BACKGROUND
Agriculture is one of the most important sectors that drive economies around the world. It plays a crucial role in providing the necessary food and nutritional requirements for the growing human population.
Crop diseases, pests, and weeds are the three major challenges in maintaining a stable agricultural ecosystem, where disease outbreaks pose significant risks to global food security and environmental sustainability, leading to loss of primary productivity and biodiversity.Despite the extensive use of pesticides, disease-related crop losses in China still constitute a significant proportion of the country's total annual production, particularly for economic crops. This has serious negative impacts on the affected region's environment and social and economic conditions.
Although traditional pesticides have alleviated the challenges facing agricultural production to some extent, they have also brought many problems.
Traditional chemical pesticides in agriculture pose numerous hazards. They can harm human health, as well as contaminate the environment by drifting in the air, leaching into soil and water, harming beneficial organisms and biodiversity. Overuse leads to pesticide resistance, reducing their effectiveness and requiring more pesticides. This increases costs for farmers and impacts productivity. Additionally, pesticide residues on crops can limit market access and profitability.
Therefore, seeking safer, more efficient, and sustainable alternatives is an important issue currently facing agriculture.
| Plant Diseases | Pathogenic Fungi | Chemical Pesticides |
|---|---|---|
| Rice blast | Pyricularia oryzae | Carbendazim, Azoxystrobin, etc. |
| Rice sheath blight | Rhizoctonia solani | Carbendazim, Difenoconazole, etc. |
| Wheat blight disease | Fusarium spp. | Propiconazole, Carbendazim, etc. |
| Wheat stripe rust | Puccinia striiformis | Propiconazole, Carbendazim, etc. |
| Wheat powdery mildew | Blumeria graminis | Propiconazole, Carbendazim, etc. |
| Cercospora zeae-maydis | Cerospora spp. | Carbendazim, Azoxystrobin, etc. |
| Potato late blight | Phytophthora infestans | Mancozeb, Chlortetracycline Hydrochloride, etc. |
| Powdery mildew of Chinese Cabbage | Erysiphe cruciferarum | Carbendazim, Azoxystrobin, etc. |
| Panama disease of banana | Fusarium oxysporum | Chlorothalonil, etc. |
| Strawberry powdery mildew | Sphaerotheca aphanis | Carbendazim, Azoxystrobin, etc. |
PROJECTDESIGN
This year, students from ZJU-China came up with the idea of using synthetic biology to link artificially synthesized gene pathways with plant's innate immune pathways. The goal is to develop a safer and more efficient biological pesticide that would enable plants to have biopesticide products similar to human vaccines.
Therefore, Flora Sentinel has made her debut! We have designed a long stranded RNA that can function within plant cells. The core fragment can be translated into a modified version of immunoprotein, possessing efficient and targeted resistance against specific pathogens. And inspired by the concept of RNA vaccines, we have equipped it with a platform that enables the RNA to move and multiply within plant tissue. By utilizing Agrobacterium tumefaciens as a reliable engineering chassis, it can be formulated into pesticide formulations, making it easy for farmers to use.
We strongly believe that clean and effective biopesticides will be a major focus of future research. We envision a future where more Flora Sentinels will protect fields under human guidance, ensuring flourishing crops and abundant harvests for the world.
For more information on design, please click on the link.
THEORETICALBASIS
Plant Immune System
Plants possess a robust innate immune system, comprising of PTI and ETI pathways. PTI relies on cell surface receptor recognition, while ETI relies on intracellular proteins such as NLR. Pathogens often secrete effectors to hinder PTI, making ETI crucial for long-term plant defense and integration of both pathways. Thus, our project primarily investigates NLR and its role in the ETI pathway.
NLR Proteins
The NLR (Nucleotide-binding domain and Leucine-rich Repeat) family is a protein family that exists widely in plant cells. They play a crucial role in the immune system of organisms by recognizing and defending against the invasion of parasites, viruses, and bacteria.
They are receptors in plant cells that detect pathogen effectors and initiate immune responses. They can be divided into receptor NLR and signaling NLR. Receptor NLR recognizes effectors, while signaling NLR triggers immune responses. The NLR structure consists of N-terminal, NB-ARC, and LRR domains. Each domain has the ability to identify specific effectors.
Hence, our project primarily focuses on the examination of an uncommonly observed binding sequence on NLR, referred to as the integrated decoy, commonly abbreviated as the ID sequence.
The ID Sequence
The integrated decoy sequence is not found in the NLR of every plant. It is not very homologous between species, and can locate on different locations on the NLR.
The role of this sequence is already written in its name - a "decoy". The structure of this sequence is extremely similar to the target protein of the pathogenic effector, allowing it to bind effectors in a competitive manner, which makes it an effective identification method for immune responses. This simple but specific identification mechanism implies the ability for platform and scalability, which is exactly what we are looking for in a project.
Previous Studies
Researchers from the University of East Anglia in the UK have devised a novel approach to enhance plant disease resistance using animal antibodies. However, the current ID sequence lacks tight binding and specificity. Therefore, our proposed solution involves substituting the ID sequence with a specially engineered nanobody capable of precise effector binding, while still retaining the ability to recruit signaling NLR and trigger downstream immune responses.
References
[1] Yu X, Feng B, He P, Shan L. From Chaos to Harmony: Responses and Signaling upon Microbial Pattern Recognition. Annu Rev Phytopathol. 2017 Aug 4;55:109-137. doi: 10.1146/annurev-phyto-080516-035649. Epub 2017 May 19. PMID: 28525309; PMCID: PMC6240913.
[2] Yuan M, Ngou BPM, Ding P, Xin XF. PTI-ETI crosstalk: an integrative view of plant immunity. Curr Opin Plant Biol. 2021 Aug;62:102030. doi: 10.1016/j.pbi.2021.102030. Epub 2021 Mar 5. PMID: 33684883.
[3] Cesari S, Bernoux M, Moncuquet P, Kroj T, Dodds PN. A novel conserved mechanism for plant NLR protein pairs: the "integrated decoy" hypothesis. Front Plant Sci. 2014 Nov 25;5:606. doi: 10.3389/fpls.2014.00606. PMID: 25506347; PMCID: PMC4246468.
[4] Kourelis J, Marchal C, Posbeyikian A, Harant A, Kamoun S. NLR immune receptor-nanobody fusions confer plant disease resistance. Science. 2023 Mar 3;379(6635):934-939. doi: 10.1126/science.abn4116. Epub 2023 Mar 2. PMID: 36862785.
