Researchers move closer to breaking herbicide resistance in black-grass

By Michael Keaveny

Scientists have adapted genetic techniques developed for crop improvement to be used in weeds - allowing them, for the first time, to directly study the genetics responsible for herbicide resistance.

The scientists from Rothamsted Research in Britain reported they have used plant viruses to switch weed genes off or, alternatively, ramp up the production of specific proteins by weeds in the laboratory. This means that these researchers can now directly show that a specific gene is required for herbicide resistance, or else is sufficient to confer it. Lead researcher Dr Dana MacGregor said the research was a 'game-changer' for weed genetics.

The study focused on black-grass, a major weed of cereals, and a previous joint study involving the same team showed that herbicide-resistant black-grass could cost £1bn every year in the UK alone.

Dr MacGregor said: "Weeds are arguably one of the most economically important groups of plant species. They have major agronomic and environmental impacts and affect food security.

"To be able to design and deploy weed management strategies that are both effective and sustainable, we must first understand what genes allow black-grass to avoid the current control practices.

"These virus-mediated techniques allow us to bring black-grass into the lab and ask questions about how specific genes work as we have never been able to before."

Two methods were developed for studying crop plants, with both taking advantage of the pathways plants and their viruses use to fight one another. These are called virus-induced gene silencing (Vigs) and virus-mediated over-expression (Vox). The team first inserted their gene of interest into a virus and then infected the weed with it.

During Vigs, the plant tries to defend itself and, in the process, shuts down production of all genes coming from the virus - including the weed's own copies of the inserted gene - whereas, during Vox, both the virus's and the inserted gene's copies manufacture proteins for the plant.

Having shown that the techniques worked using the appropriate controls, including inducing loss of green colour and making the plants fluoresce, they then turned their attention to genes implicated in herbicide resistance. This time, they used gene silencing to turn off a gene previously thought to confer herbicide resistance. This made previously resistance plants susceptible, thereby proving the involvement of the gene.

They also managed to make previously susceptible weeds resistant to the weed killer glufosinate by introducing a gene for an enzyme that renders the chemical inactive.

According to Dr MacGregor, although these techniques can be further improved, the Vigs and Vox techniques they have established offer a step-change in the type of questions that can now be asked in weed biology.