Engineering a host defense regulatory gene, phytoalexin DEFICIENT4 (PAD4), for enhancing resistance to soybean aphid

Soybean (Glycine max) is important for both its use in agriculture and industrial applications. Soybean plants must withstand many biological stresses, including viral and pathogenic infections, and nematodes among other pests. Soybean aphids (Aphis glycines Matsumura) alone can cause decreases in both yield and seed quality. Current management strategies involve extensive scouting and application of expensive insecticides. Although these strategies reduce the threat, they do not completely eliminate soybean aphid as a pest. As a complement to current management practices, biotechnological approaches to enhance plant immunity via the genetic manipulation of components of the plant’s own defense signaling pathways offers an attractive strategy for boosting plant defenses. A defense regulatory gene PHYTOALEXIN DEFICINT4 (PAD4) is an attractive candidate for over-expression in soybean plants due to its important role in plant defenses against a broad-spectrum of pathogens. The objectives of our study were to: (1) determine the role of PAD4 in soybean-soybean aphid interaction and (2) develop transgenic soybean plants that over-express the PAD4 gene. The expression of PAD4 in soybean plants that contain the Rag1 resistance gene was monitored via real-time quantitative polymerase chain-reaction in a time course experiment. The resistant cultivar displays elevated levels of PAD4 as compared to the susceptible control. Furthermore, the PAD4 transcripts are induced to higher levels within 24 h of aphid feeding. Transgenic soybean lines expressing soybean PAD4 from a soybean ubiquitin promoter are currently being generated (T0 generation) and will be evaluated for their response to soybean aphid infestation. The outcome of this research will lead to a better understanding of the role PAD4 plays in aphid resistance and allow for the development of transgenic lines with heightened resistance to soybean aphid.