Pea aphid Acyrthosiphon pisum sequesters plant-derived secondary metabolite L-DOPA for wound healing and UVA resistance

Abstract

Herbivores can ingest and store plant-synthesized toxic compounds in their bodies, and sequester those compounds for their own benefits. The broad bean, Vicia faba L., contains a high quantity of L-DOPA (L-3,4-dihydroxyphenylalanine), which is toxic to many insects. However, the pea aphid, Acyrthosiphon pisum, can feed on V. faba normally, whereas many other aphid species could not. In this study, we investigated how A. pisum utilizes plant-derived L-DOPA for their own benefit. L-DOPA concentrations in V. faba and A. pisum were analyzed to prove L-DOPA sequestration. L-DOPA toxicity was bioassayed using an artificial diet containing high concentrations of L-DOPA. We found that A. pisum could effectively adapt and store L-DOPA, transmit it from one generation to the next. We also found that L-DOPA sequestration verity differed in different morphs of A. pisum. After analyzing the melanization efficiency in wounds, mortality and deformity of the aphids at different concentrations of L-DOPA under ultraviolet radiation (UVA 365.0 nm for 30 min), we found that A. pisum could enhance L-DOPA assimilation for wound healing and UVA-radiation protection. Therefore, we conclude that A. pisum could acquire L-DOPA and use it to prevent UVA damage. This study reveals a successful co-evolution between A. pisum and V. faba.

Figure 1

L-DOPA contents in Vicia faba and Trifolium repens (A) and L-DOPA (B) dopamine (C) contents in Acyrthosiphon pisum reared separately on V. faba and T. repens; L-DOPA concentrations in phloem of V. faba were detected and shown in (D) L-DOPA amounts in leaves of V. faba were extracted by grinding as a positive control; survival rate of aphids treated with L-DOPA (20 mM) by feeding artificial diets. Survival rate of A. pisim fed on T. repens (n_AD = 150, n_DOPA = 150) was shown in (E) Survival rate of A. pisim fed on V. faba (n_AD = 150, n_DOPA = 150) was shown in (F).

Figure 2. L-DOPA concentrations in different morphs of Acyrthosiphon pisum fed on two hosts, Vicia faba and Trifolium repens.

(A) L-DOPA concentrations; (B) Proportion of L-DOPA from each body part. Each value represents the mean ± SEM.

Figure 3

(A) Declining trend of L-DOPA concentrations after Acyrthosiphon pisum on Vicia faba were transferred into an artificial diet, and the last bar represents the L-DOPA concentrations in A. pisum fed on Trifolium Repens. (B) Relative transcript levels of TH from the aphids were reared on V. faba and the artificial diet; and (C) Relative transcript levels of TH from the aphids were reared on T. repens and the artificial diet. Each value represents the mean ± SEM.

Figure 4

(A) Difference in melanization efficiency of Acyrthosiphon pisum treated with L-DOPA and α- methyltyrosine; (B) Difference in melanization efficiency of A. pisum from Vicia faba and Trifolium repens; (C) L-DOPA contents from the aphids collected from two diets. Each value represents the mean ± SEM from independent determinations. (D) Wounds (pricking by glass needle) in melanization (arrows); (E) Eyes of embryos (arrow heads); (F) Color information (base on HSB, hue, saturation and brightness) in wound areas; and (G) Relative transcript level of proPO1 and proPO2 after treated by glass needle. Each value represents the mean ± SEM from independent determinations.

Figure 5

Melanization level in 48 hours difference of Acyrthosiphon pisum after 365 nm Ultraviolet radiation (UVA radiation), and (A) for Vicia faba, and (B) for Trifolium repens. (C) Mortality was assessed 3 days after UVA radiation. Each value represents the mean ± SEM from independent determinations.

Figure 6

(A) Dynamic L-DOAP concentration during UVA radiation and 72 hours after treatment; (B) Relative transcript levels of TH after UVA radiation treatment to Acyrthosiphon pisum from two hosts in 72 hours; (C) Relative transcript levels of proPO1; and (D) proPO2 after UVA radiation treatment to A. pisum from two hosts in 72 hours. Each value represents the mean ± SEM.

Figure 7

(A) Deformity-descendants laid by UV-treated mothers; (B) Deformity-descendants rate of Acyrthosiphon pisum from two hosts after UVA radiation treatment in 10 days.