Five steps to a gene edited plant

1

What trait do we want to change?

Scientists interested in altering a trait in a plant look at many different varieties of that plant to see what natural variation exists. Plant breeders maintain large germplasm collections — libraries of individuals representing the variety of genetic differences found in nature — to ensure access to the full diversity of the species.

If a trait, like blue flowers or star-shaped fruit, exists in a species naturally, you’re likely to be able to create it through gene editing, potentially much faster than if you used a traditional breeding approach. Gene editing allows scientists to make very simple changes to the existing DNA sequence of an organism to create a new version of an existing gene. This may result in a very different version of the trait to that of the original individual, but mirrors a change that could occur through natural mutation. The main advantage is the ability to bring one specific trait into an otherwise elite plant without many rounds of traditional breeding to remove unwanted changes.

Gene editing is a new genetic technology where an organism’s DNA can be modified at an exact point in its genetic code. As well as offering the ability to make precise genetic changes, the technique also does not necessarily involve the addition of DNA from another organism.

The most commonly used gene editing technology is the CRISPR-Cas system, a natural bacterial process that has been adapted for use as a genome editing tool in other organisms. Emmanuelle Charpentier and Jennifer Doudna, the scientists who developed the method, were awarded the Nobel Prize in Chemistry in 2020 for this discovery. Over the past decade, scientists around the world have been learning how to use the technique and fine-tune it in their organism of choice.

Gene editing is currently classified as genetic modification in New Zealand, but many countries are passing new regulations specifically for gene edited crops. Scientists around the world are now finding answers to the five questions that need to be addressed in creating a gene edited plant for commercial use.

Disease resistance in plants is sometimes conferred by a particular version of a single gene. The resistant version may exist in the wild relative but was not needed when breeding the cultivated crop, perhaps because of a lack of disease pressure in the growing region. A cross with the wild relative would introduce the resistant gene into some of the offspring, but would also mix in many thousands of unknown and unwanted versions of genes as well. It might take six or more rounds of breeding to get an elite cultivar back again. In perennial fruit crops, each round of breeding might take five or more years, making this a very slow process. With gene editing, this could be reduced to a single round by changing the gene from the susceptible to the resistant version directly in the elite cultivar.

2Do we know the gene(s) for that trait?

To be able to use gene editing to alter a trait, you need to know a great deal about how it is controlled at the genetic level. Some traits are controlled by a single gene, others by a network of genes and by influences from the environment.

For example, human height is controlled by a combination of more than 700 genes, with some influence from environmental factors like nutrition.

Gene editing involves programming the CRISPR-Cas system to seek out and make a change to a specific gene that controls the trait of interest. That means scientists need to have a deep understanding of the trait, the gene they wish to edit, its DNA sequence, how it is controlled and how it interacts with other genes in the plant. Only with all this information can scientists programme the CRISPR-Cas to target a specific DNA sequence within the gene and, with any certainty, alter only that gene and the associated trait.

3

Is there freedom to operate?

Scientific organisations have been patenting genes and DNA sequences since the 1970s, although some countries, like the USA, have changed their rules for gene patenting in recent years. Holding the patent on a gene means that no one else can work with it to create a commercial product without your permission for around 20 years (depending on the rules of the country where it’s been patented).

Therefore scientists may be limited to working with genes that they or their organisation have already patented, that haven’t been patented by anyone yet, that are already in the public domain, or where they can obtain permission from the patent holder.

There are also limitations on using CRISPR-Cas because of its ownership. Scientists can use the CRISPR-Cas technology for research purposes if they have a research licence, but their results can’t be commercialised without an additional, often costly, commercial licence. The terms of these agreements are negotiated with the patent holders, who can decide who to issue licences to, for what purposes, in which regions, and at what cost.

4

Do we know how to edit the plant?

Most of the time, scientists need every cell of the adult plant to contain the edited version of the gene to cause the desired trait change. This involves taking a single cell from an elite donor plant; getting the CRISPR-Cas machinery into that cell so it can edit the DNA sequence; growing the single edited cell up into a full plant; and checking the plant has the required edit and that no other unwanted changes have occurred during the process.

Plant cells are harder to edit than animal cells. Because of the structure of plant cells, the CRISPR-Cas machinery currently has to be introduced into the cell via genetic modification: scientists are looking for a way around this gene-modification step, as it usually leaves DNA from the CRISPR-Cas machinery in the plant cell.

Creating a whole plant from a single cell is also a challenge. A plant cell can be grown into a full plant using tissue culture, but there isn’t a one-size-fits-all process. Different plants, and in some species different varieties, require different tissue culture regimes, and it may take many years of experimentation to find one that works.

5 Does the edited plant perform well agronomically?

Even with all the information available to them, scientists can’t guarantee that a plant taken out of the lab will perform well in the field or orchard. Plants are very sensitive to their environment and changing one gene — whether through natural mutation or through gene editing — can have an impact on how a plant behaves in a production setting.

If a gene-edited plant were to be selected as a potential commercial variety, it would then need to enter the pipeline of growing trials used for all new varieties to ensure it had all the characteristics required for commercial success.

The need for regulation & stewardship

Genetic technologies offer benefits for food production, particularly in allowing scientists to deliver at a faster rate the new varieties that address some of the agrifood sector’s most pressing issues, such as climate change adaptation and resistance to new pests and diseases. However, there is still a requirement for ensuring the technologies are used appropriately, and that the varieties offer the same, or better, outcomes for consumers and producers. Across the world, regulations are changing and it’s important that altered regulations support both scientific advancement and consumer safety. Regulation based on the outcome of breeding programmes, regardless of the technologies used, is likely to offer both. However, there are also social, cultural and economic factors to be considered in introducing any new technology. It is important that all aspects of the debate are considered, to ensure that the deployment of gene technologies in a commercial setting delivers positive impacts for society.