"It's just like taking a 10-word sentence from a book and asking where it belongs," he said. "It finds the location of a specific sequence inside the species genome. The mutation is like a misplaced period in the middle of a sentence – it signals the reader to stop. In the case of the sorghum mutant, it halts the production of a functional protein."
The sequencing technique allowed Tuinstra and Dilkes to identify the single nucleotide within the sorghum genome of 790 million base pairs that slowed the release of cyanide in the mutant plant.
"This study is an example of how new methods in DNA sequencing can now be used to unlock the genetic mechanisms of sorghum performance," Tuinstra said.
After cloning the mutant, the researchers tested insect feeding preference by releasing fall army worms onto mutant and normal sorghum plants. Though both types of sorghum contained normal levels of dhurrin, the insects avoided the normal sorghum plants, settling and feeding on the leaves of the mutant sorghum instead. While the mutant contains the compounds necessary to generate cyanide, it cannot release cyanide quickly enough to ward off pests, Tuinstra said.
Next-generation sequencing is more often used in plant species with genomes much smaller than sorghum. The study clears the way to use advanced sequencing techniques to identify genes and gene functions in plants with large genomes, Dilkes said.
"We've demonstrated that these sequencing tools are robust enough to apply to organisms with complex genomes," he said. "If we can use them in sorghum, we can use them in other crops. In terms of identifying genes of interest in complex organisms, we're open for business."