterize oomycete effector proteins that are evolutionarily conserved between H. arabidopsidis and the soybean rot pathogen Phytophthora sojae. We established that several pairs of conserved RXLR proteins are bona fide effectors that can suppress plant immune responses in distantly related plant species. We conducted detailed analysis of two pairs of evolutionarily conserved effectors: Hpa effector Ha96 and its homolog from P. sojae, Ps163, and Ha23 and its P. sojae homolog Ps73. We have obtained data indicating that Ha96 and Ps163 promote virulence from within the plant cell nucleus, and interact with specific Arabidopsis E3 ubiquitin ligases and their homologs in soybean. Surprisingly, Ha23 shares functional and structural similarity with the conserved Pseudomonas effector AvrE. The fourth activity was to develop a quantitative PCR assay to measure growth of H. arabidopsidis in planta. This enables accurate detection of small changes in virulence. The fifth activity was to test whether entry of effector proteins into host cells can be inhibited by transgenic expression of proteins that bind to membrane phospholipids. This work generated data that supported a successful grant proposal to the USDA-NIFA Global Food Security Program to develop new tools to combat oomycete diseases of soybean. The sixth activity was to continue a collaboration with an outreach program at Virginia Tech that uses mutant and transgenic Arabidopsis as teaching tools for high school science education. Several high school classes analyzed transgenic Arabidopsis expressing the Ha96 and Ps163 effector proteins, and obtained evidence that these proteins affect the plants' ability to resist environmental stress. This collaboration involved approximately 450 students and 16 teachers at 9 schools. Results from these projects were disseminated through the publications listed below and through presentations at several international meetings and invited seminars. PARTICIPANTS: The H. arabidopsidis draft genome sequence was generated in collaboration with the following principle investigators: Dr. Brett Tyler, Virginia Bioinformatics Institute, Dr. Sandra Clifton, Washington University Genome Sequencing Center, Dr. Jim Beynon, Horticulture Research International, UK, Dr. Jane Rogers, Sanger Genome Center, UK , and Dr. Jonathan Jones, Sainsbury Laboratories, UK. Experimental characterization of effectors was performed in my lab by two Ph.D. students: Mr. Ryan Anderson and Ms. Devdutta Deb, and by four undergraduates: Theresa How-Yew Kin, Megan Cassady, Rachel Fee, and Dan Deegan. Mr. Anderson's and Ms. Deb's work comprises major portions of their dissertations. For the Outreach component of this project, we collaborated with David Lalley and Erin Dolan at Virginia Tech. TARGET AUDIENCES: The immediate target audience is comprised of scientists that are interested in the molecular basis of plant-pathogen interactions. As described above, our research findings are disseminated by presentations at professional meetings and publications in books and peer-reviewed journals. As described above, our outreach collaboration is designed for a target audience of high school students and teachers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The research will help lay the groundwork for understanding how plants are colonized and destroyed by oomycete pathogens. Our analysis of the H. arabidopsidis genome provides the first insight into the molecular basis and evolution of obligate biotrophy, in which pathogens are dependent on living host cells and can't survive apart from their hosts. One major finding of this study is that the H. arabidopsidsis genome contains significantly reduced numbers of genes encoding cell-wall degrading proteins, secreted proteases, and other proteins that might provoke host defenses, compared to Phytophthora. Thus, the genome appears to be optimized for stealth inside the host. Another major finding is that several metabolic pathways have been lost after the divergence of downy mildews, indicative of evolution towards metabolic dependency on the host. Our analysis of effectors is providing insight into the molecular weaponry that oomycetes use to create a more favorable niche in plant cells. We have established that oomycete effectors cause similar effects (i.e. suppression of immune responses) from different locations in the cell. This research is relevant to crop security on national and global scales. Downy mildew diseases account for approximately 20% of the $4.7 billion world fungicide market, and two downy mildews are considered as significant potential threats to US corn production and are listed among the top ten potential plant bioterror threats. Downy mildews and other oomycetes are unaffected by the majority of fungicides and therefore are very difficult to control. Additionally, many oomycetes have displayed an extraordinary ability to overcome chemical control measures and genetic resistance bred into plant hosts. Thus, there is a critical need for new control strategies. For example, by focusing on evolutionarily conserved effectors, we hope to reveal important weapons that are utilized by all oomycetes. Our long-term goal is to explore whether conserved effectors could represent points of pathogen vulnerability that could be targeted with new genetic strategies, to reduce disease. The USDA-NIFA grant will fund several projects aimed at translating genome data into practical solutions for crop diseases. Our contribution to this project will be to screen for durable resistance genes in soybean germplasm. The outreach activities described above have disseminated our research, and more importantly, the impact of plant microbe interactions, to a broader audience than would be reached through typical channels of academic dissemination.
