CSIRO team clones wheat flowering gene

CSIRO Plant Industry researchers have cloned the gene that probably laid the foundation for Australia's lucrative wheat industry more than a century ago.

Dr Ben Trevaskis and his colleagues finished in a three-way tie with US and Canadian research teams to clone the gene, called WAP1, which plays a key role in initiating flowering in wheat.

In winter wheats grown in cold-climate regions of the northern hemisphere, WAP1 delays flowering until the plants have been exposed to a prolonged period of winter cold. The process, called vernalisation, suppresses flowering until the danger of damaging frosts has passed.

But Australian wheat production is almost exclusively from spring wheats that don't require vernalisation -- in Australia's warm climate, where the risk of frost damage during flowering is low, breeders have exploited 'always-on' variants of WAP1.

Trevaskis said WAP1 could be used to control flowering time in cereals, and his team is now conducting experiments to see if it can develop wheat plants that will flower when required.

In countries like Australia and India, where most wheat is grown under natural rainfall, earlier-flowering cultivars would reduce the risk of crops running out of water in dry years.

Trevaskis said he suspected WAP1 was crucial to the efforts of pioneering hybridist William Farrer, more than a century ago, to develop the first wheat varieties suited to Australian conditions.

Farrer, Australia's first successful cereal breeder, used wheat varieties from India to develop the first rust-resistant Australian spring wheats, including 'Federation', the celebrated cultivar on which Australia's lucrative wheat industry was founded.

But instead of selecting for rust-resistance genes, Farrer simply avoided the disease problem by breeding varieties that flowered later, avoiding the cool, moist conditions in which the rust fungus flourishes.

With most modern Australian wheat cultivars now well protected by multiple rust-resistance genes, earlier flowering could help insulate rain-grown wheat -- and other cereals -- against running out of water in dry years.

In the late 1990s, CSIRO researchers cloned the so-called master gene for flowering, 'flowering locus C' (FLC), from Arabidopsis. FLC actively suppresses flowering until multiple genes specialised for monitoring internal and environmental cues such as temperature and day length act collectively to switch it off.

The surprise from the WAP1 discovery, Trevaskis said, is that wheat and other cereals appear to have evolved a different system of flowering control. "We went looking for the functional equivalent of FLC in wheat, expecting to find an FLC-like gene, but it seems variation in this one gene, WAP1, has the major effect on flowering time and vernalisation response," he said.

Ancient system

Trevaskis said the ancestor of cereals once relied on a day length response to promote spring flowering, and this ancient system appears to be highly conserved in plants.

But glacial periods probably selected for a vernalisation response that overrode the day length response, delaying flowering until the risk of damaging frosts had passed. Other types from warmer regions retained WAP1 variants that remained constantly active -- they do not require vernalisation.

In the 1960s the great Australian wheat geneticist AT Pugsley performed a series of crosses that showed flowering time in wheat was controlled at a single genetic locus. The then-anonymous gene has now been identified as WAP1.

Trevaskis said that while semi-spring wheats can be cold-treated to induce the vernalisation response, neither the duration nor temperature of such exposure induces such cultivars to flower earlier.

He said it was likely that in the vast majority of wheats, differences in flowering time reflect variation in the DNA sequence of the WAP1 gene. He and his colleagues are now investigating the relationship between sequence variation and flowering time, with the aim of developing cultivars that will flower earlier, or at a chosen time in the season.

Trevaskis said WAP1 could also be used to completely block flowering in grasses like perennial ryegrass, that cause allergies like hay fever and asthma, or to prevent sugar cane flowering, diverting more resources into sucrose production.