The carboxylesterase AtCXE12 converts volatile (Z)-3-hexenyl acetate to (Z)-3-hexenol in Arabidopsis leaves.

Abstract

The green leaf volatiles (GLVs) (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate play important roles in plant defense, deterring insect herbivores and attracting their natural enemies, while also serving as airborne signaling molecules capable of enhancing defenses in undamaged plant tissues. Almost all plants produce GLVs after wounding, beginning with the formation of (Z)-3-hexenal, which is subsequently converted to (Z)-3-hexenol and (Z)-3-hexenyl acetate. (Z)-3-hexenyl acetate can then be taken up by nearby plant tissues where it is predicted to be hydrolyzed to (Z)-3-hexenol, a process that is likely to be important in regulating the specific activities of these compounds. However, the enzyme(s) involved in this process and its role in plant defense are largely unknown. Here, we show that Arabidopsis (Arabidopsis thaliana) plants rapidly take up (Z)-3-hexenyl acetate and convert it to (Z)-3-hexenol. Inhibitor and fractionation experiments identified the carboxylesterases Carboxylesterase 5 (AtCXE5) and Carboxylesterase 12 (AtCXE12) as likely contributors to the (Z)-3-hexenyl acetate esterase activity in Arabidopsis leaves. Heterologous expression of AtCXE5 and AtCXE12 in Escherichia colirevealed that both recombinant enzymes hydrolyze (Z)-3-hexenyl acetate to (Z)-3-hexenol. Furthermore, assays using T-DNA insertion mutants showed that AtCXE12 significantly contributes to (Z)-3-hexenyl acetate hydrolysis in Arabidopsis. Lastly, we found that leaves from several other plant species possess (Z)-3-hexenyl acetate esterase activity, suggesting a conserved mechanism for GLV metabolism among plants. Overall, our study provides a better understanding of the biosynthesis and conversion dynamics of GLVs, which is necessary for unraveling the potential functions of these compounds.