Submitted to: Plant Signaling and Behavior
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2013
Publication Date: 12/31/2013
Publication URL: http://handle.nal.usda.gov/10113/59043
Citation: Cooper, B., Campbell, K., Mcmahon, M.B., Luster, D.G. 2013. Disruption of Rpp1-mediated soybean rust resistance by virus-induced gene silencing. Plant Signaling and Behavior. 8(12):e27543. Interpretive Summary: Phakopsora pachyrhizi, a fungus that causes rust disease on soybean, has potential to impart significant yield losses and disrupt food security and animal feed production. Rpp1 is a soybean gene that confers immunity to soybean rust, and it is important to understand how it regulates the soybean defense system and to use this knowledge to protect commercial crops. It was previously discovered that some soybean proteins resembling transcription factors accumulate in the nucleus of the cell of Rpp1 soybeans. To determine if they contribute to immunity, Bean pod mottle virus was used to attenuate or silence the expression of their genes. Rpp1 plants subjected to virus-induced gene silencing exhibited reduced amounts of RNA for five of the tested genes, and the plants developed rust-like symptoms after subsequent inoculation with fungal spores. Symptoms were associated with the accumulation of rust fungal RNA and protein. Silenced plants also had reduced amounts of RNA for the soybean Myb84 transcription factor and soybean isoflavone O-methyltransferase, both of which are important to phenylpropanoid biosynthesis and lignin formation, crucial components of rust resistance. These results help resolve some of the genes that contribute to Rpp1-mediated immunity and improve upon the knowledge of the soybean defense system. It is possible that these genes could be manipulated to enhance rust resistance in otherwise susceptible soybean cultivars.
Technical Abstract: Soybean rust is a fungus that causes disease on soybeans. The discovery of soybean genes and proteins that are important for disease resistance to soybean rust may help improve soybean cultivars through breeding or transgenic technology. Proteins previously discovered in the cell nucleus of soybeans resistant to soybean rust were thought to help activate resistance. So the genes for these proteins were manipulated with a plant virus to repress the amount of RNA and protein these genes make. When the originally resistant plants produced less RNA of the test genes as a result of the virus, the plants became susceptible to soybean rust. This meant that the test genes were important for disease resistance. An analysis of other genes also known to be important for disease resistance was performed, and it was found that when the virus reduced the amounts of RNA for the test genes, the RNA for some of the other disease resistance genes was reduced as well. This meant that these genes participate in a network of genes important for disease resistance, and this study showed that the disruption of one gene disrupts others in the network leading to loss of resistance. Two of the known genes that were disrupted in the network control the production of molecules that are toxic to fungi. Thus, soybean disease resistance is attributed in part to the production of antimicrobial molecules, and this research discovered several genes that control the production of these antimicrobial molecules. These data are most likely to influence scientists at universities, government agencies and companies who are searching for the soybean genes needed to fight rust diseases.