Plant Defences against Herbivore Attack

Abstract

Different from animals, plants can usually not run away from their attackers, such as herbivores, and have thus evolved a diverse arsenal of defences. These defences can be constitutive or inducible, they can be directly affecting the attacker or be mediated by a third organism (indirect defence) and span from physical structures, such as thorns, and reinforced cell walls to chemical defences (plant secondary metabolites) with toxic, antidigestive and antinutritive mechanisms of action. Plant secondary metabolite production is characterised by a very high diversity within and between compound classes, high functional redundancy, and multifunctionality. Moreover, they do not only mediate direct defensive functions by poisoning their attackers, but are the language with which information is transferred between organisms and that meditates complex interactions within the plants' associated communities. Biotechnological, plant breeding and biological control approaches can use the power of natural plant defences to control pests in agriculture, sustainably. Key Concepts Plants employ various direct and indirect mechanisms to defend against herbivores. Direct defences include chemical defences and physical defences. Plant secondary metabolites can mediate direct defences but also function as a vehicle of information transfer between organisms and so mediate complex interactions within the plant‐associated communities. Direct chemical defences can function as toxins, antidigestive or antinutrive agents and so reduce the nutritive value of the plant tissues for an attacking herbivore. Some secondary metabolites and physical structures can facilitate the presence and prey‐search behaviour of natural enemies of herbivores and so mediate indirect resistance. Plant defensive traits, in particular resistance‐mediating metabolites, tend to be functionally redundant, while individual compounds have multiple functions on different levels. Chemical and physical traits can be combined or function synergistically to reduce herbivore pressure. According to optimal defence theory, young tissues of high value to plant fitness tend to be chemically defended, whereas older tissues have relatively strong physical defences. Chemical defences, especially induced chemical defences, are tightly regulated by a complex interaction between endogenous and external elicitors and a subsequent signalling pathway crosstalk. Natural plant defences provide multiple sustainable options for pest control in agriculture.

Tomato Cultivars Resistant or Susceptible to Spider Mites Differ in Their Biosynthesis and Metabolic Profile of the Monoterpenoid Pathway

“…Moreover, they produce volatile organic compounds (VOCs) involved in direct and indirect defense responses (War et al, 2012). Ubiquitous and species-specific plant volatiles belong to a wide range of different biochemical classes, mainly phenylpropanoids and benzenoids, terpenoids, and aliphatics, which play a key role in direct or indirect defense (Cheynier et al, 2013;Kessler, 2017;Ameye et al, 2018).…”

Genomic and metabolic profiling of two tomato contrasting cultivars for tolerance to Tuta absoluta

“…Many genes with variants were identified in secondary metabolism and were involved in the biosynthesis of VOCs, including phenylpropanoids, flavonoids and terpenoids, which play a key role in direct or indirect defense (War et al 2012 ; Cheynier et al 2013 ; Kessler 2017 ; Ameye et al 2018 ; Erb and Kliebenstein 2020 ). In the cultivated tomato, acyl sugars, flavonoids, and terpenes are major secondary compounds produced in type I, IV and VI gland bearing trichomes in response to herbivore attack (Schilmiller et al 2009 ; McDowell et al 2011 ; Kang et al 2014 ; Bergau et al 2015 ; Balcke et al 2017 ).…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…This may include releasing a blend of specific floral volatile scents that attract predators of herbivores after being attacked (Kessler 2010;Peñuelas et al 2014)). In the model plant Arabidopsis, females of parasitoids Cotesia marginiventris use TPS10 (a sesquiterpene) to track their lepidopteran host by utilizing the floral scent (Schnee et al 2006).…”