The Arabidopsis thaliana carboxylesterase AtCXE12 converts volatile (Z)-3-hexenyl acetate to (Z)-3-hexenol

Abstract

The green leaf volatiles (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate are produced by nearly all plants in response to wounding and insect attack, can be transferred between plants, metabolized, and act as defense cues. If and how plant leaves convert exogenous (Z)-3-hexenyl acetate to (Z)-3-hexenol is unknown. We show that Arabidopsis leaves rapidly convert exogenous (Z)-3-hexenyl acetate to (Z)-3-hexenol. Inhibitor and fractionation experiments identified the carboxylesterases AtCXE5 and AtCXE12 as likely contributors to (Z)-3-hexenyl acetate esterase activity in Arabidopsis leaves. Heterologous expression of AtCXE5 and AtCXE12 revealed that both enzymes hydrolyze (Z)-3-hexenyl acetate to (Z)-3-hexenol in vitro, and assays using T-DNA insertion mutant plants showed that AtCXE12 significantly contributes to the conversion of (Z)-3-hexenyl acetate to (Z)-3-hexenol in planta. Lastly, we found that leaves from several other plant species possess (Z)-3-hexenyl acetate esterase activity, as well as homologs of AtCXE5 and AtCXE12 from Arabidopsis. Collectively, our study provides a better understanding of green leaf volatile biosynthesis and conversion dynamics, necessary for unraveling the potential functions of these compounds.