Publications
- Baxter L, Tripathy S, Ishaque N, Boot N, Cabral A, Kemen E, Thines M, Ah-Fong A, Anderson R, Badejoko W, Bittner-Eddy P, Boore JL, Chibucos MC, Coates M, Dehal P, Delehaunty K, Dong S, Downton P, Dumas B, Fabro G, Fronick C, Fuerstenberg SI, Fulton L, Gaulin E, Govers F, Hughes L, Humphray S, Jiang RH, Judelson H, Kamoun S, Kyung K, Meijer H, Minx P, Morris P, Nelson J, Phuntumart V, Qutob D, Rehmany A, Rougon-Cardoso A, Ryden P, Torto-Alalibo T, Studholme D, Wang Y, Win J, Wood J, Clifton SW, Rogers J, Van den Ackerveken G, Jones JD, McDowell JM, Beynon J, Tyler BM., 2010, Signatures of Adaptation to Obligate Biotrophy in the Hyaloperonospora arabidopsidis Genome. Science, 330:1549-1551.
- McDowell JM, 2011, Genomes of obligate plant pathogens reveal adaptations for obligate parasitism. Proc Natl Acad Sci USA, 108:8921-2.
- McDowell J.M., Hoff, T., Anderson, R., Deegan, D., 2011, Propogation, Storage, and Assays with Hyaloperonospora arabidopsidis, a model oomycete pathogen of Arabidopsis, Methods in Molecular Biology, 712:137-51.
- McDowell J.M., 2011, Examples of How New Experimental Technologies Have Enabled Landmark Advances in Understanding of Plant Immunity Over the Last Half-Century, Methods in Molecular Biology, 712:v-x.
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Progress 10/01/09 to 09/30/10
Outputs
OUTPUTS: The oomycete pathogen Hyaloperonospora arabidopsidis causes downy mildew disease on the model plant Arabidopsis thaliana. H. arabidopsidis is representative of a large group of downy mildew species that collectively parasitize hundreds of plant species. This project supported five major activities in the previous year, each of which is designed to provide insight into the molecular basis of oomycete diseases. The first activity is analysis of the H. arabidopsidis genome sequence. We concluded our analysis of the genome. A manuscript describing this work was accepted by Science and will be published in December. The second activity is analysis of regulation of the RPP8 pathogen resistance gene from Arabidopsis. A manuscript describing this work was published in Molecular Plant-Microbe Interactions. The third activity is to characterize oomycete effector proteins that are evolutionarily conserved between H. arabidopsidis and the soybean rot pathogen Phytophthora sojae. We are focusing on two effectors called Ha98 and Ha23, and continued to analyze the functions of these proteins and their homologs in P. sojae during the previous year. It is now clear that all of these proteins can suppress multiple aspects of the immune response. A manuscript describing the initial characterization of Ha98 is almost complete and will be submitted by January 2011. A second manuscript, describing Ha23, will be submitted by Spring 2011. The fourth activity was to develop a quantitative PCR assay to measure growth of H. arabidopsdis in planta. This enables accurate detection of small changes in virulence. We will publish this assay in Winter 2011. The fifth activity was to test whether entry of effector proteins into host cells can be inhibited by transgenic expression of proteins that bind to membrane phospholipids. This work generated preliminary data that supported a successful grant proposal ($9.5 million) to the USDA-NIFA Global Food Security Program to develop new tools to combat oomycete diseases of soybean. The sixth activity was to continue a collaboration with an outreach program at Virginia Tech that uses mutant and transgenic Arabidopsis as teaching tools for high school science education. Specifically, several high school classes analyzed transgenic Arabidopsis expressing the Ha98 and Ps163 effector proteins, and obtained evidence that these proteins enhance the plants' ability to resist environmental stress. Based in part on this collaboration, we were successful in obtaining funding ($2.4 million) from the NSF GK-12 program to enable molecular plant science graduate students at Virginia Tech to set up similar collaborations with high school classes. Results from these projects were disseminated through the publications listed below and through presentations at three international meetings and invited seminars. PARTICIPANTS: The H. arabidopsidis draft genome sequence was generated in collaboration with the following principle investigators: Dr. Brett Tyler, Virginia Bioinformatics Institute, Dr. Sandra Clifton, Washington University Genome Sequencing Center, Dr. Jim Beynon, Horticulture Research International, UK, Dr. Jane Rogers, Sanger Genome Center, UK , and Dr. Jonathan Jones, Sainsbury Laboratories, UK. Experimental characterization of effectors was performed in my lab by two Ph.D. students: Mr. Ryan Anderson and Ms. Devdutta Deb, and by two undergraduates: Ms. Theresa How-Yew Kin, and Ms. Megan Cassady. Mr. Anderson's and Ms. Deb's work in the previous year will comprise major portions of their dissertations. For the Outreach component of this project, we collaborated with David Lalley and Erin Dolan at Virginia Tech. TARGET AUDIENCES: The immediate target audience is comprised of scientists that are interested in the molecular basis of plant-pathogen interactions. As described above, our research findings are disseminated by presentations at professional meetings and publications in books and peer-reviewed journals. As described above, our outreach collaboration is designed for a target audience of high school students and teachers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The research described above will help lay the groundwork for understanding how plants are colonized and destroyed by oomycete pathogens. Our analysis of the H. arabidopsidis genome provides the first insight into the molecular basis and evolution of obligate biotrophy, in which pathogens are dependent on living host cells and can't survive apart from their hosts. One major finding of this study is that the H. arabidopsidsis genome contains significantly reduced numbers of genes encoding cell-wall degrading proteins, secreted proteases, and other proteins that might provoke host defenses, compared to Phytophthora. Thus, the genome appears to be optimized for stealth inside the host. Another major finding is that several metabolic pathways have been lost after the divergence of downy mildews, indicative of evolution towards metabolic dependency on the host. Our analysis of effectors is providing insight into the molecular weaponry that oomycetes use to create a more favorable niche in plant cells. We have established that oomycete effectors cause similar effects (i.e. suppression of immune responses) from different locations in the cell. This research is relevant to crop security on national and global scales. Downy mildew diseases account for approximately 20% of the $4.7 billion world fungicide market, and two downy mildews are considered as significant potential threats to US corn production and are listed among the top ten potential plant bioterror threats. Downy mildews and other oomycetes are unaffected by the majority of fungicides and therefore are very difficult to control. Additionally, many oomycetes have displayed an extraordinary ability to overcome chemical control measures and genetic resistance bred into plant hosts. Thus, there is a critical need for new control strategies. For example, by focusing on evolutionarily conserved effectors, we hope to reveal important weapons that are utilized by all oomycetes. Our long-term goal is to explore whether conserved effectors could represent points of pathogen vulnerability that could be targeted with new genetic strategies, to reduce disease. The USDA-NIFA grant will fund several projects aimed at translating genome data into practical solutions for crop diseases. Our contribution to this project will be to screen for durable resistance genes in soybean germplasm. The outreach activities described above have disseminated our research, and more importantly, the impact of plant microbe interactions, to a broader audience than would be reached through typical channels of academic dissemination.
Publications
- McDowell J.M., Baxter L., Tripathy S., Rogers J., Clifton S., Beynon J., and Tyler B.M. (2009) Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Conference Proceedings, Plant and Animal Genome Conference, January 2010.
- Anderson R. G., Fee R. A., Deb D., Kale S. D., Tyler B. M., and McDowell J. M. (2009) Characterizing Conserved Effector Proteins From Hyaloperonospora arabidopsidis, Conference Proceedings, Oomycete Molecular Genetics Network, Toulouse, France, June 2010.
- McDowell J.M., Baxter L., Tripathy S., Rogers J., Clifton S., Beynon J., and Tyler B.M. (2009) Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Conference Proceedings, Oomycete Molecular Genetics Network, Toulouse, France, June 2010.
- Mohr, T. J., Mammarella, N. T., Hoff, T., Woffenden, B. W., Jelesko, J. G., and McDowell, J. M., 2010, The Arabidopsis downy mildew resistance gene RPP8 is induced by pathogens and salicylic acid, and is regulated by W box cis elements. Molecular Plant-Microbe Interactions, 23:1303-15.
