How wheat lost the evolutionary battle against its deadly fungal nemesis

Researchers have identified a gene in wheat that protects against a deadly fungus, but which was lost from many wheat crops in the 1980s. The finding explains an epidemic of the fungus, which continues to this day, and suggests that restoring the gene in wheat could limit impacts of the fungal pathogen. Wheat blast first emerged in Brazil in the mid-1980s and has recently caused heavy crop losses in Asia. The pathogen that causes wheat blast, Pyricularia oryzae, is also known to affect other crops, such as rice, oats, and ryegrass. It attacks its host using two genes, PWT3 and PWT4. Recently, a group of researchers identified corresponding genes in oat and ryegrass that act as a counter-defense system against P. oryzae. Here, Yoshihiro Inoue and colleagues sought to explore whether these resistance genes, PWT3-Rwt3 and PWT4-Rwt4, would also protect wheat from the fungus, which they confirmed. Many strains of wheat still retain these protective genes; however, a strain introduced in Brazil just before the outbreak of wheat blast lacks them. Not knowing this, others outside of Brazil used this strain of wheat for their own agriculture. By analyzing a global database of wheat genomes, the authors were able to trace the loss of PWT3-Rwt3 across continents, finding that it corresponded with the spread of wheat blast. Around the same time, analyses show, the fungus acquired mutations in its offensive gene PWT3, which boosted its ability to infect hosts. These findings suggest that a combination of genetic changes likely contributed to the outbreak of wheat blast. Takaki Maekawa and Paul Schulze-Lefert discuss this study in a related Perspective.

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http://dx.doi.org/10.1126/science.aam9654

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