Team:SZU-China/Description
Description
SZU-China 2019 team saw mountains of M. micrantha on our campus. This invasive weed brought a great disaster to our environment (click to see their conceptions on M. micrantha):
Fruit Farmer
Property Manager
Student
Professor Beixin Mo
Alien plants invade many ecosystems worldwide and have substantial negative effects on community structure and function. Such invasive plants, commonly called weeds, have been causing widespread environmental degradation for over 100 years. Invasive vines such as Mikania micrantha that smother existing plant communities attract significant attention because of threats they pose to biodiversity. Mikania micrantha, a perennial vine native to tropical Central and South America, is a pest in plantation crops and commercial forests, from Mauritius to West Africa and across Asia. It is one of the top 10 worst weeds in the world[1]. Because of its vigorous, fast, and rampant growth habit, M. micrantha has been called 'mile-a-minute' weed. It was introduced into China in the early 20th century, leading to the great destruction of the local environment. Moreover, with the increasing global warming, the living zone of M. micrantha is expanding, which is unpredictable and uncontrollable, leading to a great disaster to the ecosystem (Fig.1).
Fig.1 M. micrantha are twining around other litchi trees of our campus
Alarmed by the rapid growth and damage of M. micrantha, the Chinese government began investing resources to prevent further dispersal of the weed and to eliminate or remove it from infected areas. As one of the fastest growing metropolitan areas in China, Shenzhen, where we SZU-China team live, is the worst affected city infested with patchily distributed M. micrantha, where, of the 2700 ha infested forest in the area, 300 ha were almost dead[2]. Similarly on Neilingding island (an island of Shenzhen), 40–60% of this 478 ha national nature reserve were infested and some forests had already degraded to wasteland and 200 of the 600 plant species are suffering from overgrowth by M. micrantha[3]. Without effective control, this native habitat for over 600 rhesus macaques (Macaca mulatta Zimmermann), a protected species in China will be lost[4].
After interviewing Professor Beixin Mo, we sincerely invited her to be our primary instructor (PI).
Professor Beixin Mo
RNA interference (RNAi) technology was all the rage at a time, and the biologists almost scrambled to study the mechanism and the application of it. Then, as the technique of CRISPR gene editing got increasingly popular, the RNAi was not as hot as it used to be. However, RNAi-based herbicide is quite safer than any other chemical or biological technology. There are three major reasons as follows. First, the RNA interference molecules inside the plant, unlike the transgenic technique, cannot cause permanent changes in the gene expression, which means it would be accepted by the public more easily. Second, RNA molecules are not so stable as other chemicals and are easily degradable, so they are eco-friendly (for more information, see the Stability). Third, this kind of herbicide can only target and silence the essential gene of M. micrantha and do no harm to other plants.
Now, many farmers and conservationists always turn pale at M. micrantha. Every year, such destructive weed swallows thousands of fruit trees and many other plants, leading to countless economic losses and posing a great threat to ecology. While visiting Neilingding Island, we saw mountains of M. micrantha drowning other brushes and trees. It is said that the monkeys there died of hungry since this invasive vine destroyed their food resources, leaving no food for them to survive. This cold-blooded killer has vigorous vitality and can twine whatever it touches to grow upwards. It covers on the top of other trees, blocking the sunlight and leaving dead silence reigned everywhere under its body (Fig.2).
Fig.2 Picture of destructive M. micrantha
At present, there are three ways to remove M. micrantha[1].
| Current solution | Ex | Pros | Cons |
|---|---|---|---|
| Mechanical and manual control | In the growing season of M. micrantha in 2000, the Shenzhen government sponsored thousands of citizens to hand pull the weed | Removing M. micrantha manually is most effective as herbicides | Can have undesirable effects on non-target species and the environment, like pulling out the wrong plants or trampling the other species down |
| Chemical control | Effective herbicides include glyphosate, 2,4-D, napropamide and atrazine. Although spray applications of 2,4-D and glyphosate killed above-ground M. micrantha within 14 days and 4 weeks respectively, M. micrantha fully recovered after 3 months. | Can be useful in places where M. micrantha cover is dense or where manual removal is difficult | 1. Can have undesirable effects on non-target species and the environment, like toxic chemical residues 2. Although some progress had been made for chemical control of M. micrantha, many of the trial results still need to be tested on a large scale |
| Natural enemies and biological control | Although over 30 species of insects and mites were collected on M. micrantha and M. cordata, only a few insects, acarus and fungi were reported to be able to control the reproduction of M. micrantha. | Be considered as the most promising sustainable control strategy for this weed | May bring some unpredictable risks to the local environment |
SZU-China 2019 iGEM team decides to remove M. micrantha by silencing the essential metabolic gene of it through RNA interference (RNAi) technology. We analyzed the transcript of M. micrantha and selected the specific siRNA via the sifting program we designed, which can combine the target mRNA, leading to the degradation of it. (Click here to learn more about the sifting program) Then, we designed a sequence containing several regions that can form hairpin siRNAs, which can be cut into different kinds of siRNAs we need by Dicer enzyme inside the plant[5] (Fig.3).
Fig.3 Formation of Hairpin siRNA
Plasmid pET-28a(+) containing this sequence was constructed and transformed into E. coli ht115(DE3). The RNAi molecules transcribed in E. coli were extracted and sprayed on Mikania micrantha as an RNAi-based herbicide (Fig.4).
Fig.4 Mechanism of RNAi-based Herbicide
We built two self-cracking mechanisms, the refractile body (R-body) controlled by the change of pH and the lysis protein manipulated by the concentration of tryptophan, for our system, which can poke or decompose the plasma membrane of E. coli, causing the inclusion to flow out, so that we can get the RNAi molecules transcribed by E. coli (Click here to see more) Meanwhile, the E. coli is dead and can never pose any threat on other creatures(Fig.5).
Fig.5 Refractile body controlled by pH
Micrancide is quite safer than any other chemical or biological technology.
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RNA molecules are not so stable as other chemicals and are easily degradable, so they are eco-friendly (for more information, see the Stability).
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Micrancide can only target and silence the essential gene of M. micrantha and do no harm to other plants.
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Micrancide, unlike transgenic technique, cannot cause permanent changes in the gene expression of plants.
[1] Zhang, L Y , et al. "Mikania micrantha H. B. K. in China – an overview." Weed Research 44.1(2004).
[2] Hui-Ling, Feng , and CAO. "The Distribution and Harmful Effect of Mikania micrantha in Guangdong." Journal of Tropical and Subtropical Botany (2002).
[3] Liping, He , L. Qiying , and Y. Ruihua . "AN EXOTIC WEED: MIKANIA MICRANTHA——ITS DISTRLBUTION AND HARMFULLNESS IN SHENZHEN." Forestry Science and Technology (2000).
[4] Feng, Huiling, et al. "The distribution and harmful effect of Mikania micrantha in Guangdong." Journal of Tropical & Subtropical Botany 10.3(2002):263-270.
[5] Lee J B , Hong J , Bonner D K , et al. Self-assembled RNA interference microsponges for efficient siRNA delivery[J]. NATURE MATERIALS, 2012, 11(4):316-322.
