Salivary effectors Fomyr6 and Foαglu1 facilitate Frankliniella occidentalis in overcoming the defense of kidney bean plant.

BACKGROUND

Frankliniella occidentalis (western flower thrips, WFT), a highly destructive polyphagous pest, has evolved sophisticated mechanisms to overcome plant defenses. Salivary effectors play a crucial role in this process. In this study, we investigated the promotion effects of two candidate effectors (Fomyr6 and Foαglu1) previously identified in F. occidentalis salivary glands on the adaptation of F. occidentalis to host plant. First, we determined their subcellular localization, then expressed these proteins in kidney bean plants using an Agrobacterium-mediated transient expression system. We further analyzed their impact on plant defense responses and the WFT feeding behavior.

RESULTS

Both Foαglu1 and Fomyr6 were successfully expressed in kidney bean leaves 72 h after Agrobacterium tumefaciens infection and were predominantly localized to the plasma membrane in Nicotiana benthamiana. Overexpression of both effectors suppressed the activity of key defense-related enzymes, including allene oxide synthase (AOS), lipoxygenase (LOX), and phenylalanine ammonia-lyase (PAL). Additionally, they significantly down-regulated salicylic acid (SA) and jasmonic acid (JA) levels. Strikingly, while both Fomyr6 and Foαglu1 enhanced lignification, they concurrently suppressed chemical defenses, as evidenced by reduced accumulation of total phenolics and flavonoids. Behavioral assays further revealed that F. occidentalis exhibited improved performance on effector-expressing kidney bean plants, with increased oviposition and larger feeding damage areas.

CONCLUSION

Our findings strongly suggest that Fomyr6 and Foαglu1 act as salivary effectors that enhance WFT feeding and reproduction by suppressing plant defenses. This includes modulating the activity of defense-related enzymes, disrupting secondary metabolite biosynthesis, and altering phytohormone signaling pathways. © 2025 Society of Chemical Industry.