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Research advances in plant–insect molecular interaction

Chun-Yu Chen, Ying-Bo Mao*

Abstract Acute and precise signal perception and transduction are essential for plant defense against insects. Insect elicitors—that is, the biologically active molecules from insects’ oral secretion (which contains regurgitant and saliva), frass, ovipositional fluids, and the endosymbionts—are recognized by plants and subsequently induce a local or systematic defense response. On the other hand, insects secrete various types of effectors to interfere with plant defense at multiple levels for better adaptation. Jasmonate is a main regulator involved in plant defense against insects and integrates with multiple pathways to make up the intricate defense network. Jasmonate signaling is strictly regulated in plants to avoid the hypersensitive defense response and seems to be vulnerable to assault by insect effectors at the same time. Here, we summarize recently identified elicitors, effectors, and their target proteins in plants and discuss their underlying molecular mechanisms.

Figure 1

Figure 1. Schematic diagram of herbivory-associated elicitors and effectors manipulating plant defense. Receptors (SYR, PEPR, INR, and LecRKs) located on the plant cell surface recognize small peptides (sytemine, inceptin, and Peps) and, together with the co-receptors (SERKs/BAK1 and SOBIR1), trigger downstream defense signaling. Also, elicitors derived from insects, including FACs, β-Glu, and GOX, are able to activate plant defense with the unknown mechanisms. On the other hand, insects secrete effectors to weaken plant defenses. Some effectors interfere with jasmonate (JA) signaling directly (HARP1, 2b, C2, βC1, and SSGP-71) or indirectly (Armet and Bt56) by enhancing salicylic acid (SA) accumulation to compromise JA signaling. Some effectors (Mp1 and Me10) target plant proteins (VPS52 and TFT7) that are directly involved in defense. The DNase II eliminates the extracellular DNA which is released by damaged cells to trigger plant defense. MIF and C002 from aphids are of benefit to insects living on the host plants, but the underlying mechanisms remain elusive. Notably, some elicitors/effectors are plant-specific. Here, the GOX from Helicoverpa zea acts as an effector, inhibiting nicotine accumulation in tobacco, and, on the other hand, acts as an elicitor specifically inducing plant response in tomato.