Figure 1.

An overview of the OS-elicited signaling cascade that activates direct defenses in Na’s leaves depicting the elements that were studied in the synthesized tetraploid and allopolyploid Nicotiana species. During herbivore attack by M. sexta larvae, FACs from larval OS bind to hypothetical receptors in the cell membrane at the attack site and activate unknown short-distance mobile signals. These signals activate mitogen-activated protein kinases that include SA-induced protein kinases and WIPKs that phosphorylate transcription factors (such as WRKYs), which in turn activate phytohormone signaling such as JA, SA, and JA-Ile and their associated biosynthetic genes such as LOX3, isochorismate synthase (ICS), and JAR4. By inhibiting ICS, NPR1 negatively regulates SA production and thereby SA/JA antagonism, allowing the expression of JA-mediated direct defenses such as nicotine, phenolics, TPIs, and diterpene glycosides (DTGs) that diminish the performance of M. sexta larvae feeding on elicited plants.