By Scott Weybright, College of Agricultural, Human & Natural Resource Sciences
The Washington State University research is the featured paper in the November issue of The Plant Journal.
The finding involves large-scale gene sequencing and characterization of the proteins that participate in metabolic pathways in plants.
New role for enzyme
“We identified a new function for a class of enzyme that was thought to only be involved in basic leaf functions, like photosynthesis,” said David Gang, associate professor and fellow in the WSU Institute of Biological Chemistry. “This opens up doors for investigations of other pathways in other plants.”
Post-doctoral fellow and lead author Anna Berim determined that a Rieske-type oxygenase protein was being used by the basil plant in its chemical defense. Previously, that protein type was only known to be involved in chlorophyll production.
Plants have two kinds of metabolism, or chemical processes involved in how they grow and interact with the environment. They have primary metabolism, like photosynthesis, and specialized metabolism, like that responsible for producing plant defense and medicinal compounds.
Mystery gene key for flavor
Berim was studying how basil plants produce flavones, a class of compounds that are part of specialized metabolism in some plants. She specifically looked at special cell types called glandular trichomes, where the characteristic flavor compounds are produced in basil, peppermint and other herbs.
She found that one step in the flavone production pathway was carried out by the Rieske-type oxygenase, a class of enzyme previously thought to be involved only in primary metabolism. Finding it in the flavone pathway in the flavor production area was a surprise.
“It’s an unusual gene for the glandular trichomes, and it was expressed at very high levels, suggesting that it was doing something important,” Gang said. “But those trichomes don’t do photosynthesis and have no chlorophyll, so we had no idea what it was doing.
“Recently, Anna had a hunch that maybe this mystery gene was involved in the flavone pathway,” he said. “And she was right.”
Unblocking other pathways
Before this research, there were only two major classes of enzymes known to perform an important kind of step in specialized metabolism. Berim was trying to figure out that step in the flavone pathway, but neither of these known enzyme classes worked. They didn’t make the flavones she was looking for.
When she tested the Rieske-type oxygenase, she found that it not only worked but was extremely efficient for that step in the flavone pathway. She had found the missing piece – and identified a new role for that type of enzyme.
The research should open doors for other scientists who reach a roadblock in their research, Gang said: They can try this class of enzyme or even consider other types of genes that don’t have a known type of function.
“We’re hoping that our finding will help accelerate the overall study of biosynthetic pathways,” Berim said.
The article can be found at: Berim, A., Park, J.-J. and Gang, D. R. (2014), Unexpected roles for ancient proteins: flavone 8-hydroxylase in sweet basil trichomes is a Rieske-type, PAO-family oxygenase. The Plant Journal, 80: 385–395. doi: 10.1111/tpj.12642