Progress 12/01/00 to 11/30/05
Outputs
We isolated the Rxo1 gene of maize, which controls a resistance reaction to the bacterial streak pathogen of rice, Xanthomonas oryzae pv. oryzicola. We also isolated the corresponding avirulence gene from the bacterial pathogen. When both are delivered into maize or rice cells together, defense responses are initiated. We also determined that the Rxo1 gene confers resistance to some strains of Burkholdaria andropogonis, the bacterial stripe pathogen of maize and sorghum. We made transgenic maize plants with the Rxo1 gene to demonstrate that the Rxo1 gene controls resistance reactions to both bacterial pathogens.
Impacts
The Rxo1 transgene was demonstrated to control resistance to X. oryzae pv. oryzicola, a pathogen which does not yet occur in US rice growing regions but is on the Select Agent List. This is the first demonstration that a resistance gene can function after transfer between distantly related cereals like maize and rice. This is also the first demonstration that some cereal resistance genes can confer resistance to multiple bacterial genera.
Publications
- Zhao, B., Ardales, E.Y., Brasset, E., Claflin, L.E., Leach, J.E., Hulbert, S.H. (2004) The Rxo1/Rba1 locus of maize controls resistance reactions to pathogenic and nonhost bacteria. Theor. Appl. Genet. 109:71-79
- Monosi, B., Wisser R. J., Pennill, L. and S.H. Hulbert (2004) Full-Genome analysis of resistance gene homologs in rice. Theor Appl Genet. 109(7):1434-47.
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Progress 01/01/04 to 12/31/04
Outputs
We isolated the Rxo1 gene of maize, which controls a resistance reaction to the bacterial streak pathogen of rice, Xanthomonas oryzae pv. oryicola. We also isolated the corresponding avirulence gene from the bacterial pathogen. When both are delivered into maize or rice cells together, defense responses are initiated. We also determined the Rxo1 gene confers resistance to some strain of Burkholdaria andropogonis, the bacterial stripe pathogen of maize and osrghum. We made transgenic maize plants with the Rxo1 gene to demonstrate the Rxo1 gene controls resistance reactions to both bacterial pathogens. We transferred the Rxo1 gene into transgenic rice and demonstrated that it functions to control resistance to bacterial streak in this pathogen.
Impacts
The Rxo1 transfene was demonstrated to control resistance to X.oryae pv oryzicola, a pathogen which does not yet occur in US rice growing regions but is on the Select Agent List. This is the first demonstration a resistance gene can function after transfer between distantly related cereals like maize and rice. This is also the first demonostration some cereal resistance genes can confer resistance to multiple bacterial genera.
Publications
- Zhao, B., Ardales, E. Y., Raymundo, A. Trick, H.,Leach, J.E., and Hulbert, S.H. (2004) The avrRxo1 gene from the rice pathogen Xanthomonas oryzae pv. oryzicola confers a nonhost defense reaction on maize with resistance gene Rxo1. Mol. Plant Microbe Interact 17:771-779.
- Smith, S., and Hulbert, S.H. (2003). Evolution of disease resistance genes. In Genomic and Genetic Analysis of Plant Parasitism and Defense. J.E. Leach, T. Wolpert and S. Tsuyumu, eds. APS Press, St. Paul, MN.
- Zhao, B., Ardales, E.Y., Brasset, E., Claflin, L.E., Leach, J.E., Hulbert, S.H. (2004) The Rxo1/Rha1 locus of maize controls resistance reactions to pathogenic and nonhost bactera. Theor. Appl. Genet. 109:71-79.
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Progress 01/01/03 to 12/31/03
Outputs
Several cereal disease resistance genes are being tested for functionality after transfer to distantly-related cereal crops. One resistance gene we are testing in heterologous cereals is the Rxo1 gene of maize. The Rxo1 gene controls a hypersensitive resistance reaction to the rice bacterial leaf streak disease, caused by Xanthomonas oryzae pv. oryzicola (Xoo) and also controls a resistance reaction to the sorghum bacterial stripe pathogen Burkholderia andropogonis. We isolated an NBS-LRR gene that controls the resistance phenotype when transferred into maize lines that do not carry the Rxo1 gene. We also isolated the Avr gene that interacts with Rxo1 (avrRxo1) to facilitate the molecular characterization of the interaction. When the avrRxo1 gene was placed under control of a plant promoter and bombarded into B73 (Rxo1) maize cells, it induced the HR as indicated by a lack of reporter gene expression. Transient assays indicate the maize Rxo1 gene can detect the
presence of avrRxo1 in rice and initiate defense responses. This was determined by delivering both the Rxo1 and avrRxo1 into leaf cells simultaneously by delivery on micro-projectiles. The results indicate the gene should function to control resistance in rice. We are now transferring the Rxo1 gene to rice to verify that it will confer resistance to the bacterial leaf streak disease. We also transferred maize Rp1 genes to wheat to determine if they can be used to confer leaf rust resistance. Two different Rp1 genes, Rp1-D and Rp1-D21, were transferred to wheat by biolistic transformation techniques. None of the wheat lines showed any noticeable rust resistance. Analysis of the transcripts in the transgenic plants indicated the genes were not being transcribed properly and premature truncation of the transcripts was probably responsible for the lack of expression.
Impacts
Testing the utility of resistance gene transfer between cereals will have a big impact on designing strategies to develop disease resistant cultivars. The Rxo1 gene appears to be working in the heterologous cereal species, rice. If it controls the rice disease this will indicate isolation of pathogen resistance genes from nonhost cereal species is a viable strategy for engineering resistance.
