Soybean defense responses to the soybean aphid (Aphis glycines)

The United States is the world’s largest producer of soybean, Glycine max (L.) Merr., worldwide, producing 32.3% of 283 million metric tons in 2014.  However, crop loss from the soybean aphid, Aphis glycines Matsumura, has resulted in reductions in soybean yield as high as 40%. PHYTOALEXIN DEFICIENT4 (PAD4), a defense regulatory gene, has been documented to be directly involved in the defense response to both aphids and pathogens in the model system Arabidopsis thaliana. Expression levels of PAD4 and two peroxidase genes (PRX1 and PRX2) were measured in resistant (antibiotic – RAG2 and tolerant – KS4202) and susceptible cultivars of soybean in response to soybean aphid herbivory. Differential expression of these three defense-related genes was documented for each cultivar/category of resistance (antibiosis and tolerance). Our results suggest that PAD4 may play a potential role in RAG2 soybean mediated resistance to the soybean aphid. Additionally, one of the peroxidase genes, PRX1, was significantly up-regulated in the tolerant soybean cultivar KS4202.