A key gene that trades off a plant's size with its resistance to disease has been found.
Plant geneticist Dr Sureshkumar Balasubramanian, from the University of Queensland, and colleagues, report their findings in today's issue of the journal Nature.
Scientists know that plants that develop resistance to disease pay a high price for this trait, says Balasubramanian.
But now Balasubramanian and colleagues have discovered the gene responsible.
The discovery was made accidentally while studying mouse-ear cress (Arabidopsis thaliana) for genes that govern how fast the plant grows.
They found that the slow-growing plants had a very active form of the gene called ACD6.
"The plants that carry the hyperactive allele of this ACD6 gene pay a very heavy price," says Balasubramanian.
But when the researchers checked to see how these plants fared in the presence of a wide range of plant pathogens, including a fungus, bacteria and aphids, they saw another side to the story.
"In the presence of pathogens, these plants outperformed the other ones," says Balasubramanian.
Balasubramanian says this kind of trade-off also occurs in humans. For example, people with sickle-cell anaemia have a mutation in their haemoglobin gene that also confers resistance to malaria.
"In the presence of a particular pathogen you are willing to tolerate the cost," says Balasubramanian.
He says the hyperactive form is present in around 20% of the general Arabidopsis thaliana population.
This percentage will increase in the presence of disease and ensure the community will survive regardless of whether there is disease around.
Balasubramanian says the findings underpin the importance of genetic diversity in agriculture.
He adds scientists may be able to use such natural alleles in "green genetic engineering".
Balasubramanian says because they occur in nature, it means they are less likely to interfere with other traits.
"In a sense they have been naturally tested," he says.