Genome editing’s role in crop improvement is in its infancy. Though CRISPR’d mustard greens and a tomato have made headlines, using CRISPR to help feed the world has not been broadly utilized.
Rice, which is amenable to genome editing, is a staple food for half of the world. However, rice blast, caused by the fungal pathogen Magnaporthe oryzae, results in large-scale annual losses. Now, CRISPR has been used to successfully engineer broad-spectrum disease resistance in rice plants (Oryza sativa). In addition, small-scale field trials in China showed that the newly created rice variety exhibited both high yields and resistance to the fungus.
This research is published in Nature in the paper, “Genome editing of a rice CDP-DAG synthase confers multipathogen resistance.”
The roots of the discovery began when Guotian Li, PhD, was a postdoc in the lab of Pamela Ronald, PhD, professor in the department of plant pathology at the University of California, Davis. There, Li identified a strain that would prove promising out of the 3,200 rice strains they sequenced.
“He found that the strain was also resistant to bacterial infection, but it was extremely small and low yielding,” Ronald said. “These types of ‘lesion mimic’ mutants have been found before but only in a few cases have they been useful to farmers because of the low yield.”
More recently, in his lab at the Huazhong Agricultural University in Wuhan, China, Li used CRISPR-Cas9 to isolate the gene related to the mutation in the strain and recreate that resistance trait—identifying a line with good yield and resistance to three different pathogens, including the fungus that causes rice blast.
Li’s team isolated a lesion mimic mutant (LMM) and demonstrated that a 29-base-pair deletion in the gene RESISTANCE TO BLAST1 (RBL1)—which encodes a cytidine diphosphate diacylglycerol synthase required for phospholipid biosynthesis—caused broad-spectrum disease resistance and caused an approximately 20-fold reduction in yield. Mutation of RBL1, they noted, results in reduced levels of phosphatidylinositol and its derivative phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), which is thought to have a role as a disease-susceptibility factor.
In small-scale field trials planted in disease-heavy plots, the new rice plants produced five times more yield than the control rice, which was damaged by the fungus, Ronald said.
“Blast is the most serious disease of plants in the world,” she added, “because it affects virtually all growing regions of rice and also because rice is a huge crop.”
The researchers hope to recreate this mutation in commonly grown rice varieties. Currently, they have only optimized this gene in a model variety called “Kitaake” which is not grown widely. They also hope to target the same gene in wheat to create disease-resistant wheat.
“A lot of these lesion mimic mutants have been discovered and sort of put aside because they have low yield,” Ronald said. “We’re hoping that people can go look at some of these and see if they can edit them to get a nice balance between resistance and high yield.”