An atypical N-ethylmaleimide sensitive factor enables the viability of nematode-resistant <i>Rhg1</i> soybeans

Abstract

N-ethylmaleimide sensitive factor (NSF) and α-soluble NSF attachment protein (α-SNAP) are essential eukaryotic housekeeping proteins that cooperatively function to sustain vesicular trafficking. The "resistance to <i>Heterodera glycines</i> 1" (<i>Rhg1</i>) locus of soybean (<i>Glycine max</i>) confers resistance to soybean cyst nematode, a highly damaging soybean pest. <i>Rhg1</i> loci encode repeat copies of atypical α-SNAP proteins that are defective in promoting NSF function and are cytotoxic in certain contexts. Here, we discovered an unusual <i>NSF</i> allele (<i>Rhg1</i>-associated NSF on chromosome 07; <i>NSF</i>_<i>RAN07</i> ) in <i>Rhg1</i>⁺ germplasm. NSF_RAN07 protein modeling to mammalian NSF/α-SNAP complex structures indicated that at least three of the five NSF_RAN07 polymorphisms reside adjacent to the α-SNAP binding interface. NSF_RAN07 exhibited stronger in vitro binding with <i>Rhg1</i> resistance-type α-SNAPs. NSF_RAN07 coexpression <i>in planta</i> was more protective against <i>Rhg1</i> α-SNAP cytotoxicity, relative to WT NSF_Ch07 Investigation of a previously reported segregation distortion between chromosome 18 <i>Rhg1</i> and a chromosome 07 interval now known to contain the <i>Glyma.07G195900</i> NSF gene revealed 100% coinheritance of the <i>NSF_RAN07</i> allele with disease resistance <i>Rhg1</i> alleles, across 855 soybean accessions and in all examined <i>Rhg1</i>^<i>+</i> progeny from biparental crosses. Additionally, we show that some <i>Rhg1</i>-mediated resistance is associated with depletion of WT α-SNAP abundance via selective loss of WT α-SNAP loci. Hence atypical coevolution of the soybean SNARE-recycling machinery has balanced the acquisition of an otherwise disruptive housekeeping protein, enabling a valuable disease resistance trait. Our findings further indicate that successful engineering of <i>Rhg1</i>-related resistance in plants will require a compatible NSF partner for the resistance-conferring α-SNAP.