Summary: Green‐leaf volatiles are commonly emitted from mechanically and herbivore‐damaged plants. Derived from the lipoxygenase pathway, these compounds may serve as attractants to predators and parasitoids of herbivores, prevent the spread of bacteria and fungi, and induce several important plant defense pathways. In Arabidopsis thaliana, the major volatile released upon mechanical wounding of the leaves is the GLV ester, (Z)‐3‐hexen‐1‐yl acetate. We have characterized a member of the BAHD acyltransferase gene family At3g03480 which catalyzes the formation of (Z)‐3‐hexen‐1‐yl acetate from acetyl‐CoA and (Z)‐3‐hexen‐1‐ol. The encoded acetyl CoA:(Z)‐3‐hexen‐1‐ol acetyltransferase (CHAT) has the ability to accept several medium‐chain‐length aliphatic and benzyl‐derived alcohols, but has highest catalytic efficiency with (Z)‐3‐hexen‐1‐ol. The highest expression of CHAT occurs in the leaves and stems. Upon mechanical damage, the (Z)‐3‐hexen‐1‐yl acetate emission peaked after 5 min and declined to pre‐damage levels after 90 min. However, CHAT gene transcript levels increased much more slowly with the highest levels detected between 3 and 6 h after wounding. An increase in CHAT enzyme activity in vitro followed the transcript increase, with levels peaking between 10 and 12 h after wounding. Plants expressing either an RNAi cassette for the CHAT gene or plants harboring a T‐DNA insertion in the CHAT coding region had greatly reduced (Z)‐3‐hexen‐1‐yl acetate emission, showing that the CHAT enzyme is responsible for the in planta production of this ester.

Summary: Volatile esters impart distinct characteristics to the floral scent of many plants, and are important in attracting insect pollinators. They are also important flavor compounds in fruits. The ester benzylacetate is a major constituent of the floral scent of Clarkia breweri, an annual plant native to California. The enzyme acetyl‐CoA:benzylalcohol acetyltransferase (BEAT), which catalyzes the formation of benzylacetate, has been purified from C. breweri petals, and a cDNA encoding this enzyme has been isolated and characterized. The sequence of the 433‐residue BEAT protein does not show high similarity to any previously characterized protein, but a 35‐residue region from position 135–163 has significant similarity (42–56% identity) to several proteins known or suspected to use an acyl‐CoA substrate. E. coli cells expressing C. breweri BEAT produced enzymatically active protein, and also synthesized benzylacetate and secreted it into the medium. Of the different parts of the C. breweri flower, petals contained the majority of BEAT transcripts, and no BEAT mRNA was detected in leaves. The levels of BEAT mRNA in the petals increased as the bud matured, and peaked at anthesis, paralleling changes in BEAT activity. However, three days after anthesis, mRNA levels began a steep decline, whereas BEAT activity remained high for the next two days, suggesting that the BEAT protein is relatively stable.