Translating Knowledge Obtained from Arabidopsis to Engineer Broad Resistance in Soybean to Two Nematode Genera

Our understanding of plant pathways, signaling, and regulation involved in the plant resistance response to pathogens has been greatly enhanced through the study of Arabidopsis and its various mutants. We applied a portion of this knowledge from Arabidopsis to a crop plant, soybean, to confer resistance in soybean to the soybean cyst nematode (SCN: Heterodera glycines) and the root-knot nematode (RKN; Meloidogyne incognita). SCN is the major pathogen of soybean, and RKN is a highly destructive pathogen to a wide host range of plants, including soybean. We selected Arabidopsis and soybean genes from the literature to overexpress or silence. We transformed soybean roots with more than 50 DNA constructs to form composite plants. Each construct was designed to overexpress an Arabidopsis gene or soybean ortholog of an Arabidopsis gene, or to silence a soybean gene with the goal of conferring resistance to both SCN and RKN. Overexpression of genes encoding transcription factors GmRAP2.6 and GmWRKY70 decreased the number of mature females to less than 40% of the control. GmPAD1 and GmWIN3 decreased the number of nematodes to less than 50% of the control when overexpressed. Four Arabidopsis genes decreased the number of SCN cysts to less than 50% of those found on control roots when overexpressed, namely AtPAD4 (32%), AtNPR1(33%), AtAHBP (38%), and AtPR-5 (38%). Constructs targeted to silence soybean orthologs of known Arabidopsis genes important to pathogen defense also altered the number of SCN cysts. Silencing of GmCPR5, GmSGT1b, GmSSI1, and GmACD1, each reduced the number of SCN cysts more than 50%. However, silencing of GmEXP3 and GmDMR1 increased susceptibility as indicated by significant increases in the number of SCN cysts to 225% and 169% of the control value, respectively. The number of galls formed by RKN was also decreased 50% or more by overexpression of soybean genes encoding transcription factors GmRAP2.6 and GmWRKY70, PAD1-1, and by overexpression of Arabidopsis genes, including AtNDR1, AtNPR1, AtTGA2 AtEDS5, AtJAI1, AtEDS1, AtNHL1 and AtNHL8. Our results transfer knowledge gained from the model system, Arabidopsis, to soybean; they provide insights into the defense response of soybean to SCN; and they identify novel targets for controlling SCN and RKN.