Integrated view of plant metabolic defense with particular focus on chewing herbivores

Success of plants largely depends on their ability to defend against herbivores. Since emergence of the first voracious consumers, plants maintained adapting their structures and chemistry to escape from extinction. The constant pressure was further accelerated by adaptation of herbivores to plant defenses, which all together sparked the rise of a chemical empire comprised of thousands of specialized metabolites currently found in plants. Metabolic diversity in the plant kingdom is truly amazing, and although many plant metabolites have already been identified, a large number of potentially useful chemicals remain unexplored in plant bio-resources. Similarly, biosynthetic routes for plant metabolites involve many enzymes, some of which still wait for identification and biochemical characterization. Moreover, regulatory mechanisms that control gene expression and enzyme activities in specialized metabolism of plants are scarcely known. Finally, understanding of how plant defense chemicals exert their toxicity and/or repellency against herbivores remains limited to typical examples, such as proteinase inhibitors, cyanogenic compounds and nicotine. In this review, we attempt summarizing the current status quo in metabolic defense of plants that is predominantly based on the survey of ubiquitous examples of plant interactions with chewing herbivores.

Automated summary

The success of plants relies on their ability to defend against herbivores. Over time, plants have adapted their structures and chemistry to escape extinction and keep up with herbivores' adaptations to plant defenses. This has led to a wide variety of specialized metabolites found in plants. However, there is still much to explore in terms of potential chemicals and the enzymatic pathways involved in plant metabolites. Additionally, the regulatory mechanisms controlling gene expression and enzyme activities in plant specialized metabolism are not well understood. Understanding how plant defense chemicals work against herbivores is still limited to a few examples.