Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2010
Publication Date: 2/11/2011
Citation: Pandey, A.K., Yang, C., Zhang, C., Graham, M.A., Horstman, H.D., Lee, Y., Zabotina, O.A., Hill, J.H., Pedley, K.F., Whitham, S.A. 2011. Functional analysis of the Asian soybean rust resistance pathway mediated by Rpp2. Molecular Plant-Microbe Interactions. Molecular Plant-Microbe Interactions. 24:194-206. Interpretive Summary: Asian soybean rust (ASR) is an aggressive disease caused by a fungus that posses a major risk to U.S. soybean production. Currently, all of the elite soybean cultivars grown in the U.S. and abroad are vulnerable to the disease. On susceptible soybean plants, the pathogen penetrates and colonizes the host leaf tissue resulting in tan-colored lesions on the leaf surface and the development of numerous spores. Despite large-scale screening efforts, few genes that confer resistance to the pathogen have been identified. One of the genes found to confer resistance is Rpp2. Rpp2-mediated resistance limits the growth of the fungus. The response is characterized by the formation of reddish-brown lesions with few spores produced. The Rpp2 gene product is thought to play a role in the recognition of the pathogen, and little is known about the other genes required for its function. Using a loss-of-function approach to discern gene function, we screened 140 candidate genes to identify those that are required for Rpp2-mediated resistance. Candidate genes tested included known defense-related genes identified in other infections. We identified 11 genes that comprised Rpp2-mediated resistance when disrupted. Together, our results provide new insight into the genetics, signaling, and biochemical pathways required for resistance and will assist in the development of ARS resistant soybean cultivars.
Technical Abstract: Asian soybean rust (ASR) is an aggressive foliar disease caused by the obligate biotrophic fungus Phakopsora pachyrhizi. On susceptible plants, the pathogen penetrates and colonizes host leaf tissue resulting in the formation of necrotic lesions and the development of numerous uredinia. The soybean Rpp2 gene confers resistance to specific isolates of P. pachyrhizi. Rpp2-mediated resistance limits the growth of the pathogen and is characterized by the formation of reddish-brown lesions and few uredinia. Using virus-induced gene silencing, we screened 140 candidate genes to identify those that play a role in Rpp2 resisance towards P. pachyrhizi. Candidate genes included putative orthologs to known defense signaling genes, transcription factors, and genes previously found to be up regulated during the Rpp2 resistance response. We identified 11 genes that compromised Rpp2-mediated resistance when silenced, including GmEDS1, GmNPR1, GmPAD4, GmPAL1, five predicted transcription factors, an O-methyl transferase, and a cytochrome P450 monooxygenase. Together, our results provide a new insight into the signaling and biochemical pathways required for resistance against P. pachyrhizi.