- Baxter L, Tripathy S, Ishaque, N et al (2010) Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Science xx: xx-yy.
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Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: The oomycete pathogen Hyaloperonospora arabidopsidis causes downy mildew disease on the model plant Arabidopsis thaliana. H. arabidopsidis is representative of a large group of downy mildew species that collectively parasitize hundreds of plant species. This project supports two major activities, each of which is designed to provide insight into the molecular basis of oomycete diseases. The first activity is analysis of the H. arabidopsidis genome sequence. This project is a collaboration between labs in the United States, the United Kingdom and the Netherlands, and has been funded by the USDA/NSF Microbial Genome Sequencing Program. During the past year, we significantly improved the quality of the draft genome by integrating 100 fully sequenced bacterial artificial chromosomes and approximately 4 MB of new sequence generated by Illumina technology. The resulting assembly contains greater than 95 percent of H. arabidopsidis gene space. We are now repeating key analyses to ensure that the major conclusions from analysis of the previous assembly are still valid. We expect to complete these and submit a major manuscript in Winter 2010. The second activity is to characterize oomycete effector proteins that are evolutionarily conserved between H. arabidopsidis and the soybean rot pathogen Phytophthora sojae. Effector proteins are secreted by pathogens to the inside of plant cells, in which they target regulatory networks to create a better niche for the pathogen. The roles of effectors in oomycete pathogenesis are only beginning to be explored. We are focusing on two effectors called Ha98 and Ha23. In the previous year, we completed experiments to prove that Ha98 and its homolog in Phytophthora sojae, Ps163, are both bona fide effectors that are expressed during infection and can enter plant cells. We also showed that both effectors can suppress multiple immune responses when expressed transgenically in multiple plant species. Finally, we added to preliminary evidence suggesting that these effector act in the plant cell nucleus. For Ha23, we demonstrated that these effector gene is expressed during infection and can suppress immunity in Arabidopsis and soybean. Interestingly, this effector appears to target chloroplasts, making this the first oomycete effector known to target this organelle. Results from these activities were disseminated in presentations at five international conferences. In addition, this project supported three book chapters and editing of a book describing lab methodology in plant immunity. Our lab instructed and participated in an oomycete genomics training workshop. Finally, we initiated a collaboration with an outreach program at Virginia Tech, which uses mutant, and transgenic Arabidopsis as teaching tools for high school science education. Specifically, several classes analyzed transgenic Arabidopsis expressing the Ha98 and Ps163 effector proteins. As part of this collaboration, two videos describing the research in lay terms were produced and disseminated via the Internet. PARTICIPANTS: The H. parastica draft genome sequence was generated in collaboration with the following principle investigators: Dr. Brett Tyler, Virginia Bioinformatics Institute, Dr. Sandra Clifton, Washington University Genome Sequencing Center, Dr. Jim Beynon, Horticulture Research International, UK, Dr. Jane Rogers, Sanger Genome Center, UK , and Dr. Jonathan Jones, Sainsbury Laboratories, UK. Experimental characterization of effectors was performed in my lab by two Ph.D. students: Mr. Ryan Anderson and Ms. Devdutta Deb, and by three undergraduates: Ms. Rachel Fee, Ms. Theresa How-Yew Kin, and Ms. Megan Cassady. Mr. Anderson's and Ms. Deb's work in the previous year will comprise major portions of their dissertations. Ms. Fee's work formed the basis of a Senior Undergraduate Honors Thesis that she successfully defended in Spring 2009. For the Outreach component of this project, we collaborated with David Lalley and Erin Dolan at Virginia Tech. TARGET AUDIENCES: The immediate target audience is comprised of scientists that are interested in the molecular basis of plant-pathogen interactions. As described above, our research findings are disseminated by presentations at professional meetings and publications in books and peer-reviewed journals. As described above, our outreach collaboration is designed for a target audience of high school students and teachers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The research described above will help lay the groundwork for understanding how plants are colonized and destroyed by oomycete pathogens. Our analysis of the H. arabidopsidis genome provides the first insight into the molecular basis and evolution of obligate biotrophy, in which pathogens are dependent on living host cells and can't survive apart from their hosts. One major finding of this study is that the H. arabidopsidsis genome contains significantly reduced numbers of genes encoding cell-wall degrading proteins, secreted proteases, and other proteins that might provoke host defenses, compared to Phytophthora. Thus, the genome appears to be optimized for stealth inside the host. Another major finding is that several metabolic pathways have been lost after the divergence of downy mildews, indicative of evolution towards metabolic dependency on the host. Our analysis of effectors is providing insight into the molecular weaponry that oomycetes use to create a more favorable niche in plant cells. We have established that oomycete effectors cause similar effects (i.e. suppression of immune responses) from different locations in the cell. This research is relevant to crop security on national and global scales. Downy mildew diseases account for approximately 20 percent of the $4.7 billion world fungicide market, and two downy mildews are considered as significant potential threats to US corn production and are listed among the top ten potential plant bioterror threats. Downy mildews and other oomycetes are unaffected by the majority of fungicides and therefore are very difficult to control. Additionally, many oomycetes have displayed an extraordinary ability to overcome chemical control measures and genetic resistance bred into plant hosts. Thus, there is a critical need for new control strategies. For example, by focusing on evolutionarily conserved effectors, we hope to reveal important weapons that are utilized by all oomycetes. Our long-term goal is to explore whether conserved effectors could represent points of pathogen vulnerability that could be targeted with new genetic strategies, to reduce disease. The outreach activities described above have disseminated our research, and more importantly, the impact of plant microbe interactions, to a broader audience than would be reached through typical channels of academic dissemination.
