Influence of phloem lectin CsPP2-A1 on aphid development via mediation of phenylpropanoid and flavonoid biosynthesis in cucumber.

Background: Aphid, Aphis gossypii Glover, is a pest that significantly affects cucumbers (Cucumis sativus L.). Phloem protein 2 (PP2) is a conserved phloem lectin. Our previous study showed that the expression of CsPP2-A1 under aphid attack affected the accumulation of flavonoids and total phenolics in cucumber. The novel mechanism of lectin CsPP2-A1 mediating secondary metabolites affecting aphid resistance in cucumbers needs to be investigated.

Results: The weight and length of aphids on CsPP2-A1 overexpression (CsPP2-A1-OE) cucumber plants significantly reduced compared to wild-type (WT). Conversely, aphids on CsPP2-A1 RNA interference (CsPP2-A1-RNAi) plants showed the opposite trend. Using secondary metabolomics, small molecular weight secondary metabolites were qualitatively and quantitatively assessed in WT and transgenic cucumber plants after aphid inoculation. The overexpression of CsPP2-A1 resulted in the up-regulation of differential metabolites (DMs) in phenylpropanoid biosynthesis, whereas interference expression of CsPP2-A1 led to a down-regulation of DMs in the flavonoid biosynthesis. Concurrently, it was observed that the CAD activity and the expression of the CsPAL, and CsCAD in OE-2 were up-regulated significantly. A significant reduction in the activities of CHI, F3H, and the expression of CsF3H, CsCHS, CsFLS, and CsCCR was noted in RNAi-2.

Conclusion: CsPP2-A1 indirectly affects the growth and development of aphids via mediation of phenylpropanoid and flavonoid biosynthesis. The indirect effects of the interaction of CsPP2-A1 with aphids offer insights into plant-insect interaction studies. © 2025 Society of Chemical Industry.