1. Soil Loss: Challenges and Solutions

Throughout history, soil loss has had far-reaching impacts on both the environment and human well-being. Environmental degradation results from the loss of vital organic matter, disrupting carbon cycles and nutrient provision, while human populations suffer reduced agricultural yields and the specter of starvation. Contemporary strategies to counter soil loss involve government policies limiting over-excavation of fertile soil, contour farming to mitigate runoff, and textile-based soil stabilization.

2. Plant Cultivation: Primary Solution, Low Seed Germination

The prevalent approach revolves around planting cover crops or promoting reforestation, reintroducing vegetation for soil stabilization and increased organic matter. A significant hurdle, however, is the limited success of seeds in germinating in infertile soil, leading to slow growth rates for these protective plants.

3. IAA's Role and Challenges: Paving the Way for a Novel Solution

Our team seeks to address this challenge by supplementing plants with extra IAA (Indole-3-Acetic Acid), a natural plant growth hormone. As existing biochemical methods remain in development, an innovative and efficient approach is required to harness the potential of IAA effectively. Thus, our team's primary focus shifts towards creating a novel method to provide plants with additional IAA, enabling growth even in impoverished soil.

4. Unpacking IAA

Indole-3-Acetic Acid (IAA) serves as a natural plant growth hormone, vital for seed germination and overall plant development. However, despite its potential benefits, IAA faces challenges in current applications, particularly in adverse soil conditions, necessitating a fresh approach for more effective use.

In order to achieve our goal, we have introduced three distinct systems in our engineered E. Coli strains that will produce the IAA that the plants need: an IAA production system, an EPS production system, and a conditional apoptosis system.

These systems serve the purpose of actually producing excess IAA, forming a biological crust to avoid seed runoff, and prohibiting biocontamination, respectively.

The IAM Pathway (Figure 1).For our IAA production system, we have selected the IAM pathway, which involves the insertion of two genes, iaaM and iaaH. These genes are derived from Pseudomonas savastanoi, a bacterium known for its IAA production capabilities. The iaaM gene codes for the IaaM enzyme, responsible for converting tryptophan into Indole-3-Acetamind (IAM), while the iaaH gene codes for the IaaH enzyme, which further transforms IAM into IAA. This pathway is notable for its efficiency, requiring only two enzymes and one intermediate product to swiftly convert tryptophan into IAA.

The GaiU Pathway (Figure 2)For our EPS production system, we have opted for a streamlined approach involving a single enzyme, GaiU. We introduced the GaiU gene, which encodes the GaiU enzyme, capable of converting UDP-glucose to UDP-glucose pyrophosphate. Subsequently, the product of this enzymatic reaction can undergo intracellular transformations to yield EPS. The presence of EPS contributes to the formation of a biocrust, enhancing soil adhesiveness and mitigating the issue of seed displacement in impoverished soils, even during light rainfall events.

The MazF Approach (Figure 3).To induce cellular apoptosis effectively, we introduced the mazF gene under the control of the arabinose promoter into E. coli strains. This gene encodes the mazF enzyme, a stable protein toxin that functions by cleaving mRNA chains, thereby inhibiting DNA expression within the cell and ultimately leading to cell death. The development of this system is imperative due to our utilization of genetically engineered bacterial strains within the environment. Preventing genetic contamination caused by these engineered genes is a paramount concern, hence the implementation of this safeguarding mechanism.

Our innovative approach combines three interconnected systems, working in unison to ensure an effective IAA production cycle, provide application support, and institute programmed apoptosis to safeguard against gene contamination.

During our manufacturing process, we employed gene editing techniques to seamlessly integrate three vital systems into the genomes of E. coli: the plant hormone (IAA) production system, the exopolysaccharide (EPS) production system, and the cell suicide system. These three systems operate in harmony, resulting in the production of IAA, the stabilization of soil structure, and the controlled release of IAA when needed. The end product exhibits a concentric structure, with the seeds centrally located, followed by freeze-dried bacterial strain powder, an intermediate hydrogel layer, and the outermost hydrogel layer infused with arabinose. (Figure 4)

As the plants grow and reach this outer layer, arabinose triggers cellular apoptosis, prompting the engineered bacterial strains to self-destruct and thus preventing any potential biocontamination.（Figure 5）

Target User Group:

In human history, soil erosion has remained a critical issue, leading to ecosystem degradation due to the depletion of organic matter essential for carbon cycling and nutrient provision. It profoundly impacts agricultural yields and exacerbates issues like hunger. As a result, our primary user demographic comprises farmers in regions where ecosystems have suffered degradation.

Product Usage Guidelines:

Utilizing our products follows a straightforward process akin to traditional seed planting. First, prepare the soil by loosening it. Second, sow the seeds, either manually or using a specialized seeder. Third, lightly cover the seeds with soil after sowing. No need for excessive soil coverage. Fourth, ensure timely soil watering after completion. Fifth, apply fertilizer as needed. Lastly, patiently await seed germination and seedling growth, intervening as necessary for weed control and pest management.

Ensuring Biosafety:

We've implemented several enhancements to our initial version to mitigate the risk of potential biological leaks. As previously mentioned, to eliminate uncertainties, we've devised a cell suicide system (explained in detail earlier). The gene we've incorporated encodes the mazF enzyme, a stable protein toxin that severs mRNA strands, thus inhibiting DNA expression in cells and inducing cell death. Importantly, this process poses no environmental contamination risk post-cell death.

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