Deciphering the role of first line of defenses in sorghum against sugarcane aphids

Sorghum (Sorghum bicolor (L.) Moench) is ranked among the important cereal crops for providing food, nutritional and biomass security worldwide. However, insect pests continue to inflict damage to sorghum plants. Sugarcane aphid (SCA) Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) is an  invasive pest on sorghum in the United States, which ravenously feeds on plant sap  and drains the nutrients, thereby impacting plant’s health and yield. Use of resistant varieties is a safer and potential way of preventing plant damage caused by insect pests. Previously, we identified varied levels of resistance to SCA in founder lines of the sorghum NAM population. Compared to wild-type plants, SCA proliferation was lower on SC265 and higher on SC1345 plants. In this study, we utilized RNA-seq to identify the genes encoding for signal transduction and metabolic pathways involved in providing defenses to SCA. Co-expression network analysis demonstrate that  aphid feeding at early time points modulate the genes related to innate systemic resistance, phytohormones, and phenylpropanoid metabolism in the aphid resistant sorghum line. Specifically,  the genes related to leucine-rich repeat (LRR), leucine rich receptor like proteins and disease resistance-responsive (dirigent-like protein) were highly upregulated in the aphid resistant sorghum line, but not in the susceptible line. Collectively, our results suggest that the aphid resistant sorghum line is better adapted to activate early defense signaling mechanisms to curb SCA infestation.