Pigs turn up their snouts and chickens their beaks at feed containing toomuch rapeseed protein meal. Rapeseed (Brassica napus), or canola asCanadians call it, is a cash crop north of the border worth some C$2billion (U.S. $15 billion) a year. Animal feed is a hefty byproduct ofthe canola industry.
Plant biochemist Vincenzo De Luca, of the University of Montreal's PlantBiology Research Institute, is applying "metabolic engineering" to enhancethe canola meal's palatability and nutritional quality. His strategy toget rid of the plant's secondary metabolite, indole glucosinolate.
In Tuesday's issue of Proceedings of the National Academy of Sciences(PNAS), De Luca tells how he constructed a transgenic rape plant in whichthe unwelcome compound is down from 6 micromoles per gram of seed to0.2 mM. to 3 percent. His paper is titled "Redirection of tryptophanleads to production of low indole glucosinolate canola."
To sidetrack the glucosinolate metabolic pathway, De Luca turned to a genehe already knew well. It comes from the Madagascan periwinkle (Catharanthusroseus), a tropical shrub from which Eli Lilly and Co. extracts vinblastineand vincristine. These two secondary metabolites are important anti-cancerchemotherapeutics.
"Basically we knew that the precursors for the indole-glucosinolate incanola would have to be tryptophan," De Luca said. "So what you need is agene that would accept tryptophan as a substrate and divert it intotryptamine, not indole-glucosinolate."
When he first cloned the tryptophan decarboxylase gene, it was in an effortto increase vincristine production in C. roseus, a project in which De Lucais still engaged. But thinking, "To what other practical use can we putthis gene?" he experimented with diverting the tryptophan pathway in canola.It worked.
Of 85 putative transgenic plants allowed to flower and set seed, 11actually expressed tryptophan decarboxylase activity. Their seedsaccumulated only 3 percent of the indole-glucosinolate found in controlplants.
"The data that we obtained is of such significance that we now need to findout how the transgenic plants will perform in the field," he said.He's hoping to set up some controlled, small-scale field trials this summer"to establish whether the transgenic trait will be maintained under theenvironmental conditions where the rapeseed plant normally grows"-- inCanada's harsh western prairies.
Having filed for patents on the gene and its material, the University ofMontreal is now looking for what De Luca calls "industrial inputs" --companies interested in supporting such trials, and the eventualcommercialization of the metabolism-detouring approach.
"We are already in consultation with our regulatory organism,Agriculture-Canada," he said. "This national agricultural organization,among others, regulates all plants that are going to be approved."
Calgene Has Its Doubts
Calgene Inc., of Davis, Calif., has its doubts. The company's vicepresident of research, Vic Knauf, has talked with De Luca "about whetheror not there would be some regulatory aspect, the fact that he'srechanneling this into a different compound." Knauf told BioWorld thatAgriculture Canada is like the USDA, "but this is an FDA issue, not anAg-Canada issue."
Knauf makes the point that labs in Canada and elsewhere are "knockingdown that glucosinolate pathway lower and lower by mutagenizing therapeseed. From our viewpoint," he said, you don't have to do geneticengineering; it's not transgenic and gets to the same place."
Knauf concluded: "De Luca has an interesting principle. We've thoughtabout the prospect, and we have not yet seen a commercial route of anyinterest for Calgene. But that's not to say that someone else might."That someone else, De Luca hopes, might be Dupont or Monsanto orPioneer-Hybrid, all of which have major canola activities. "What we havein our hands," he said, "is something that would add value to the mealfrom which canola oil is pressed. When you have one trait, if you havetwo, it's better, especially if you can give it for the same price."Nutritionists tell him that decreasing the glucosinolate content willimprove the nutritional value of the animal feed. And improving itspalatability will mean a higher percentage of the meal can be added tothe feed without turning off the pigs and chickens.031694Canola Metabolite
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.