Our Global Food Security Is Threatened
Food is one of the most fundamental human needs. This need becomes even more substantial the more people live on earth. Currently, our agricultural industries feed 7.8 billion people and this number is estimated by the UN to likely increase to over 12 billion until the year 2100 [1]. Thus, it becomes apparent that crop losses pose a major threat to the health and safety of millions of people. This problem is further intensified by the limited cultivation area on our planet.
To prevent crop losses every year millions of tons of pesticides are used against insects, fungi and non-crop plants [2]. However, pesticides have detrimental side-effects on the environment by contaminating groundwater, soil, air and non-target organisms [3]. An increasing world population entails an increased need for crops, which leads to an elevated use of pesticides. Furthermore, pests (e.g. insects, microbes, fungi) can adapt to pesticides via evolutionary processes and render common pesticides useless.
Our team has made it its mission to counteract exactly these problems.
Just as all other crop plants, maize is threatened by a plethora of pathogens:
- Viruses:
Corn can be affected by many viruses, such as Maize dwarf mosaic virus or
Sugarcane mosaic virus (causing Maize dwarf mosaic), Maize streak virus (causing Maize streak), Maize chlorotic dwarf virus (causing Maize chlorotic dwarf) and many more [4].
- Bacteria: The majority of corn diseases are caused by fungi. However, some are caused by bacteria. Within the corn-growing area, the primary bacterial diseases are Holcus leaf spot, Goss’s Wilt, Stewart’s wilt, and bacterial stalk rot. Bacterial diseases generally enter the plant through wounds caused by insects, wind, hail, or blowing soil.
- Fungi: Magnaporthe oryzae and numerous other fungal species of several genera, such as Fusarium spp., Rhizoctonia spp., Pythium spp., Diplodia spp., Penicillium spp. and Trichoderma spp. are threatening harvests around the world. For example, fungi can cause seed rots and seedling blights in corn.
The Solution: Transcriptional Synchronisation
Pathogens are interacting with the cellular machinery of their hosts. Plants adapt to pathogen infections by using specific resistance mechanisms, which increase the production of certain types of proteins within the cells. Infection activates specific promoters in the plant genome leading to the expression of certain mRNAs of plant defence genes. Sometimes pathogens are able to reprogram cells to produce specific products they need, which is detrimental for the plant cell. We aim to synchronise the transcription of these mRNAs with a therapeutic output against pathogens.
Therefore, increased mRNA production due to pathogen infection is linked to an therapeutic output, so that further proliferation of the pathogen is automatically inhibited and the plant becomes resistant. siRNAs are known to counteract pathogens and used here as a therapeutic output. Our system is highly adaptable and can be adapted to the respective pathogen.
Features of our mechanism
Our approach combines several features, which are advantageous compared to other solutions:
- Universal applicability: The mechanism can be used in different plant models (monocotyledon, dicotyledon) and against every viral, microbial and fungal pathogen. It can be also used in all domains of life.
- Endogenous gene regulation: Instead of using synthetic regulatory elements, which can function unpredictably in different genetic contexts, our solution relies on endogenous regulatory elements and no additional regulation mechanism has to be introduced.
- Low metabolic burden: The system has a relatively low impact on the plant metabolism due to the natural regulation of the output, which is only expressed, if a pathogen infection occurs and doesn’t negatively influence growth and/or other cellular processes under normal conditions.
- Compact efficiency: Our mechanism can be synchronised with every desired gene of the crop. Synchronisation replaces traditional regulation mechanisms (constitutive promoters), making the overall mechanism more direct. The mechanism can further be expanded by creating operon-like structures in eukaryotes. Thus, more resistance genes can be brought more easily into a plant to make them more resilient. Thus, the overall number of modifications can be reduced by using natural gene regulation combined with operon-like structures, making the mechanism very compact and efficient.
- Evolutionary stability: The use of multiple inputs (synchronised endogenous genes) and multiple outputs (synthetic resistances) makes it virtually impossible for any pathogen to adapt to the synthetic resistances by evolutionary means.
- Development costs: The mechanism enables the introduction of multiple resistances in a more efficient and reliable way. Also, by denying pathogens to adapt to a plethora of resistances, resistant plants do not need to be designed multiple times. This decreases the overall costs of pathogen-resistant crop plants.
Outlook for 2021
After implementing a proof of concept in E. coli, the implementation of the mechanism is also planned in plants. In general, plants grow much slower than bacteria so the number of experiments which can be carried out is limited. Also, the mechanism is more complex in eukaryotes. This is the reason for the initial conduction of the proof of concept in E. coli.
The plan is to use Zea mays for a transient transformation with our construct and Arabidopsis thaliana for a stable transformation. For these plants, two different vectors will be used and an insert which can be introduced in both plant species will be designed. The reason Zea mays and Arabidopsis thaliana were chosen is to test the construct in monocotyledon plants and as well in dicotyledon plants.
References
[1] Online source: Federal Republic of Germany, accessed 27th October 2020, https://population.un.org/wpp/Graphs/Probabilistic/POP/TOT/900
[2] Online source: Max Roser (2019) - "Pesticides", accessed 27th October 2020, https://ourworldindata.org/pesticides
[3] Aktar MW, Sengupta D, Chowdhury A. Impact of pesticides use in agriculture: their benefits and hazards. Interdiscip Toxicol. 2009;2(1):1-12. doi:10.2478/v10102-009-0001-7.
[4] Redinbaugh MG, Zambrano JL. Control of virus diseases in maize. Adv Virus Res. 2014;90:391-429. doi: 10.1016/B978-0-12-801246-8.00008-1. PMID: 25410107.
