Abscisic Acid: A Potential Secreted Effector Synthesized by Phytophagous Insects for Host-Plant Manipulation

Abstract

Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety of plant processes, including facets of growth and development as well as responses to abiotic and biotic stress. ABA had previously been reported in a wide variety of animals, including insects and humans. We used high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-(ESI)-MS/MS) to examine concentrations of ABA in 17 species of phytophagous insects, including gall- and non-gall-inducing species from all insect orders with species known to induce plant galls: Thysanoptera, Hemiptera, Lepidoptera, Coleoptera, Diptera, and Hymenoptera. We found ABA in insect species in all six orders, in both gall-inducing and non-gall-inducing species, with no tendency for gall-inducing insects to have higher concentrations. The concentrations of ABA in insects often markedly exceeded those typically found in plants, suggesting it is highly improbable that insects obtain all their ABA from their host plant via consumption and sequestration. As a follow-up, we used immunohistochemistry to determine that ABA localizes to the salivary glands in the larvae of the gall-inducing Eurosta solidaginis (Diptera: Tephritidae). The high concentrations of ABA, combined with its localization to salivary glands, suggest that insects are synthesizing and secreting ABA to manipulate their host plants. The pervasiveness of ABA among both gall- and non-gall-inducing insects and our current knowledge of the role of ABA in plant processes suggest that insects are using ABA to manipulate source-sink mechanisms of nutrient allocation or to suppress host-plant defenses. ABA joins the triumvirate of phytohormones, along with cytokinins (CKs) and indole-3-acetic acid (IAA), that are abundant, widespread, and localized to glandular organs in insects and used to manipulate host plants.

Plant-animal below-ground interaction modifies plant phenotype and its above-ground interaction: a review and new case study

“…In general, root damage stimulates defense signaling responses that are different from those activated in above-ground host organs (Acosta et al 2013;Johnson et al 2016). Recent studies have documented the secretion of abscisic acid by larvae of gall-inducing insects for host plant manipulation, as this compound has significant consequences on plant growth and survival (Seng et al 2023). Specifically, plants respond to root damage mainly by producing jasmonate (Lu et al 2015), a plant hormone that triggers physiological cascades that can indirectly modulate other plant interactions, in addition to providing resistance against plant attackers (Toby Kiers et al 2010;Lu et al 2015).…”

Harnessing Phytohormones: Advancing Plant Growth and Defence Strategies for Sustainable Agriculture

“…ABA primes JA‐regulated defence responses upon secondary herbivore attack, enhancing plant resistance against insects like Pieris rapae (Vos et al, 2013, 2019). However, recent findings suggest that insects exploit ABA to manipulate nutrient allocation mechanisms or suppress host‐plant defences (Seng et al, 2023). Mutants impaired in ABA synthesis, such as aba2‐1 , exhibit increased weight gain of herbivorous larvae like Spodoptera littoralis and altered feeding behaviour, highlighting the crucial role of ABA in regulating plant‐insect interactions (Thaler and Bostock, 2004; Christmann et al, 2006).…”