Plants that make rabbits sterile

Research being done at the Murdoch University-based State Agricultural Biotechnology Centre could help deal with Australia's increasing rabbit population.

Murdoch PhD student Peiling Tan is genetically engineering plants that could be used to reduce rabbit fertility.

The research is funded by the Cooperative Research Centre (CRC) for Legumes in Mediterranean Agriculture and the Vertebrate Biocontrol CRC.

Ms Tan is modifying plants to produce an animal protein that can be used as a vaccine to immunise rabbits. Controlling fertility using vaccines is a concept known as immunocontraception. Delivery of the protein into the rabbit creates an antibody response. This can result in reduced fertility if the antibodies can be tricked into attacking the rabbit's own eggs as though they were foreign cells.

"Our hope is to make them sterile, but that may not be possible," said Ms Tan. "A reduced fertility is the next best thing."

Traditional approaches to the rabbit problem, such as poisoning, have proven ineffective and rabbits have developed some resistance to the disease Myxomatosis. Sterilisation is a more humane way to control the rabbit population.

The process of modifying the plants is simple. Cut plant material is soaked in a solution of soil bacteria called Agrobacterium. The bacteria have been modified to contain the animal DNA. The bacteria infect the plant material, transfer the animal DNA into plant cells where it integrates into the plant DNA.

The plant tissue is regenerated in culture using hormones to grow shoots and then transferred to a tub containing hormones that promote root growth. Once roots grow the plant is transferred to soil.

Research has not proceeded to the stage of delivering the animal protein into the rabbit's system, but Ms Tan said this could be done by extracting the protein from the plant, then purifying and injecting it into the rabbit, or the plant could be crushed and fed to the rabbit.

While other research is being done into infecting rabbits by way of viruses, Ms Tan said using plants was potentially a cheaper and easier way of delivering the vaccine.

"The reason why I'm using plants is that this particular protein hasn't been produced in plants before," she said. "So we want to see whether it can be produced in plants. The other reason is if it can be produced in plants it will reduce the cost, because it's cheaper to grow plants than to use other systems such as viruses."

Ms Tan is genetically modifying two types of plants — tobacco and clover.

"Tobacco is a very easily modified plant," said Ms Tan. "But clover is the main aim, because rabbits will eat clover. It's part of their diet."

Ms Tan is using an animal protein from the zona pellucida. The zona pellucida is a membrane that surrounds the egg in a female animal.

She is using the zona pellucida protein from pigs, which is very similar to the protein in rabbits. The pig protein has been shown to induce antibodies in a range of animals.

Rabbit zona pellucida protein may be studied at a later date. However, the rabbit protein may not work because the rabbit's immune system might not produce antibodies in reaction to the presence of 'self' rabbit proteins.

Ms Tan said she expected to continue her research for another two years.

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