Transcriptional responses of tolerant and susceptible soybeans to soybean aphid (<i>Aphis glycines</i> Matsumura) herbivory

The soybean aphid, Aphis glycines Matsumura, was introduced in 2000 to North America and has become one of the most significant pests to soybean, Glycine max (L.) Merrill, production. Possible solutions to this problem are the use of resistant plants and the understanding of the genes involved in plant resistance. In this study, we sought to better understand the genes involved in the tolerance response of soybean plants to the soybean aphid, utilizing tolerant (KS4202) and susceptible (K-03-4686) plants. Studies were conducted under greenhouse conditions. Leaf samples of both tolerant and susceptible plants were collected at day 5 and day 15 after infestation and analyzed by sequencing-by-synthesis on an Illumina GA II X instrument. In the tolerant genotype, 3 and 36 genes were found to be differentially expressed in the infested plants compared to the control treatments at day 5 and day 15, respectively. A similar comparison in the susceptible genotype revealed 0 and 11 genes to be differentially expressed at day 5 and day 15, respectively. Predominately, genes related to plant defense, such as WRKY transcription factors, peroxidases, and cytochrome p450s, were upregulated in the tolerant genotype 15 days post-infestation by aphids. In contrast, none of these genes were similarly up-regulated in the susceptible plants, suggesting that consistent elevation of defense responses is important to plant tolerance. However, significant genotypic differences in global gene expression were also found when transcriptomes from control uninfested plants were compared at both day 5 and 15. qPCR validation of select genes confirmed our RNA-seq data. These comparisons indicate that potentially broader regulation of transcriptomes also contributes to the tolerance response and provides data that the tolerant genotype (KS4202) could be useful in soybean breeding programs trying to minimize production losses accruing from soybean aphid feeding.