Researchers from the University of Texas report that manipulation of the hydroperoxide lyase (HPL) enzyme can change the production of green leaf volatiles (GLV) that give characteristic aromas to fruits and vegetables.
“Genetic engineering/modification (GM) of green leaf volatile production has important implications for manipulating food flavour," said Professor C.S. Raman, the senior author of the study.
"For example, the aroma of virgin olive oil stems from the volatiles synthesized by olives. By modifying the activity of enzymes that generate these substances, it may be possible to alter the flavour of the resulting oils."
The research, published online ahead of print in the prestigious journal Nature, focussed on changing one enzyme called allene oxide synthase (AOS) into HPL.
"Our work shows how you can convert one enzyme to another and, more importantly, provides the needed information for modifying the GLV production in plants,” said Raman.
Raman and co-workers focussed their attention of the popular plant model, Arabidopsis thaliana, and used 3-D images of the enzymes to make a small, but specific, genetic change in AOS, leading to the generation of HPL.
In plants, AOS produces jasmonate, which is responsible for the unique scent of jasmine flowers), while HPL produces GLV, which are responsible for the characteristic aromas to fruits and vegetables.
Both enzymes are members of larger cytochrome P450 enzyme family, found in most bacteria and all known plants and animals. In plants, AOS and HPL break down naturally-occurring, organic peroxides into GLV and jasmonate molecules. "Each flavour has a different chemical profile," Raman said.
Added pest control
The breakthrough could also have important implications for pest control and crop health, said the researchers, since green leaf volatiles and jasmonates also ward off predators. In fact, the volatile substances released into the air attract predators of their predators, explained Raman.
By tweaking the volatile release from plants, the scientists could produce plants with built-in, environmentally-friendly protection.
Commenting on the research, Rodney Kellems, professor and chairman of the Department of Biochemistry & Molecular Biology at the UT Medical School at Houston, said: "A notable strength of this manuscript is the combined use of structural and evolutionary biology to draw new insights regarding enzyme function.
“These insights led to the striking demonstration that a single amino acid substitution converts one enzyme into another, thereby showing how a single point mutation can contribute to the evolution of different biosynthetic pathways.
“This begins to answer the long-standing question as to how the same starting molecule can be converted into different products by enzymes that look strikingly similar," said Kellems, who was not involved in the research.
Published online ahead of print 20 August 2008, doi: 10.1038/nature07307
“Structural insights into the evolutionary paths of oxylipin biosynthetic enzymes”
Authors: D.-S. Lee, P. Nioche, M. Hamberg, C. S. Raman