Publications
- Zhao, B., Ardales, E.Y., Brasset, E., Claflin, L.E., Leach, J.E., Hulbert, S.H. 2003. The Rxo1/Rba1 locus of maize controls resistance reactions to pathogenic and nonhost bacteria. Theor. Appl. Genet. In Press
- Zhao, B., Ardales, E. Y., Raymundo, A., Trick, H., and Leach,J. E., Hulbert, S.H. 2003.The avrRxo1 gene from the rice pathogen Xanthomonas oryzae pv. oryzicola confers a nonhost defense reaction on maize with resistance gene Rxo1. Submitted
- Steinau, M., Ayliffe,M.A., Park, R. F., Rooke, L., Pacheco, M. G., Hulbert S. H., Trick H.N., and Pryor,A.J. (2003) Aberrant mRNA processing prevents functional transfer of the maize Rp1-D rust resistance gene to wheat and barley. Submitted.
- Zhao, B., Lin, X. Ardales, E., Trick, H., Leach, J., Hulbert, S.H. (2003) Maize Rxo1 and avrRxo1 from a rice bacterial pathogen interact to elicit a nonhost resistance reaction. Phytopathology Abstract.
- Bai, J., Pennill, L.A., Ning, J., Lee, S.W., Ramalingam, J., Webb C.A., Zhao, B., Sun, Q., Nelson, J.C., Leach J.E. and Hulbert S.H. (2002) Diversity in Nucleotide Binding Site-Leucine-Rich Repeat Genes in Cereals. Genome Research, 12:1871-1884
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Progress 12/01/00 to 11/30/02
Outputs
Major gene resistance to the bacterial leaf streak, caused by Xanthomonas oryzae pv. oryzicola (Xoo) has not been identified in rice. We identified a maize gene (Rxo1) that controls a hypersensitive resistance reaction to this pathogen in maize. We also identified a resistance gene-like (NBS-LRR) gene family that maps to the locus. We isolated the Avr gene that interacts with Rxo1 (avrRxo1) to facilitate cloning of the Rxo1 gene and enable the molecular characterization of the interaction. To accomplish this, an isolate of Xanthomonas oryzae pv. oryzae (the rice bacterial blight pathogen), which does not cause HR when infiltrated into maize, was used as a recipient for transformation of an Xoo cosmid library. A cosmid was identified which conferred the ability to cause the HR when infiltrated into the maize line B73 (Rxo1) but not Mo17 (rxo1). A gene with a 1.2 Kb coding region that conferred the ability to cause the HR was subcloned from the cosmid. When this gene
was placed under control of a plant promoter and bombarded into B73 (Rxo1) maize cells, it induced the HR as indicated by a lack of reporter gene expression. To determine if any of the linked NBS-LRR family members was the Rxo1 gene, the family members were characterized and used in transient assays to determine if they interact with the avrRxo1 gene. Three of five family members in the maize B73 line were predicted to code for potentially functional NBS-LRR proteins. One of these three appeared to account for most of the transcript from this gene family. This gene was also found to affect cell viability when co-bombarded into rxo1/rxo1 maize lines with the avrRxo1 gene, indicating the NBS-LRR gene is the Rxo1 gene. Similar transient assays indicated the Rxo1 gene also interacts with avrRxo1 and induces defense responses in rice cells. We are now transferring the putative Rxo1 gene to rice to determine if it will confer resistance to the bacterial leaf streak disease.
Impacts
Testing the utility of resistance gene transfer between cereals will have a big impact on designing strategies to develop disease resistant cultivars. The Rxo1 gene appears to be working in the heterologous cereal species, rice. If it controls the rice disease this will indicate isolation of pathogen resistance genes from nonhost cereal species is a viable strategy for engineering resistance.
Publications
- Zhao, B., Lin, X., Ardales, E.Y., Leach, J.E., Hulbert, S.H. (2002) A maize gene controlling a resistant reaction to rice bacterial streak. Proceedings of the International Rice Congress.
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Progress 01/01/01 to 12/31/01
Outputs
We have identified an NBS-LRR gene family with five members that map to the Rxo and Rpa genes. These are maize genes that control resistance reactions to bacterial pathogens of rice (Rxo) and sorghum (Rpa). We have cloned the avirulence gene from the rice pathogen (Xanthomonas oryzae pv. oryzicola) that the Rxo gene interacts with. We have used this gene to develop transient maize transformation assays to examine the NBS-LRR genes to determine which one controls the resistance reaction. We are now constructing maize transgenics that stably express this gene to verify it is the resistance gene. We are also transferring it to rice to determine if it can be used to control the rice bacterial streak disease.
Impacts
The transient assay system we developed will allow us to determine whether R genes will be expressed in heterologous cereals. We expect this to be an important tool in breeding cereals using recombinant DNA techniques.
Publications
- Zhao, B., Ardales, E.,Y., Leach, J., E., Hulbert, S.H. (2001) Non-host Avirulence gene avrRxo1 from Xanthomonal oryzae pv oryzicola confers the hypersensitive reaction on maize with Rxo1. Abstract. 10th International Congress on Molecular Plant-Microbe Interactions.
- Zhao, B., Lin X., Leach, J., Hulbert, S.H. (2001) Molecular analysis of maize genes conferring a non-host hypersensitive reaction to rice bacterial streak. Abstract. Proceedings Internat. Conf. Plant Genome, Plant Genome San Diego
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