Current understanding of maize and rice defense against insect herbivores
Jinfeng Qi et al.

Plants have sophisticated defense systems to fend off insect herbivores. How plants defend against herbivores in dicotyledonous plants, such as Arabidopsis and tobacco, have been relatively well studied, yet little is known about the defense responses in monocotyledons. Here, we review the current understanding of rice (Oryza sativa) and maize (Zea mays) defense against insects. In rice and maize, elicitors derived from insect herbivore oral secretions or oviposition fluids activate phytohormone signaling, and transcriptomic changes mediated mainly by transcription factors lead to accumulation of defense-related secondary metabolites. Direct defenses, such as trypsin protein inhibitors in rice and benzoxazinoids in maize, have anti-digestive or toxic effects on insect herbivores. Herbivory-induced plant volatiles, such as terpenes, are indirect defenses, which attract the natural enemies of herbivores. R gene-mediated defenses against herbivores are also discussed.

 A working model of defense responses in an herbivore-attacked plant. (A) Herbivore-derived elicitors are perceived by unidentified receptors on the plasma membranes, triggering rapid activation of MAPKs followed by biosynthesis of phytohormones, JA, JA-Ile, and ethylene. After several steps of signaling transduction, transcription factors (MYC2 and ERFs, for instance) regulate the accumulation of non-volatile secondary metabolites (such as TPIs in rice and BXs in maize), which function as direct defenses against herbivores. (B) Herbivory-induced plant volatiles recruit natural enemies above ground (such as parasitic wasps) and below ground (entomopathogenic nematodes, for instance) to indirectly defend plants against herbivores. Solid lines indicate reported pathways in monocots, dashed lines indicate unconfirmed pathways inferred from findings in dicots.

https://www.sciencedirect.com/science/article/pii/S2468265918300696

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