The Groundcherry and CRISPR Manipulation of Genes

The groundcherry (Physalis pruinosa) is an interesting plant with a flavourful fruit and potential benefits for humans. Unfortunately, it has problems as an agricultural crop. It isn't easy to grow and the fruit tends to drop to the ground before it's ripe. This tendency and the small size of the fruit gave the plant its common name. A team of U.S. researchers has successfully altered some of the features of the plant with a method of gene editing known as CRISPR. This could be helpful in creating a new food crop for humans.



Photo credit: Physalis pruinosa by Carstor, CC BY-SA 3.0 license

The Groundcherry Plant

I've never tasted a groundcherry, but it sounds like an intriguing fruit. The flavour is said to be both sweet and sour and to contain elements of pineapple, vanilla, and tomato. It's not as sweet as some popular fruits, however. The smell of the fruit is said to be "intoxicating."

The groundcherry plant belongs to the family Solanaceae, which is commonly known as the nightshade family. Tomatoes also belong to this family. Some other members of the genus Physalis are known as groundcherries as well, so when reading about the fruit it's important to check the species that is being discussed. The members of the genus are known for the papery husk or capsule that partially or completely surrounds the fruit. The capsule is derived from the calyx of the flower. A popular ornamental plant in the genus (Physalis alkekengi) is known as the Chinese lantern plant. Its orange capsules are attractive and much admired.



Photo credit: Chinese lantern plant by Shu Suehiro, CC BY 3.0 license

A Basic Introduction to CRISPR

CRISPR technology arose from an observation in certain bacteria. The bacteria had developed a method to cut and destroy strands of viral DNA (deoxyribonucleic acid) that invaded the cell. The process involved a bacterial enzyme known as Cas9. A piece of bacterial RNA (ribonucleic acid) joined to a specific location on the viral DNA and then the enzyme broke up the DNA.

The bacterial system was reminiscent of own immune system because it "remembered" the virus attack. If it was infected by that type of virus again, it produced the appropriate RNA to find and bind to the correct region on the DNA so that Cas-9 could break it up.

Researchers released that they could use a similar technique to remove a section of an organism's DNA in a specific location and then insert a gene of their choice. A gene is a section of DNA that codes for a particular protein. The code is how genes control the characteristics of an organism.

Scientists create a piece of guide RNA that binds to the area of DNA that is of interest. The Cas-9 enzyme then breaks the DNA in that area. The scientists use the cell's DNA repair mechanism to insert the desired genetic material into the broken area and repair the break.

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. The gene-editing technique is sometimes referred to as CRISPR-Cas 9. Understandably, the process is worrying some people because it appears to be such a precise and efficient way to alter the genes of an organism. Genetic modification of any kind requires great care. It could have great benefits if done responsibly, however.

Modifying the Groundcherry Genome

By using CRISPR and their knowledge of the tomato genome, the researchers have created groundcherry plants that have a more compact form (and therefore are more manageable by growers) and that produce fruits in clusters instead of singly. In addition, they have been able to create larger and denser fruits. They haven't yet modified the taste, but that's their next goal.

Plant growers can use selective plant breeding techniques to develop desirable features in cultivated plants. Changes that make the groundcherry a better crop for humans could take a very long time, however. CRISPR is much faster and should produce new fruit to eat quite soon.

Photo credit: Flower of Physalis coztomatl by Carstor, CC BY-SA 3.0 license

Feeding Hungry People

At the moment, the groundcherry is said to be an orphan crop. An orphan crop is cultivated on a very small scale or is used for subsistence. Problems such as a low yield or quick decay once it's harvested prevent it from becoming a mainstream crop. This is a shame with respect to the groundcherry because it's said to be a nutritious fruit.

The groundcherry research could be important. A professor of nutrition at New York University is impressed by the recent research, but she points out that producing larger quantities of nutritious food is not the only requirement for feeding the world. Problems such as the existence of war and the lack of transportation to move food crops to where they are required need to be solved. Preservation of food during transport and before distribution is also a concern.

As the Earth's population grows and the need for quickly grown and nutritious plants increases in order to feed hungry people, CRISPR could become very important in improving crops, whether we like it or not. 

References

CRISPR basics from John Hopkins School of Medicine

What are genome editing and CRISPR-Cas 9? from the U.S. National Library of Medicine, National Institutes of Health (NIH)

Groundcherries: A modified fruit you may want to try from CNN

An orphan crop that could be the next strawberry from the Howard Hughes Medical Institute