Publications
- McDowell J.M., Baxter L., Tripathy S., Rogers J., Clifton S., Beynon J., and Tyler B.M. (2009) Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Chapter X in Anton, H (ed.), Biology of Plant-Microbe Interactions, Vol. 6 (in press)
- McDowell, J.M. (2010) Examples of how new experimental technologies have enabled landmark advances in understanding of plant immunity over the last half-century. Chapter 1 in J.M. McDowell, Methods in Molecular Biology (ed.), The Plant Immune System (in press)
- McDowell, J.M., Hoff, T., Anderson, R.G., and Deegan D (2010) Propagation, Storage, and Assays with Hyaloperonospora arabidopsidis, a Model Oomycete Pathogen of Arabidopsis. Chapter 12 in J.M. McDowell (ed.), Methods in Molecular Biology, The Plant Immune System (in press)
- Anderson R. G., Fee R. A., Deb D., Kale S. D., Tyler B. M., and McDowell J. M. (2009) Characterizing Conserved Effector Proteins From Hyaloperonospora arabidopsidis, Conference Proceedings, Oomycete Molecular Genetics Network, Sailorman CA, March 2009 (P12).
- McDowell J.M., Baxter L., Tripathy S., Rogers J., Clifton S., Beynon J., and Tyler B.M. (2009) Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Conference Proceedings, Oomycete Molecular Genetics Network, Asilomar CA, March 2009 (P15).
- Anderson R. G., Fee R. A., Deb D., Kale S. D., Tyler B. M., and McDowell J. M. (2009) Conserved Oomycete Effector Proteins Suppress Programmed Cell Death. Proceedings of the 14th Congress for the International Society for Molecular Plant-Microbe Interactions, Quebec City, CA
- Tyler B. M., Tripathy S., Kale S. D., Zhou L., Ferreira A., Dou D., Arredondo F. D., Mideros S. X., Bao L., Krampis K., Jerauld A., Cooper K., Qunqing W., Changzhi H., Gu B., Anderson R.G., Hanlon R., Xiaoli W., Xiaoli Y., Tiuli L., Yao Y., Xinle W., Suomeng D., Zhengguang Z., Xiaobo Z., Evans C., Shan W., Wang Y., St. Martin S. K., Saghai Maroof M. A., Hoeschele I., Dorrance A. E., McDowell J.M. (2009) Comparative and functional genomics of oomycete infection. Phytopathology 99:S164
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Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: The oomycete pathogen Hyaloperonospora arabidopsidis (formerly Hyaloperonospora parasitica) causes downy mildew disease on the model plant Arabidopsis thaliana. H. arabidopsidis is representative of a large group of downy mildew species that collectively parasitize hundreds of plant species. We have generated a draft sequence of the H. arabidopsidis genome, in collaboration with labs in the United States and the United Kingdom, with funding from the USDA/NSF Microbial Genome Sequencing Program. During the past year, we completed the annotation of the H. Arabidopsis genome and we coordinated a distributed analysis of the genome by a number of oomycete research labs. This effort provided the first insights into the genomic structure and evolution of an obligate biotroph pathogen (dependent on living host tissue). Most of the effort was focused on comparisons between the H. arabidopsidis genome and genomes from related Phytophthora pathogens that trigger host cell death in the latter stages of their life cycle. The major finding of this study is that the H. arabidopsidsis genome contains significantly reduced numbers of genes encoding cell-wall degrading proteins, secreted proteases, and other proteins that might provoke host defenses, compared to Phytophthora. Thus, the genome appears to be optimized for stealth inside the host, consistent with an obigate biotroph lifestyle. We are currently preparing a manuscript describing this effort for submission to Nature. Our second focus has been to characterize oomycete effector proteins that are conserved between H. arabidopsidis and the soybean rot pathogen Phytophthora sojae. Effector proteins are secreted by pathogens