Genetic ‘switch’ in wheat may halt pre-harvest sprouting

Developing new wheats to resist pre-harvest sprouting may take more than just breeding it out, new research from McGill University shows.

A McGill team led by plant science professor Jaswinder Singh has identified a gene in wheat that acts as a “switch” to determine how a plant will respond to high humidity and excess rainfall — either by germinating early, or not.

Pre-harvest sprouting (PHS) in Canada’s spring wheat crop alone is estimated to cost about $100 million a year in reduced grain yield, end-use quality and viability of seed for planting, the researchers said in their recently published study.

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Worldwide, the researchers said, PHS losses can cost wheat growers as much as $1 billion a year.

Scientists have tried over at least the past two decades to prevent PHS by focusing on genetic factors, and on the interaction between genotypes and the environment. Such research, the McGill team said, has involved trying to breed wheat resistant to PHS, “but with little success so far.”

PHS resistance or susceptibility is mainly influenced by seed dormancy, a complex trait. Reduced seed dormancy, however, is also influenced by “various environmental factors including light, temperature and abiotic stresses,” the team said.

The “switch” is found in what the McGill researchers call the ARGONAUTE4_9 gene, in the “RNA dependent DNA methylation” pathway (RdDM).

“The complex RdDM machinery is composed of several proteins that guide the genome in response to growth, developmental and stress signals. It’s a bit like the plant’s brain,” Singh said in the university’s release last week.

“Although in the past scientists have identified it as the pathway that regulates the way a variety of genes are expressed, until now no one had made the link with PHS.”

The team’s results suggest a role for the genetic switch in seed dormancy.

In that case, PHS resistance could then be developed not just by breeding for a particular gene, but by modulating a plant’s DNA methylation — that is, the signal mechanism a cell uses to switch off a gene’s expression.

“Ugly bread”

The McGill study compared 10 wheat varieties with “varying degrees” of seed dormancy in a growth chamber, including PHS-resistant or -tolerant varieties such as Snowbird, AC Domain, AC Karma, Thatcher and AC Vista, PHS-susceptible lines such as AC Andrew, and a “medium PHS reaction” variety, CDC Teal.

The researchers used genomic and molecular tools to identify specific ARGONAUTE4_9 genes, then compared how they’re expressed in PHS-resistant wheats against PHS-susceptible varieties.

Surinder Singh, a Ph.D. student and one of the study’s authors, said the finding will be helpful in other cereal crops as well, such as barley.

“This means that not only should we be able to avoid the ugly bread and sticky crumbs produced by PHS wheat in future, we should also end up with better beer.” — Network

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