טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBenyamini Yael
SubjectAlcohol Acetyl Transferases and Sesquiterpene Synthases as
Biotechnological Tools to Improve Melon's Aroma
DepartmentDepartment of Biotechnology
Supervisors Professor Emeritus Shimon Gepstein
Dr. Nurit Katzir
Dr. Efraim Lwinshon


Abstract

Melon (Cucumis melon L.) is a highly polymorphic species that comprises a broad array of wild and cultivated strains. Melons strains differ in their aroma. The unique aroma of aromatic melons is due to volatile esters, mainly acetate derivatives that are prominent, together with lower levels of sesquiterpenes, as well as short-chain alcohols and aldehydes. Non-aromatic varieties often contain significantly lower levels of total volatiles, and they lack the volatile esters.

In this study, we examined the formation of two classes of volatile compounds: esters and terpenes. The last step in the biosynthesis of esters is catalyzed by alcohol acetyl transferase enzymes (AAT). AAT activity was examined in both aromatic and non-aromatic melons, and was detected only in the aromatic strains. Screening of a cDNA library revealed three cDNA clones that exhibited high similarity to the AAT gene family and their expression is up-regulated as the melon ripens. Two volatile sesquiterpenes, g-cadinene and d-cadinene, were found in the peels of ripe melons but not in the flesh. In accordance sesquiterpene synthase activity was also found only in the peel but not in the flesh of ripe fruit. Screening of cDNA libraries revealed two sequences with high similarity to gene members of the sesquiterpene synthase family. The enzymatic activity of one gene product was examined by heterologous bacterial expression. This gene encodes a sesquiterpene synthase enzyme that catalyses the formation of the sesquiterpene E, E α-farnesene from farnesyl pyrophosphate .