to the inside of plant cells, in which they target regulatory networks to create a better niche for the pathogen. The roles of effectors in oomycete pathogenesis are only beginning to be explored. Our research has provided evidence that several effectors function to suppress plant immune responses in soybean and Arabidopsis. In one case, this function appears to require translocation of the effector protein to the host cell nucleus, suggesting that these effectors function by reprogramming host gene expression. In another case, the effector appears to target chloroplasts, making this the first oomycete effector known to target this organelle. This research was presented at two international conferences (Anderson et al.) and led to one peer-reviewed publication (Dou et al). PARTICIPANTS: The H. parastica draft genome sequence was generated in collaboration with the following principle investigators: Dr. Brett Tyler, Virginia Bioinformatics Institute, Dr. Sandra Clifton, Washington University Genome Sequencing Center, Dr. Jim Beynon, Horticulture Research International, UK, Dr. Jane Rogers, Sanger Genome Center, UK Experimental characterization of effectors was performed in my lab by a Ph.D. student, Mr. Ryan Anderson, a graduate rotation student, Ms. Devdutta Deb, and an undergraduate, Ms. Rachel Fee. Mr. Anderson's work in the previous year will form the bulk of the second chapter of his dissertation. Ms. Fee's work will form the basis of a Senior Undergraduate Honors Thesis TARGET AUDIENCES: The immediate target audience is comprised of scientists that are interested in the molecular basis of plant-pathogen interactions. As described above, our research findings are disseminated by presentations at professional meetings and publications in peer-reviewed journals. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This research lays the groundwork for a change in knowledge of the molecular weapons that oomycete pathogens use to cause disease. This is relevant to crop security on national and global scales. Downy mildew diseases account for approximately 20% of the $4.7 billion world fungicide market, and two downy mildews are considered as significant potential threats to US corn production and are listed among the top ten potential plant bioterror threats. Downy mildews and other oomycetes are unaffected by the majority of fungicides and therefore are very difficult to control. Additionally, many oomycetes have displayed an extraordinary ability to overcome chemical control measures and genetic resistance bred into plant hosts. Thus, there is a critical need for new control strategies. By focusing on evolutionarily conserved effectors, we hope to reveal important weapons that are utilized by all oomycetes. Our long-term goal is to explore whether conserved effectors could represent points of pathogen vulnerability that could be targeted with new genetic strategies, to reduce disease.
Publications
- Dou, D., Kale, S. D., Wang, X., Chen, Y., Wang, Q., Wang, X., Jiang, R. H. Y., Arredondo, F. D., Anderson, R.G., Thakur, P. B., McDowell, J. M., Wang, Y., Tyler, B. M. (2008) Conserved C-terminal motifs required for avirulence and suppression of cell death by Phytophthora sojae effector Avr1b. The Plant Cell, 20: 1118-1133.
- R. G. Anderson, P. Thakur, S. D. Kale, R. H. Y. Zhang, D. Dou, X. Wang, B. M. Tyler, J. M. McDowell (2008), Characterizing Conserved Effector Proteins From Hyaloperonospora parasitica, Conference Proceedings, Keystone Symposium of Plant Innate Immunity, Keystone, CA, February 2008 (P126).
- R. G. Anderson, P. Thakur, S. D. Kale, R. H. Y. Zhang, D. Dou, X. Wang, B. M. Tyler, J. M. McDowell (2008), Characterizing Conserved Effector Proteins From Hyaloperonospora parasitica, Conference Proceedings, Oomycete Molecular Genetics Network, Asilomar CA, March 2008 (P13).
