Blog - What does it mean to be alive?

Hee-Kyung Ahn, Royal Society University Research Fellow, recalls her grandmother's love of growing plants, and how this excited her own curiosity to study them.

My grandmother loved growing plants. Every little space in our home would be filled with plants in no time. But my favourite plants were the four o’clock flowers (Mirabilis jalapa). It was an annual plant back home in South Korea, because they couldn’t survive the harsh winters there. My grandmother showed me how to collect the seeds to plant them next year. Each four o’clock flowers had a different mix of yellow and magenta. It was fascinating to see the seeds I collected in the previous year make completely new pattern of flowers the next year. The individuality of each flowers made me appreciate how unique every single beings are. My grandmother’s house plants were how my curiosity to plants began.

Picture of the bud, flower, and fruit of Mirabilis jalapa. (Image credit: WikiCommons)

There was no question in taking biology as my undergraduate major. From my 2nd year as an undergraduate, I started working as a part-time research assistant in a plant molecular biology lab. I learned basic molecular biology skills, like preparing media, but also other lab works like filling out tip boxes and autoclaving. I guess I was a one-person media kitchen for the group. As years went on, I learned other techniques in plant molecular biology, knocking down or overexpressing genes and observing phenotypes. In my final year, I was harvesting one of the Arabidopsis transgenic lines I generated, and noticed that the seeds were bigger. I couldn’t believe my eyes! It was overexpressing one gene, but that seemed to make the plants grow faster, and also make the seeds bigger (Ahn et al. 2015). That’s when I knew I wanted to do a PhD in the lab.

My PhD project was to identify other genes potentially downstream of the gene our lab worked on, and then silencing them to see its phenotype. The gene I decided to work on was a chaperonin complex that seemed to work downstream of the original gene I worked on in mammals. These chaperonins are made of 8 different genes, but silencing one gene dissociates the whole chaperonin. And the outcome of lack of this chaperonin is lethality. These genes were so important that we couldn’t retrieve mutants, so we had to knock-down these genes, and even that was lethal to the plants (Ahn et al. 2019). It was fascinating. How can one gene do this? How can one protein complex be so important to keep cells alive?

When plant pathogens secrete proteins into plant cells, some of these proteins are recognized by intracellular immune receptors in the plant cells, and result in immediate cell death. We call this Hypersensitive Response (HR). It was known that the immune receptors associate with each other to make this cell death happen. To me, this was a brilliant example of the ‘emergent property’ in life. The sum of two components lead to greater results, but in this case, the result is cell death. I jumped onto the opportunity to work on HR and plant immunity for my postdoctoral research. Throughout my postdoc years, there have been amazing discoveries around the world where we could actually see the structures of these assembled immune receptor complexes (Wang et al. 2019). Yet, we still have a lot of questions. There are so many different types of immune receptors in plants that are bound to work differently. For example, we recently reported on immune receptors that only changes its shape a little bit to become active (Ahn et al. 2025). And because the outcome of carrying this protein complex around is cell death, this assembly is very tightly controlled, but we know little about how actually these protein complexes are kept under control.

Photo of 2 plants, one labelled control and the other, smaller, labelled CCT2 knockdown — When the amount of CCT2 genes are reduced, plants not only grow slower, but also cells in the young leaves start turning yellow and die. (Image credit: Hee-Kyung Ahn)

I feel I am very lucky to join IMPS as the Royal Society University Research Fellow, and to continue working on plant immune receptors and their assembly in cells. Colleagues at IMPS study various aspects of plant development, growth, and immunity that I am really looking forward to learn more about. Plant immunity is unique to plants, but how protein complexes assemble or are kept from assembling is a broader question that applies to all living cells. Can we find a simple rule of life from all the different ways immune receptors complexes assemble in cells? I also want to learn more about immunity in other plant species. Arabidopsis is my favorite plant, but it would be a huge missed opportunity to not study all the other fascinating plants in the world.

This post was written in loving memory of my grandmother, who passed away in January 2025.

Blog - What does it mean to be alive?

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