Phytohormone-based activity mapping of insect herbivore-produced elicitors

Abstract

In response to insect attack, many plants exhibit dynamic biochemical changes, resulting in the induced production of direct and indirect defenses. Elicitors present in herbivore oral secretions are believed to positively regulate many inducible plant defenses; however, little is known about the specificity of elicitor recognition in plants. To investigate the phylogenic distribution of elicitor activity, we tested representatives from three different elicitor classes on the time course of defense-related phytohormone production, including ethylene (E), jasmonic acid (JA), and salicylic acid, in a range of plant species spanning angiosperm diversity. All families examined responded to at least one elicitor class with significant increases in E and JA production within 1 to 2 h after treatment, yet elicitation activity among species was highly idiosyncratic. The fatty-acid amino acid conjugate volicitin exhibited the widest range of phytohormone and volatile inducing activity, which spanned maize (Zea mays), soybean (Glycine max), and eggplant (Solanum melongena). In contrast, the activity of inceptinrelated peptides, originally described in cowpea (Vigna unguiculata), was limited even within the Fabaceae. Similarly, caeliferin A16:0, a disulfooxy fatty acid from grasshoppers, was the only elicitor with demonstrable activity in Arabidopsis thaliana. Although precise mechanisms remain unknown, the unpredictable nature of elicitor activity between plant species supports the existence of specific receptor-ligand interactions mediating recognition. Despite the lack of an ideal plant model for studying the action of numerous elicitors, E and JA exist as highly conserved and readily quantifiable markers for future discoveries in this field.ethylene ͉ insect elicitor ͉ jasmonic acid ͉ plant defense ͉ volatile organic compound

Identity, regulation, and activity of inducible diterpenoid phytoalexins in maize

“…Plant defense responses to biotic attack are often mediated by the synergistic phytohormone actions of E and oxylipin signals, such as JA (18,26,27). To examine the potential role of induced oxylipins as regulators of kauralexin production, damaged stems were inoculated with R. microsporus.…”

“…Elicitors present in the oral secretions of insect herbivores commonly induce terpenoids in the leaves of plants (18). To explore related defensives in maize stems, we examined O. nubilalisinduced metabolites.…”

Discovery, Biosynthesis and Stress-Related Accumulation of Dolabradiene-Derived Defenses in Maize

“…Seeds of hybrid maize (Zea mays variety Golden Queen; Southern States Cooperative), landrace inbreds (B73, Mo17, and W22; National Genetic Resources Program, Germplasm Resources Information Network), and a Ds insertion mutant, Zman2 (Vaughan et al, 2015), were germinated in MetroMix 200 (Sun Gro Horticulture) supplemented with 14-14-14 Osmocote (Scotts Miracle-Gro) and grown as described previously (Schmelz et al, 2009). Fieldchallenged roots from B73, Mo17, Ky21, and hybrid sweet corn grown at the Biology Field Station at the University of California, San Diego, during the summer of 2016 were recovered 75 d after planting, washed, frozen in liquid N 2 , ground to a fine powder, and ultimately used for metabolite analysis.…”

Empoasca leafhoppers attack wild tobacco plants in a jasmonate-dependent manner and identify jasmonate mutants in natural populations

“…In their natural environment, as well as in the glasshouse, N. attenuata plants respond strongly and specifically to attacks by insects of different feeding guilds (23,24). A large number of these responses are governed by a strong burst of JA, which is amplified by elicitors in the insect's oral secretions (OS) (10,(25)(26)(27). The initial steps of JA biosynthesis involve the release of trienoic fatty acids [e.g., α-linolenic acid (18:3)] from membrane lipids in the chloroplast by the action of glycerolipases [GLA1 in N. attenuata (28,29)].…”