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Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: The oomycete pathogen Hyaloperonospora parasitica causes downy mildew disease on crucifers, including the model plant Arabidopsis thaliana. We have generated a draft sequence of the H. parasitica genome, in collaboration with labs in the United States and the United Kingdom, with funding from the USDA/NSF Microbial Genome Sequencing Program. We have used this draft genome to identify genes that encode putative "effector" proteins that are secreted by the pathogen to the interior of plant cells, to suppress defense responses in the plant and perhaps alter cell structure and/or metabolism. Effector proteins have been shown to play key roles in bacterial pathogenesis. In contrast, the roles of effectors in oomycete pathogenesis are only beginning to be explored. Recent studies of known oomycete effectors have revealed conserved protein motifs that are required for targeting of the proteins to the interior of host cells. These motifs have high predictive value for identifying
new candidate effectors, using bioinformatic screens. We have identified 200 candidate effector genes in the genome of Hyaloperonospora parasitica. Approximately half of these predicted effectors contain two C-terminal motifs (W and Y) that have a predicted structure similar to some transcription factors. We are currently focusing on eight effectors that are conserved between H. parasitica and the soybean rot pathogen Phytophthora sojae. We test the hypothesis that these effectors have common roles in infection by the two oomycete pathogens. Four of these effector sets carry a conserved nuclear localization signal (NLS), suggesting that these effectors manipulate host gene expression. For several of these genes, we have confirmed expression in planta and have verified that the predicted NLS is functional in plant cells. We have developed an assay to confirm that predicted effector proteins are translocated to host cells. Finally, we have shown that one H. parasitica effector
suppresses programmed cell death, which is a major component of plant defenses. This research was presented at an international conference (Anderson et al.). This project also supported authorship of a peer-reviewed article discussing similarities and differences in plant and animal immune responses (McDowell and Simon).
PARTICIPANTS: The H. parastica draft genome sequence was generated in collaboration with the following principle investigators: Dr. Brett Tyler, Virginia Bioinformatics Institute, Dr. Sandra Clifton, Washington University Genome Sequencing Center, Dr. Jim Beynon, Horticulture Research International, UK, Dr. Jane Rogers, Sanger Genome Center, UK Experimental characterization of effectors was performed in my lab by a Ph.D. student, Mr. Ryan Anderson. His work in the previous year will form the bulk of the first chapter of Mr. Anderson's dissertation.
TARGET AUDIENCES: The immediate target audience is comprised of scientists that are interested in the molecular basis of plant-pathogen interactions. As described above, our research findings are disseminated by presentations at professional meetings and publications in peer-reviewed journals.
PROJECT MODIFICATIONS: We have shifted our focus from plant resistance genes to pathogen effector genes. The main reason for this change in emphasis is that the newly available H. parasitica genome sequence provides a powerful resource to understand how destructive oomycete pathogens cause disease. As described above, we expect that understanding of effector targets and modes of action inside host cells will lead to new strategies for engineering resistant plants and reducing our reliance on chemical inputs.
Impacts
This research lays the groundwork for a change in knowledge of the molecular weapons that oomycete pathogens cause disease. This is relevant to crop security on national and global scales. Downy mildews diseases account for approximately 20% of the $4.7 billion world fungicide market, and two downy mildews are considered as significant potential threats to US corn production and are listed among the top ten potential plant bioterror threats. Downy mildews and other oomycetes are unaffected by the majority of fungicides and therefore are very difficult to control. Additionally, many oomycetes have displayed an extraordinary ability to overcome chemical control measures and genetic resistance bred into plant hosts. Thus, there is a critical need for new control strategies. By focusing on evolutionarily conserved effectors, we hope to reveal important weapons that are utilized by all oomycetes. Our long-term goal is to explore whether conserved effectors could represent
points of pathogen vulnerability that could be targeted with new genetic strategies, to reduce disease.
Publications
- McDowell, J. M. and Simon, S. (200X) Molecular Diversity at the Plant-Pathogen Interface. Developmental and Comparative Immunology, In Press.
- R. G. Anderson, P. Thakur, S. D. Kale, R. H. Y. Zhang, D. Dou, X. Wang, B. M. Tyler, J. M. McDowell (2007), Characterizing Conserved Effector Proteins From Hyaloperonospora parasitica, Conference Proceedings, Oomycete Molecular Genetics Network, Asilomar CA, March 2007 (P16).
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