Advances in molecular interactions between rice and insect herbivores

To adapt to each other, plants and insect herbivores have developed sophisticated molecular interactions. Here, we summarize current knowledge about such molecular interactions between rice, a globally important food crop, and insect herbivores. When infested by insect herbivores, rice perceives herbivore- and/or damage-associated molecular patterns (HAMPs/DAMPs) via receptors that activate early signaling events such as the influx of Ca²⁺, the burst of reactive oxygen species, and the activation of MPK cascades. These changes result in specific rice defenses via signaling networks that mainly include phytohormones (jasmonic acid, salicylic acid, ethylene, and abscisic acid) and transcription factors. Some compounds, including flavonoids, phenolamides, defensive proteins, and herbivore-induced rice volatiles, have been reported to be used by rice against insects. Insect herbivores can deliver effectors or factors to inhibit rice defenses or enhance rice susceptibility. Although the number of HAMPs and defense-suppressing effectors from rice piercing-sucking insects has increased rapidly, none from rice chewing insects has been identified. Moreover, herbivore effectors or factors that induce rice susceptibility, and rice immune receptors recognizing HAMPs or effectors, are not well characterized. We point out future research directions in this area and highlight the importance of elucidating the mechanisms for rice sensing of insect herbivores and for insect counter-defenses against plants.