Identification and Functional Analysis of Candidate Effectors in the Sorghum Aphid, Melanaphis sorghi

The sorghum aphid (Melanaphis sorghi), a phloem-feeding insect pest, causes severe economic losses in sorghum-producing regions worldwide. During feeding, aphids secrete salivary proteins with potential effector functions that play pivotal roles in plant-insect interactions. However, relatively few secreted proteins and effectors have been characterized in M. sorghi. In this study, proteomic analysis of aphid-infested sorghum leaves identified 69 putative aphid-derived proteins. Bioinformatic analyses were subsequently used to predict signal peptides within these proteins. Among the five candidates with signal peptides, MsSP1 was further confirmed to be delivered into sorghum tissues during aphid feeding by immunoblotting using a specific anti-MsSP1 antibody. Functional characterization revealed that silencing the MsSP1 gene in aphids by RNAi interference significantly reduced aphid fitness on sorghum. Moreover, transient expression of MsSP1 in Nicotiana benthamiana suppressed cryptogein-induced cell death and hydrogen peroxide accumulation, indicating that MsSP1 interferes with plant immune responses. Collectively, these results suggest that MsSP1 may act as a virulence effector that enhances aphid performance while suppressing host defense. This study expands current knowledge of plant-aphid interactions and provides new insights that may facilitate the development of sustainable pest-management strategies.