Combined Transcriptome and Metabolome Analysis of Alfalfa Responses to Aphid Infestation

Alfalfa (Medicago sativa L.) is an economically important forage legume. As a result of the extensive and intensive cultivation of alfalfa planting and the gradual expansion of planting areas, pest occurrence has increased in frequency. Aphids are one of the main pests that threaten the growth and productivity of alfalfa. After an aphid outbreak, alfalfa yield and quality are commonly greatly reduced. At present, there are few studies on alfalfa plants infested with aphids, so it is imperative to study the regulatory mechanisms of aphid infestation tolerance in alfalfa. In this study, alfalfa plants from the variety “Wudi” were investigated, and pea aphids were selected for inoculation. The transcriptome and metabolome data were analyzed at three time points (0 d, 1 d, and 4 d), revealing 3458 differentially expressed genes and 358 differential metabolites. Trend analysis of DEGs and DAMs revealed that the former were significantly enriched in three distinct trends, whereas the latter were significantly enriched in only one. Moreover, 117 important hub genes associated with alfalfa response to aphid infestation were screened by WGCNA. By mapping DEGs and DAMs to KEGG pathways, it was found that the “phenylpropanoid biosynthesis”, “flavonoid biosynthesis”, and “isoflavonoid biosynthesis” pathways play an important role in alfalfa responses to aphid infestation. These results further elucidate the regulatory mechanism of alfalfa in response to aphid infestation and provide valuable information for breeding new aphid-resistant plant varieties.