An Investigation of the Metabolic Fate and Possible Evolutionary Origin of Green Leaf Volatiles

open_access
Open Access
Author:
Cofer, Tristan
Graduate Program:
Entomology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 21, 2022
Committee Members:
Don Bryant, Outside Unit & Field Member
John Tooker, Major Field Member
Tanya Renner, Major Field Member
Gary Felton, Program Head/Chair
Gary Felton, Chair & Dissertation Advisor
Keywords:
Green leaf volatiles
carboxylesterase
glycosyltransferase
CYP74
Nostoc
Abstract:
Green leaf volatiles (GLVs) are C6 aldehydes, alcohols, and their esters that are produced by nearly all green plants in response to mechanical damage and associated stresses, such as insect herbivory. GLVs can serve as direct defenses with toxic or repellent effects on insect herbivores and as indirect defenses that attract the natural enemies of an attacking herbivore. GLVs can also function as within- and between-plant signaling molecules, able to prompt undamaged plant tissues to prepare their defenses in advance of herbivore attack. The biological activity of specific GLVs is influenced largely by their distinct physical and chemical properties. Accordingly, the active metabolism of GLVs by plants is predicted to be important for the appropriate management of plant defenses. This dissertation investigates the metabolic fate and possible evolutionary origin of GLVs. In Chapter 2, I show that Arabidopsis plants absorb the GLV (Z)-3-hexenyl acetate, after which it is sequentially hydrolyzed to (Z)-3-hexenol and glycosylated. Furthermore, I identify two carboxylesterases from Arabidopsis leaves that hydrolyze (Z)-3-hexenyl acetate in vitro, and I demonstrate that the carboxylesterase CXE12 significantly contributes to the hydrolysis of exogenously applied (Z)-3-hexenyl acetate in planta. In Chapter 3, I extend these findings by demonstrating that the glycosyltransferase UGT85A2 significantly contributes to the glycosylation of (Z)-3-hexenol in Arabidopsis leaves. Lastly, in Chapter 4, I characterize a cytochrome P450 enzyme from the cyanobacterium Nostoc punctiforme PCC 73102, and establish a hitherto unrecognized phylogenetic relationship between this enzyme and those responsible for initiating the production of GLVs in plants. Collectively, these results provide evidence that the metabolism of GLVs may play a crucial role in regulating plant defenses, and advance a novel hypothesis to explain the evolutionary origin of GLVs and other related plant metabolites.