Molecular technology reveals how the induced direct defenses of plants work

Plants do not endure herbivore attack passively but respond with a coordinated array of defensive strategies. Many toxic compounds and proteins elicited by herbivore attack are thought to increase the plant's resistance to future attack and thereby function as direct defenses. However, whether these compounds are actually responsible for induced direct defense remains unclear because the available evidence is largely correlative. Recent advances in understanding the genetic basis of resistance traits and their signaling pathways allow researchers to directly manipulate induced direct defenses and we review this growing literature. Also, these studies repeatedly demonstrate that changes in single traits rarely account for the phenomenon of induced defense. Transcriptional analysis performed during induction reveals the complexity of the metabolic reconfiguration in which direct defense traits are embedded. We conclude that genetic alterations of regulatory elements coordinating these complex changes will likely provide the most revealing manipulations and consider the controls necessary for a functional analysis of putative defense traits with transformed plants.