Fortifying crop defenses: unraveling the molecular arsenal against aphids

Aphids cause enormous financial losses to various crop plants on a global scale. Moreover, aphids are vectors for many plant viral diseases that can further hasten crop yield losses. Aphids secrete saliva during feeding that contains effectors that can regulate plants' defense responses and their underlying mechanisms. Although much research has been undertaken to determine the mechanisms contributing to plant-aphid interactions, our understanding of defense mechanisms against aphids is insufficient. The presence of piercing-sucking mouthparts in aphids makes the identification of aphid resistance more challenging, hindering our understanding of the mechanisms of plant resistance to aphids. In this article, we consolidate and assess the evidence that is currently available on plant-aphid interactions, address the gaps in our understanding, and propose new research directions. As an outcome, we present an in-depth review of the molecular mechanisms of aphid resistance in crops from five perspectives: physical protection against aphids using volatile compounds, PAMP-triggered immunity (PTI), effector-triggered immunity (ETI), plant hormone signaling and the inheritance of induced resistance through epigenetics.