Soybean cyst nematode (SCN) is the most yield-reducing pathogen of U.S. soybeans. We will describe new discoveries about the mechanisms of soybean resistance to SCN. Soybean breeders rely heavily on the complex Rhg1 locus. We previously reported that one of the Rhg1 genes encodes an atypical, cytotoxic α-SNAP protein that disrupts host cell vesicle trafficking. α-SNAP and NSF are essential eukaryotic housekeeping proteins that normally interact to sustain vesicular trafficking. We more recently learned that 100% of soybean lines with Rhg1 carry, at an unlinked locus, the gene for an NSF protein with unusual amino acids at the predicted α-SNAP/NSF interaction site. This NSF-RAN07 exhibits better interaction with Rhg1 α-SNAPs and partially mitigates their cytotoxicity. Separately, we learned that Rhg1-mediated resistance can involve depletion of wild-type α-SNAP abundance. In unpublished work, we will report that the responsible gene at another SCN resistance QTL encodes a gamma-SNAP protein. Hence for disease resistance, SCN selection pressure has apparently driven multiple types of convergent re-wiring of soybean expression of NSF and SNAP proteins, which in other organisms are thought to be conserved and relatively invariant components of the SNARE recycling machinery. We will also present findings that transgenic transfer of this cyst nematode resistance can function in other plant species against other cyst nematodes. Lastly, we will share findings that a second functional Rhg1 protein product (the Rhg1 amino acid permease-like protein) is upregulated at stages of the infection process that differ from the primary site of the Rhg1 α-SNAP abundance increases, and that the Rhg1 amino acid permease-like protein interacts with unique protein partners. The findings indicate that Rhg1 is a resistance pyramid that encodes more than one distinct mode of action.
Coauthors: Shaojie Han – University of Wisconsin - Madison;Adam Bayless – Colorado State University;Katelyn Butler – Anderson University;Ryan Zapotocny – University of Wisconsin - Madison;John Smith – University of Wisconsin - Madison;Christina Fliege – University of Illinois at Urbana-Champaign;Matthew Hudson – University of Illinois at Urbana-Champaign;Brian Diers – University of Illinois at Urbana-Champaign;Shiyan Chen – Cornell University;Xiaohong Wang – USDA-ARS and Cornell University;Derrick Grunwald – University of Wisconsin - Madison