Wild grass could provide new targets for wheat and barley breeding research

Plant scientists have made a breakthrough that could lead to new, high-yielding, disease-resistant crop varieties.

Almost all wheat grown today is a ‘semi-dwarf’ breed from a naturally occurring mutant line with an altered giberellic acid (GA) signalling pathway.

First developed during the ‘Green Revolution’ of the 1960s, these varieties allow farmers to significantly increase crop yields because they respond to additional nitrogen by increasing yield without growing too tall and falling over (lodging) which negates the yield improvement and leads to issues with fungal infections of the heads and mycotoxin contamination of grain. The ability to increase yield per unit area has helped poorer economies to improve food security.

An added benefit of GA-defective semi-dwarf plants is that they also show increased resistance to necrotrophic fungi that kill the plant and feed from the dead tissues. But there is a trade off because these plants are also more prone to diseases caused by biotrophic fungi that feed on living tissues.

Research into the genetic improvement of domesticated crops is difficult because they have large, complex genomes, and take up a lot of growing space. Using model species with small genomes and a compact size is useful in helping to understand crop plants, but the question remains: can what we have learned in a model be translated to a more complex species?

New research published in the journal Molecular Plant & Microbe Interactions suggests that yes, the wild grass Brachypodium distachyon is an ideal model for studying disease resistance traits in wheat and barley.

Rachel Goddard, lead co-author with Antoine Peraldi, is a PhD student in the lab of Paul Nicholson, said: “We have been investigating another plant signalling system – the brassinosteroid (BR) signalling pathway – in barley, a close relative of wheat. Like GA-defective plants, barley with a mutated BRI1 gene also seems to be a high yielding semi-dwarf that is more resistant to necrotrophic fungi. But in this case, the plants do not have an increased susceptibility to biotrophic fungal disease.”

Crucially, Rachel, Antoine and Paul have found that B. distachyon acts as a host to many of the same fungal pathogens that infect wheat and barley.

Most excitingly, they showed that when genes in the BR-signalling pathway of B. distachyon are disrupted, the same disease resistance traits are observed as in barley. This suggests that the mechanisms associated with this pathway are conserved between barley and its grass relative.

Rachel said: “The fact that the B. distachyon BR-signalling pathway responds in the same way as barley is exciting because it demonstrates the huge potential for this wild grass as a beautiful model species for wheat and barley breeding research. B. distachyon grows quickly, has a relatively simple genome, and unlike arable crops can be grown in a standard lab growth chamber. Hopefully, by working with this model, scientists can assist plant breeders to identify new targets genes to breed even higher yielding crops.

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