Overexpression of α-SNAP_Rhg1 Can Improve rhg1-a-Mediated Soybean Resistance to Soybean Cyst Nematode

The rhg1-a and rhg1-b haplotypes of the soybean Rhg1 locus are economically effective tools for the control of soybean cyst nematode (SCN; Heterodera glycines), but ongoing SCN evolution requires improved sources of resistance. Both Rhg1 haplotypes carry multiple tandem repeat copies of a four-gene block encoding four disparate proteins, and resistance efficacy scales with copy number. The haplotypes encode different variants of an unusual α-SNAP protein whose abundance increases in the nematode-reprogrammed plant cells that form the syncytium (nematode feeding site), which subsequently collapses. The present study explored the simultaneous presence of two α-SNAP_Rhg1 protein types and elevation of α-SNAP_Rhg1 abundance, which were hypothesized to improve SCN resistance but are not achievable by conventional soybean breeding. We accomplished both via transgenic additions to an rhg1-a Rhg4 soybean line. Existing resistance to the HG type 0 and HG type 2.5.7 SCN was strengthened, measured as cyst production and final SCN egg counts, but resistance was not improved against an HG type 1.3.6.7 SCN population that was already highly virulent on the parent line. Greenhouse and field studies with a subset of lines showed no significant yield penalties. We conclude that cisgenic combination or elevated expression of the different α-SNAP genes may extend the efficacy and/or durability of Rhg1-mediated resistance. We also observed differential protein abundances for some α-SNAP_Rhg1 isoforms after inoculation with different HG type populations of SCN. The studies provide a foundation for further refinement of Rhg1-based SCN control. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.