Team:RDFZ-CHINA/Description
I. The current state of the problem
Xanthomonas is one of the largest groups of the plant pathogen, each year billion of money is lost because of them. In this year's project, we focus on an alternative solution that can apply to all Xanthomonas and specifically to Xanthomonas orzyae which can cause serious rice disease.
Rice is a common crop resource for more than 50% of the global population. The massive growth of rice made it vulnerable to a large number of pathogens, including Bacterial Blight, caused by the bacterial pathogen Xanthomonas (Xoo), which leads to serious yield losses worldwide and threatens global food security. Due to the research, Xoo is capable of disseminating in the irrigation system, splashing, or wind-blown rain. The infection starts at the rice leaf margins and wounds in the leaves or roots and enter the xylem vessels after. Within days, the plants will start dying and form beads of exudate on the leaf surface.
II. Status of related technology development
The most commonly used method is the use of Chemical (benzoic acid, copper oxychloride) and antibiotic applications. Those chemical compounds could kill pathogens directly, as well as kill plant cells. Besides, bactericides have a research cycle of up to 10 years, which is far from keeping up with the speed of bacterial evolution. Furthermore, the large-scale application of pesticides has caused environmental pollution and accelerated the rate of bacterial reproduction and evolution, so the birth of super-bacteria is also a great threat to humans' future lives. Therefore, people must find out a better way to solve this serious problem.
Improving the control of farm practices sanitation is another choice, including publishing a proper watering regime, limiting crop density, and removing weed hosts. However, because most rice plants grow in the aquatic environment and Xoo could be disseminated through water media, this method could only bring limited effect. Rigid water monitoring systems are also still immature, which require significant sources while resulting in limited benefits.
Resistant cultivars, a more effective choice, made it possible to grow plants that can resist Xoo. However, most people still reject genetically modified food, making it a controversial issue. Since rice is a major food and starch resource for people in many countries, people require sustainable systems to endure the change. But many scientists still worry that large-scale applying genetic modified food decreases biodiversity and tolerance. What's more, Xoo has the capacity to express effectors that suppress some host defence responses, often this resistance is eventually overcome (Verdier et al., 2011).
Phage therapy is another kind of therapy using natural predatory relation between bacteria and phage. According to the mechanism of how phages kill the bacteria, it has less chance to generate super-bacteria, and terminate the whole species at a very fast speed. However, phage therapy has faced some unavoidable questions. (more detail in our design page https://2021.igem.org/Team:RDFZ-CHINA/Design)
III. Our solution
The Killer X we designed is basically an avirulent Xanthomonas carrying the phage DNA sequence. The phage sequence carried by the Killer X will be released as long as the bacteria receive the quorum-sensing signal DSF. This project can be separated into four different groups and worked with each other to achieve the goal. Due to our design, this system can rapidly respond to the presence of Xanthomonas without bringing too many negative effects to plants and the environment.
We plan to use pBBR plasmid and PXO99A Xanthomonas orzyae strain in our experiments because we can learn more information about this strain and plasmid.
Four systems we design:
1: Phage expression system: express the phage DNA sequence in the Xanthomonas orzyae
2: Repression system of phage key protein expression: repress the phage expression in the bacteria and only release it when DSF sensor system is activated
3: DSF sensor system: Quorum sensing system in the Xanthomonas will activate by DSF molecule. The influence in c-di-GMP will lead to the change on Vc2riboswtich, and further activate the downstream expression.
4: Gdpx1 overexpression system: avirulence system in the Xanthomonas, repress TS33 excretion system in the Xanthomonas which can decrease the plant's immune response.
2: Repression system of phage key protein expression: repress the phage expression in the bacteria and only release it when DSF sensor system is activated
3: DSF sensor system: Quorum sensing system in the Xanthomonas will activate by DSF molecule. The influence in c-di-GMP will lead to the change on Vc2riboswtich, and further activate the downstream expression.
4: Gdpx1 overexpression system: avirulence system in the Xanthomonas, repress TS33 excretion system in the Xanthomonas which can decrease the plant's immune response.
