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Winnowing out wheat genes of interest
Rome, Italy
For immediate release
One way to increase the chances of finding a needle in a haystack is to start with a smaller haystack. Michael Mackay, a scientist at Bioversity International, and a group of colleagues recently published a technique for doing just that for the very important needles that are genetic resources. The approach could make plant breeding in response to the challenges of climate change much more efficient and hence make an important contribution to future food security.
The researchers were looking for genes that might confer resistance to powdery mildew, a fungal disease of wheat that can reduce yields by up to 40%. Gene, in this context, takes on many meanings. Sometimes, when researchers talk about different resistance genes, what they really mean are different versions, or alleles, that occupy a particular place on the DNA, which in this case would be called a locus.
One such gene, or locus, is known as Pm3. Since it was first identified 100 years ago, researchers have identified 7 different alleles that can be present at the Pm3 locus, many of which confer resistance to different strains of powdery mildew. Because the Pm3 gene has been cloned, it is possible to use its DNA sequence to search for different alleles that might help to protect wheat against new strains of powdery mildew. The problem is that there are more than 560,000 samples of wheat held in almost 40 genebanks around the world. That’s a pretty big haystack; screening them all would be impractical.
Instead, Mackay and his colleagues used an approach they call FIGS, the Focused Identification of Germplasm Strategy. It works like this: take 400 genebank samples known to have some resistance to powdery mildew and use the geographical location where they evolved and were collected to determine the environmental profile that can be associated with resistance. Then apply that profile to a further 16,089 samples with location data, using the profile as a template to identify those that were found in places that share the conditions associated with resistance. The result is a group of 1320 wheat varieties, mostly from Turkey, Iran and Afghanistan. This much more manageable subset was screened by growing them with diverse strains of powdery mildew. About 16% of the samples (211 of 1320) showed some resistance.
These varieties then moved to the next phase, molecular screening for the presence of different alleles of the Pm3 gene. More than half (111 of the 211) had Pm3 resistance, some in previously unknown forms. In the end the group isolated and identified 7 new functional alleles of the Pm3 gene. It took scientists 100 years to find the first 7 Pm3 alleles. FIGS doubled the number in a fraction of the time.
Resistance to UG99 wheat stem rust
The result is important for several reasons, says Mackay. “It is going to help scientists and breeders to understand resistance to powdery mildew, and to come up with new and more resistant varieties. It also demonstrates that FIGS is an efficient and effective sampling strategy that’s going to a great help for breeders looking for any important adaptive traits in other crops.” Already in the pipeline is a study to help breeders find resistance to the deadly new strain of stem rust, UG99, that threatens global wheat crops.
Perhaps the most important message, however, is that all the new resistance genes were found in landraces, genetically diverse populations kept alive by farmers in harsh environments, who value the adaptability and resilience of these varieties. Improved varieties based on the genetic resources of landraces tend to displace the very landraces on which they depend, making conservation in genebanks essential.
“We need conservation in genebanks and in farmers’ fields,” says Emile Frison, Director General of Bioversity International, “and this result shows how farmers and breeders can make more effective use of genebank samples. We are going to need all the help we can get to adapt crops to the challenges of climate change, and FIGS is a useful tool for that work.”
ENDS
For further information, contact Jeremy Cherfas
Note to Editors:
Bhullar, N., Street, K., Mackay, M., Yahiaoui, N., & Keller, B. (2009). Unlocking wheat genetic resources for the molecular identification of previously undescribed functional alleles at the Pm3 resistance locus Proceedings of the National Academy of Sciences, 106 (23), 9519-9524 DOI: 10.1073/pnas.0904152106
This work depended on the co-operation and inputs of several partners: ICARDA, VIR, AWCC, GRDC and the University of Zurich.
Bioversity International, with its Headquarters in Rome, Italy, has worked for more than 35 years to support the improved use and conservation of agricultural diversity. Through international research, in collaboration with partners throughout the world, Bioversity strives to build the knowledge base needed to ensure effective use of diversity to increase sustainable agricultural production, improve livelihoods and meet the challenge of climate change.
