New discovery challenges old assumptions about how plant cells stick together

- You did your PhD in Stéphane Verger’s research group at UPSC focussing on cell-cell adhesion in plants. How led you to join Stéphane’s group and focus on this research topic?

Stéphane and I met almost eight years ago when I was doing an internship in the lab of Olivier Hamant in Lyon where Stéphane was a postdoc. We worked together for nine months, and I really enjoyed it. When I was looking for a PhD, I also contacted him here in Umeå. The first think he told me was to please look at the map before you decide. I did not do that, but I do not regret that I came to Umeå and joined Stéphane’s group. I am his first PhD student, and it was a tough, long and emotional journey but I am very happy that I did my PhD with him. The decision to come to Umeå was one of the game changers of my life and UPSC is somehow my home now. I will miss it when I move on now.  

- What is meant by cell-cell adhesion and why is it important for plants?

Cell-cell adhesion is a very fundamental feature of multicellular organisms. When it comes to plants it is probably even more important – and I am not saying it just because I have worked now five years on this topic. Plant cells have a huge turgor pressure inside that presses the cell membrane outwards against its rigid cell wall. Still, the cells need to be connected and stay together to keep the tissue integer and that is what is achieved by cell-cell adhesion. There would be no multicellular organism without cell-cell adhesion. It not only keeps the tissue intact but also serves as a kind of barrier for example against pathogen attacks. 

- When summarising your thesis, what do you consider as the major outcome? 

In textbooks, it is written that the middle lamella, a layer between cell walls of different cells, is the glue that keeps the cells together, but we could show now that it is not like this. We identified two specific cell wall sites where cells are kept together. These sites are the places where cells are most at risk of being pulled apart and the cell wall at these sites is especially reinforced. When we tried to separate cells, these sites were always the sites that ruptured last. One of the biggest problems was the lack of proper tools but I managed to develop two different techniques to really study cell-cell adhesion in plants.

- Were there any results that were unexpected or astonishing to you?

Yes, there is one and I still do not understand it. When I grew seedlings on medium with one percent sucrose, which is a common concentration, I realised that the seedlings develop cell wall defects. It was at the beginning of my PhD, and I got very excited when I discovered this. I continued to study it as a side project, but it became now my new obsession because I still do not fully understand it. Plant cell walls are full of sugars. Why should external sucrose have such an effect? We know that sucrose is a unique and versatile molecule. It can serve as metabolite, delivering energy but also as signalling molecule. We could show that it regulates cell adhesion, but we still do not understand exactly how. 

- Did you face any challenges that you had to overcome during your PhD and that you would like to share with us?

From my point of view, the PhD itself is a challenge day by day. There are things that I had to overcome - problems with plants, techniques - and I had to find the best sample preparation method for transmission electron microscopy which was a huge challenge that took quite some time to solve. I think these challenges are somehow expected when you do a PhD, but I had to face also unexpected personal challenges that affected my PhD life a lot. I had to reformulate the idea why I do my PhD which was in the same way a good and refreshing moment. I have learned a lot about myself and feel now that I am a totally different person than five years ago. Even though it was tough, I am very grateful for this experience. 

- Nearing now the end of your PhD thesis, what are your next plans? 

I decided to continue in academia and do a postdoc to see if I really want to become an independent researcher. I love doing science - especially microscopy – but I am not exactly sure if I want to become a group leader. So, I plan to take one more step in academia to be sure. I will try to apply for a grant and are looking for postdoc opportunities. Already my PhD project was at the section between biology, physics and modelling but I focussed mainly on the biology part. Now, I would like to learn more about the other parts and challenge how I see biology.