Light Intensity-Mediated Induction of Trichome-Associated Allelochemicals Increases Resistance Against Thrips in Tomato

Abstract

In cultivated tomato (Solanum lycopersicum), increases in photosynthetically active radiation (PAR) induce type VI leaf glandular trichomes, which are important defensive structures against arthropod herbivores. Yet, how PAR affects the type VI trichome-associated leaf chemistry and its biological significance with respect to other photomorphogenic responses in this agronomically important plant species is unknown. We used the type VI trichome-deficient tomato mutant odorless-2 (od-2) and its wild type to investigate the influence of PAR on trichome-associated chemical defenses against thrips (Frankliniella occidentalis). High PAR increased thrips resistance in wild-type plants, but not in od-2. Furthermore, under high PAR, thrips preferred od-2 over the wild type. Both genotypes increased type VI trichome densities under high PAR. Wild-type plants, however, produced more trichome-associated allelochemicals, i.e. terpenes and phenolics, these being undetectable or barely altered in od-2. High PAR increased leaf number and thickness, and induced profound but similar metabolomic changes in wild-type and od-2 leaves. Enhanced PAR also increased levels of ABA in wild-type and od-2 plants, and of auxin in od-2, while the salicylic acid and jasmonate concentrations were unaltered. However, in both genotypes, high PAR induced the expression of jasmonic acid-responsive defense-related genes. Taken together, our results demonstrate that high PAR-mediated induction of trichome-associated chemical defenses plays a prominent role in tomato–thrips interactions.

Transcriptional variation in glucosinolate biosynthetic genes and inducible responses to aphid herbivory on field-grownArabidopsis thaliana

“…atra., P. xylostella, and F. occidentalis . Of these herbivores L. erysimi and F. occidentalis are sucking insects, while P. xylostella and Phyllotreta are leaf chewers (Ahuja 2010; Escobar-Bravo et al 2018). Lipaphis erysimi, P. xylostella, and Phyllotreta are specialists of Brassicaceae (Ahuja 2010), while F. occidentalis is a generalist, which feeds on various plant families (Escobar-Bravo et al 2018) (Figure 1b).…”

“…Recently, growing efforts have been made to understand how plants cope with complex field conditions (Kerwin et al 2015; Taylor et al 2017; Carrera et al 2017; Kono et al 2017; Sugiyama et al 2017; Hiraki et al 2018) and such in natura studies are important for the comprehensive understanding of gene functions from the laboratory to the field (Shimizu et al 2011; Kudoh 2016; Yamasaki et al 2018; Zaidem et al 2018; Nagano et al 2019). Insect herbivores are one of the most diverse organisms that impose biotic stresses on plants (Schoonhoven et al 2005; Ahuja 2010; Escobar-Bravo et al 2018). To deal with various threats, plants can activate defense mechanisms only when necessary.…”

A gain of function mutation in SlNRC4a enhances basal immunity resulting in broad-spectrum disease resistance

“…to an increase in trichome density, but causes upregulation of metabolites 65 or an increase in plant defense responses 66,67 which is sufficient to increase resistance. However, though several reports indicate that the amount of defensive metabolites produced is a function of the trichome head size [68][69][70] , as we report here, few works have related directly to the connection between trichome head size and pathogen resistance or plant defense pathways.…”

“…Upregulation or treatment with JA can increase the abundance of trichomes, both glandular and non-glandular, as well as activating plant defensive pathways, leading to increased pest and pathogen resistance 60 – 64 . In some cases, activation of JA dependent pathways does not lead to an increase in trichome density, but causes upregulation of metabolites 65 or an increase in plant defense responses 66 , 67 which is sufficient to increase resistance. However, though several reports indicate that the amount of defensive metabolites produced is a function of the trichome head size 68 – 70 , as we report here, few works have related directly to the connection between trichome head size and pathogen resistance or plant defense pathways.…”

Ultraviolet radiation modulates both constitutive and inducible plant defenses against thrips but is dose and plant genotype dependent

“…Fluctuations in light influence plant physiology, and plant adaptive responses to biotic stresses, modulating the plant interactions with herbivorous enemies. Both light quantity and quality have been shown to alter plant constitutive and inducible defenses against arthropod herbivores (Escobar-Bravo et al 2018, 2019a. In particular, variation in ultraviolet radiation (λ 290-400 nm) levels, a relatively small component of the solar light spectrum reaching the terrestrial ecosystems, has been reported to affect plant protection against herbivory (Ballaré 2014).…”