Agrobacterium-mediated plant genetic transformation – an overview

Plants are, without a question, a crucial natural resource for human life. As a result, throughout history, we have attempted to improve both the yield and quality of cultivated plants. We have seen the evolution of genetic engineering technologies, particularly in the last several decades, as a reaction to the biotic and abiotic stressors that plants face.

Transgenic plants are now possible thanks to these technologies. You have probably heard of them because they have been a hot topic, and you might be curious as to how scientists "create" them. Agrobacterium-mediated transformation (AMT) is one of the most used methods. It has made it possible to advance valuable crops and their varieties for agriculture, pharmaceutical, and other plant-based industries.

Let us learn more about this technique and what it can offer!

Agrobacterium, a natural genetic engineer

Over 100 years ago in the United States, Smith and Townsed (1907) identified a bacterium as the causative agent of crown gall disease in plants. Agrobacterium, as it is now called, has transformed plant molecular genetics and spawned a whole new industry dedicated to plant genetic modification. But what exactly is Agrobacterium?

Agrobacterium is a plant pathogenic bacteria genus found in soil. However, the word Agrobacterium is commonly used to refer to the most prevalent species, Agrobacterium tumefaciens. It naturally infects wound-prone plants, generating tumorous plant growth known as crown galls.

You may be wondering why we employ Agrobacterium since it is a "bad" bacterium for plants as it causes a disease. For this, let us first understand how it infects the plants.

When a plant has a wound, it generates some molecules that serve as a signal to the bacterium. Then, it recognizes the signal and attaches to the plant. Agrobacterium has a plasmid (a small circular DNA molecule) that contains a T-DNA segment. This segment is transferred to plant cells and contains the information necessary for them to produce tumor-inducing hormones and molecules.

To put it another way, the bacteria can transfer and integrate genetic information into the plant, allowing it to be expressed. This unique technique is what makes Agrobacterium such an excellent genetic engineer. Scientists discovered that we may remove T-DNA to get safe strains and replace it with any gene of interest via research! This enabled us to apply the Agrobacterium process without harming the plant, making it the most popular plant transformation method to date.

How to genetically transform plants?

We produce transgenic plants when we use Agrobacterium as a vehicle/vector to transfer a gene of interest into a target plant! It refers to plants that carry genes from other plant species in their genome.

Protocols for making the procedure work in practically every crop have been published. However, the AMT (Agrobacterium-mediated transformation) process is a very complicated and evolved mechanism. In practice, there are six critical steps:

1. Explant preparation;
2. Agrobacterium preparation:
3. Infection;
4. Co-cultivation;
5. Selection and regeneration; and
6. Rooting.

It may appear simple, but the key point about the technique's intricacy is that it is impacted by a variety of factors. Explant type and age, Agrobacterium strain, and co-cultivation variables like pH and temperature are among them. If you want to learn more about the process in depth, stay tuned for future articles!

Tissue culture, our ally!

The purpose of Agrobacterium-mediated transformation is to get viable transgenic plants containing desired genes. With this in mind, not only successful T-DNA transfer and integration into the plant genome, but also the selection of transformed explants and regeneration of complete transgenic plants, are critical.

So, how do we achieve our final goal? Tissue culture is the answer! When performing genetic transformation, it is frequently necessary to establish a reliable in vitro plant regeneration procedure.

Why is that? Because tissue culture is an efficient strategy for the fast production of uniform, virus-free, good-quality transgenic plants. For Agrobacterium-mediated transformation, techniques like somatic embryogenesis, shoot organogenesis, and cell suspensions (for recalcitrant species like bananas) are predominantly used.

Why transform plants using Agrobacterium?

Climate change and population growth have necessitated the development of enhanced crops with improved features such as yield, disease resistance, stress tolerance, and so on. Although conventional techniques of plant breeding have had some success, they do not fulfill the demands of today because they require more time, labor, and ambiguity of results. Therefore, Agrobacterium-mediated genetic transformation and in vitro plant tissue culture techniques have become essential tools for improving plant performance for a variety of important traits. This approach has the following advantages:

• Most effective and well-known laboratory method;
• Transgene stability in the genome;
• Efficient transformation;
• Minimal equipment and facilities required;
• Easy to set up;
• Minimal DNA rearrangements; and
• Varieties are obtained in a short time.

Moreover, it is easy to use, practical, and relatively inexpensive. So, it is not surprising that this technique is preferred over other transformation systems.

Applications

To date, transgenic plants have been gradually released into commercial products. Even you might have tasted some of them!

• Virus-resistant plum that is on the horizon to be commercially released;
• Non-browning apples that are in the stores; and
• Golden rice fortified with provitamin A (β-carotene). (This is a well-known example of the use of this technology to produce better crops with improved nutritional qualities.)

Agrobacterium-mediated gene transfer is a strong tool for producing secondary metabolites and recombinant proteins (namely, molecular farming), phytoremediation and pharmaceuticals, crop improvement, targeted gene knockdown, and the development of biotic and abiotic resistant transgenic plants.

This approach may also be used to study fundamental plant genetics, gene function, and editing. If you want to know more about this and other interesting topics, stay tuned to this space!

By Valeria Francis | 8th November 2022

Valeria Franco is from Colombia, the land of orchids. She is a focused and passionate biologist who specializes in biotechnology and molecular biology. Valeria has prior laboratory and research experience. She is presently employed as a content creator at Lab Associates and is always looking for new challenges. Valeria is enthusiastic in plant science themes and reading as a tool for lifelong learning. Her hobbies include studying foreign languages, traveling, and archery.

References

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