Project Number: 8042-21220-232-000-D
Project Type: In-House Appropriated
Start Date: Jul 30, 2013
End Date: Mar 27, 2018
The long-term objective is to develop soybean with resistance to pests and pathogens. Soybean is the second largest crop in the United States with a farm value of $30 billion in 2009. A number of diseases affect soybean yield, but by far the greatest loss is due to soybean cyst nematode(SCN), Heterodera glycines. While nematodes are a long-standing problem, the greatest emerging threat to the US soybean crop is soybean rust (SBR), a disease caused by the fungus Phakopsora pachyrhizi. Gene expression will be examined in the SCN-induced syncytium (multinucleated cell) to determine if gene expression and protein targeting is asymmetric across the length of the syncytium (i.e., polarized). New candidate genes responsible for susceptibility and resistance to SCN and SBR will be identified and their functions investigated. Transgenic and mutagenized soybean plants will be examined to determine if there are unintended changes in the proteome. The specific objectives of the proposal are: Objective 1: Discover and characterize plant and pathogen genes and molecular signals important for resistance or pathogenicity at the molecular level with emphasis on soybean interactions with soybean rust and soybean cyst nematode. Objective 2: Identify genes expressed during interactions of soybean with nematodes and fungi at various intervals on resistant and susceptible plants, and develop transformed plants with over-expressed and silenced genes to improve resistance to nematodes and fungi. Sub-Objective 2A. Identify genes expressed by the host and pathogen during a resistant and susceptible interaction of soybean with SCN and SBR. This will provide insights into host-pathogen interactions and will identify candidate genes for testing. Sub-Objective 2B. Overexpress and silence candidate genes in transformed soybean plants and soybean roots to determine their effect on pathogen growth and development. Objective 3: Determine the collateral variation in seed composition between crop plants developed using genetic engineering, mutagenesis and classical breeding.
Plant hormonal signal pathways (e.g. ethylene, auxin, IDA), will be examined to determine how they contribute to growth of the feeding structure (syncytium) for SCN. Fluorescent markers will be used to identify expression patterns for genes and proteins involved in auxin, ethylene and IDA synthesis, transport and signaling to determine their interactive roles in the asymmetric growth of the syncytium. A novel IDA-like gene discovered in root-knot nematodes will be assayed for its role in nematode growth within the plant by overexpression of the nematode IDA in the plant roots and suppression of the IDA in the nematode by RNAi gene silencing. Fifteen proteins that accumulate in the nucleus at a higher level and 52 proteins that accumulate at a lower level in Rpp1 plants resistant to SBR will be examined. Using virus-induced gene silencing and virus-induced over-expression, it will be tested whether altered levels of these proteins contribute to Rpp1 resistance and whether these genes can be used to improve resistance. Roots infected with SCN will be examined using Illumina RNA-seq. DNA constructs representing genes of interest will be transformed into soybean roots and challenged with SCN to determine if they contribute to resistance or susceptibility. The seed proteins and their abundance in soybean lines derived via conventional plant breeding, mutagenesis, and genetic engineering and soybean landraces and wild soybean from which they are derived will be compared using 2-dimensional electrophoresis, mass spectrometry, and other techniques.