Making Melons Taste Sweeter

Spanning two-decades, a BARD Fund-supported study has led to the complete characterization of the metabolic pathway responsible for the melon's sweet taste. The scientists have shown that almost twenty enzymatic reactions are involved in this process, and have further identified the key enzymes that determine the level of sucrose in the fruit.

One of the many joys of summer is to bask in the sun and feast on a freshly cut melon. But maybe this delectable experience could be even sweeter. It is the accumulation of sucrose during the final stages of fruit development that, to a large extent, endows melons with their sweet taste. A group of BARD Fund-supported scientists have been using physiology, biochemistry, genetics, and molecular biology tools to reveal how the melon plant regulates the accumulation of sugar in its fruit, with the goal of translating their findings into improved melon fruit produce.
In the earliest stages of the research, the scientists determined that the melon fruit's sweetness is due to a distinct metabolic transition during its development that leads to extensive accumulation of sucrose in its fruit. They further elucidated the complex pathway of sugar metabolism in the melon.
The scientists' research led to the identification and characterization of novel enzymes in the melon's sugar metabolism pathway. One such enzyme is "neutral alpha-galactosidase," which has unique biotechnological applications. The scientists' identification of this enzyme has led to the register of international patents for this discovery, and to the founding of a biotech company, Agazyme (www.agazyme.co.il), whose goal is to develop biotech uses for this enzyme.
Another newly discovered enzyme, a broad substrate UDPglucose/UDPgalactose pyrophosphorylase, was found to be crucial for the metabolism of the sugar galactose in the melon fruit. This enzyme, too, has unique properties with potential biotech applications.
Now that they have identified the key players in the melon's sugar metabolism during fruit development, the researchers are now working to characterize the genetic expression of these genes. They have, thus far, identified nearly fifty genes that encode for the numerous enzymatic reactions responsible for sugar metabolism, and have followed the genes' expression during fruit development. Notably, the scientists have observed that many of the sugar metabolism genes undergo a shift in their level of expression, which corresponds to the plant's switch from sugar utilization for growth to sugar storage.
The research group has also characterized the broad genetic variability for sugar content observed in the melon species and has identified the genetic information (i.e., quantitative trait loci) that determines the level of sucrose in the fruit. This knowledge can be used by breeders to improve the quality of the melon fruit.

The Core Group of Scientists:

• Prof. Mason D. Pharr, North Carolina State University, NC (recently deceased)
• Prof. Steven Huber, North Carolina State University, NC
• Dr. John Williamson, North Carolina State University, NC
• Dr. Arthur A. Schaffer, ARO - Volcani Center, Israel
• Dr. Beny Aloni, ARO - Volcani Center, Israel
• Dr. Nurit Katzir, ARO - Volcani Center, Israel
• Dr. Joseph Burger, ARO - Volcani Center, Israel
• Dr. Efraim Lewinsohn, ARO - Volcani Center, Israel
• Prof. Jim Giovannoni, Boyce Thompson Institute, NY
• Dr. Zhangjun Fei, Boyce Thompson Institute, NY