|Van De Mortel, Marijn|
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2007
Publication Date: 8/1/2007
Citation: Van De Mortel, M., Recknor, J.C., Graham, M.A., Nettleton, D., Dittman, J., Nelson, R., Godoy, C.V., Abdelnoor, R.V., Almeida, A.M., Baum, T.J., Whitham, S.A. 2007. Biphasic responses of resistant and susceptible soybean plants to soybean rust, Phakopsora pachyrhizi. Molecular Plant-Microbe Interactions. 20:887-899. Interpretive Summary: Soybean rust is a fungal disease capable of causing up to 80% yield loss. It has recently spread to all major soybean-producing countries including the United States. Thus far, only a few soybean genes have been identified that provide resistance to soybean rust. However, the mechanisms behind resistance are poorly understood. The research described here identifies genes that are controlled by the Rpp2 soybean rust resistance gene. Upon infection with soybean rust, some of these genes are turned on while others are turned off. Plants lacking the Rpp2 gene are not able to regulate these genes in the same way. Therefore, Rpp2 recognizes that the plant is being attacked and regulates the plant defense response. Besides controlling soybean rust, these genes may be used by researchers and breeders to defend against other plant pathogens.
Technical Abstract: Soybean rust (SBR), caused by Phakopsora pachyrhizi, is now established in all major soybean-producing countries. There is currently little information on the molecular basis of P. pachyrhizi-soybean interactions, which will be needed to assist future efforts to develop effective resistance. Toward this end, the abundance of soybean mRNA transcripts was measured over a seven-day SBR-infection time course using the Affymetrix GeneChip' Soybean Genome Array in the SBR-resistant accession PI230970 carrying the Rpp2 resistance gene and the highly susceptible genotype Embrapa-48. The expression profiles of differentially expressed genes (compared to non-infected mock expression levels) revealed stage-specific responses to SBR in both genotypes. In each, differential gene expression occurred within the first 12 hrs, which corresponds to fungal germination and penetration of the epidermal cells. Most of these genes then returned to mock levels by 24 hrs and remained low in the susceptible genotype until 96 hrs when rapid fungal growth began. Gene expression in the resistant genotype diverged from the mock earlier at 72 hrs, demonstrating that Rpp2-mediated defenses were initiated at or just prior to this time. These data suggest that SBR initially induces a non-specific response that is suppressed when early steps in colonization are completed in both plant types. Rpp2 mediates induction of soybean defenses later, but prior to the onset of rapid fungal growth that occurs in the susceptible genotype.