MANAGEMENT: Peter Alexander
DUKE INVENTOR: Xinnian Dong
Upstream Biotechnology uses patented technology to develop broad-spectrum disease-resistant crops to eliminate pesticide use, reduce production costs, and increase crop yield.
This novel method alters upstream DNA sequences to turn on a defensive gene while also using newly discovered sequence elements called upstream open reading frames (uORFs). The technology might also be used to produce various therapeutic proteins in plants.
Rice is one of the most important staple crops, responsible for providing over 1/5 of the calories consumed by humans worldwide. Diseases caused by bacterial or fungal pathogens present a significant problem and can result in the loss of 80% or more of a rice crop.
Although there is a long history of research into engineering disease-resistant plants, a practical application for using these methods in crops results in lower crop yield as the plant is diverting its energy to maintaining a constant active defense.
“Immunity is a double-edged sword, ” said study co-author Xinnian Dong, professor of biology at Duke and lead investigator of the study. “There is often a tradeoff between growth and defense because defense proteins are not only toxic to pathogens but also harmful to self when overexpressed,” Dong elaborated. “This is a major challenge in engineering disease resistance for agricultural use because the ultimate goal is to protect the yield.”
Previous studies have focused on altering the coding sequence or upstream DNA sequence elements of a gene. These upstream DNA elements are known as promoters, and they act as switches that turn on or off a gene’s expression. This is the first step of a gene’s synthesis into its protein product, known as transcription.
By attaching a promoter that gives an “on” signal to a defense gene, a plant can be engineered to be highly resistant to pathogens, though at a cost to growth and yield. These costs can be partially alleviated by attaching the defense gene to a “pathogen-specific” promoter that turns on in the presence of pathogen attack.
To further alleviate the negative effects of active defense, the Dong group sought to add an additional layer of control. They turned newly discovered sequence elements, called upstream open reading frames (uORFs), to help address this problem. These sequence elements act on the intermediate of a gene, or messenger (RNA, a molecule similar to DNA) to govern its “translation” into the final protein product. A recent study by the Dong lab in an accompanying paper in Nature has identified many of these elements that respond in a pathogen-inducible manner.
The Dong group hypothesized that adding this pathogen-inducible translational regulation would result in a tighter control of defense protein expression and minimize the lost yield associated with enhanced disease resistance.
The Dong group then sought to apply these findings to engineer disease-resistant rice, as it is one of the world’s most important crops. They created transgenic rice lines containing the transcriptional/translational cassette driving expression of another potent “immune activator” gene called AtNPR1. This gene was chosen as it has been found to confer broad spectrum pathogen resistance in a wide variety of crop species, including rice, citrus, apple and wheat.
The transgenic rice lines containing the transcriptional/translational cassette were infected with bacterial/fungal pathogens that cause three major rice diseases — rice blight, leaf streak, and fungal blast. These showed high resistance to all three pathogens, indicating broad spectrum resistance could be achieved. Importantly, when grown in the field, their yield — both in terms of grain quantity and quality per plant — was almost unaffected. These results indicate a great potential for agricultural applications.
This strategy is the first known use of adding translational control for the engineering of disease-resistant crops with minimal yield costs. It has many advantages, as it is broadly applicable to a variety of crop species against many pathogens. Since this strategy involves activating the plants’ endogenous defenses, it may also reduce the use of pesticides on crops and hence protect the environment.