An Interview with Leonie Luginbuehl: Asking the “Carbon Questions” in Plant-fungal Symbioses

Leonie Luginbuehl (X: @l_luginbuehl) is an Assistant Professor at the University of Cambridge in the UK. Prior to her current position, she was a PhD student in the lab of Prof. Giles Oldroyd at the John Innes Centre in Norwich, where she discovered the role of the transcription factor RAM1 in regulating the exchange of nutrients between plants and their symbiotic fungi. She then worked as a Herchel Smith Postdoctoral Research Fellow in the lab of Prof. Julian Hibberd at the University of Cambridge, where she investigated the cell type specific regulation of gene expression in photosynthesis and the evolution of the C₄ pathway.

The research in her group is centred around understanding carbon allocation in plants during the symbiosis with beneficial fungi. To answer their questions, Leonie and her team employ a wide range of techniques, from microscopy to single cell RNA sequencing and isotope labelling. By doing so, they hope to gain a better understanding of the carbon costs associated with symbioses and to discover under which conditions these interactions truly benefit the plant. Their pioneering research could potentially lead to a better exploitation of beneficial microbes in agriculture, boosting plant nutrition and yield.

 

Carlo Pasini: Leonie, where does your fascination with plant biology come from? How did that develop into your current research?

Leonie Luginbuehl: Before going to University, I wasn’t particularly interested in biology and never thought I’d end up working as a biologist. However, I became completely captivated with biology when I first learned about the mechanisms of transcription during my undergraduate degree. It is such a fundamental and elegant yet complex process. At that time I was planning to graduate in pharmacy. Then, an inspiring series of lectures by Prof. Thomas Boller opened the world of plant biology to me. I was fascinated by the possibility of studying plants through the lens of molecular biology. I ended up graduating in both biology and pharmacy, but for my Master’s degree, I shifted my focus solely to plant biology and worked on the transcriptional regulation of plant metabolism and development in the lab of Prof. Sam Zeeman. For my PhD I switched topics to investigate how plants reprogramme their roots to accommodate beneficial fungi. I started studying the role of the transcription factor RAM1 in this process. Our findings revealed that RAM1 controls the delivery of fixed carbon from the plant host to mycorrhizal fungi, and that this happens in the form of lipids. Mycorrhizal fungi are unable to synthesise their own lipids and so depend entirely on the plant for the provision of these essential metabolites. This brought me back to my previous work on primary metabolism and got me interested in how carbon is assimilated in source tissues such as leaves before being allocated to different sink tissues. I applied for a postdoctoral fellowship in the field of photosynthesis, and went on to investigate the cell-specific regulation of photosynthesis gene expression in C₃ and C₄ plants. Since starting my own research group one and a half years ago, I have moved back to the field of symbiosis to ask how carbon allocation to mycorrhizal fungi is regulated in plants. What I’ve always found most exciting are questions that lie at the intersection between different fields of plant biology, such as plant metabolism and the interactions between plants and microbes. I enjoy tackling these questions using interdisciplinary approaches.

 

Carlo: How would you summarize the current research topics of your group?

Leonie: Our research encompasses different aspects of plant biology, from signal exchange between plants and symbiotic fungi to plant physiology and the regulation of gene expression. Our focus is on understanding the nutrient trade between plants and their fungal symbionts, with an emphasis on the carbon costs associated with beneficial symbioses. Plants allocate as much as 20% of their assimilated carbon to mycorrhizal fungi in the soil in exchange for mineral nutrients. This is a huge cost for the plant. We want to understand how resource allocation is regulated during symbiosis at different scales, from single root cells to the whole plant system. What I find particularly fascinating are the mechanisms that allow communication and coordination between shoots, the site of carbon fixation, and roots, the site of carbon use and transfer to mycorrhizal fungi. This also implies other questions, for example how external factors such as nutrient availability and light affect the exchange of nutrients in the root and the importance of fungal signalling molecules in regulating these processes.

 

Carlo: What techniques do you employ to explore these questions?

Leonie: It really depends on the specific question we want to ask. We go from very simple staining techniques that allow us to observe the fungal structures associated with plant roots under the microscope, to more nuanced and technically challenging experiments like single cell RNA sequencing. On the metabolic side, we perform both ¹³C- and ¹⁴C- labelling experiments to trace the carbon flux between the plant and mycorrhizal fungi. We also look at physiological parameters in the shoot, such as chlorophyll fluorescence and carbon assimilation. Moreover, because we work with the model plants rice and Medicago truncatula, we spend a considerable amount of time on the genetic manipulation of these plants.

 

Carlo: Any facts related to your research which you find particularly interesting?

Leonie: A recent study has estimated that the amount of fixed carbon transferred from terrestrial plants to the mycorrhizal network in the soil each year is equivalent to more than 30% of the global CO₂ emissions from fossil fuels. To me, this illustrates how the questions we investigate, which I like to call the “carbon questions”, have implications not just at the level of individual plants and fungi, but also on a global scale.

 

Carlo: Where do you see your field going in the future? And your own research?

Leonie: I think that in the field of plant-microbe interactions, the focus is shifting from the foundational biological discoveries to their possible applications in agriculture. There is a lot of interest in using beneficial microbes to boost plant nutrition and productivity. However, we still understand very little about the role of each microbial species in this context and the benefits these microbes can bring to crop plants under different conditions. More closely related to our own research, we are still lacking a comprehensive view of how carbon and other resources are distributed across the plant in a coordinated manner, and how the communication between different plant tissues influences these decisions. Engineering crops to boost photosynthesis will not be an effective strategy unless the products of carbon assimilation are targeted to the right sinks, whether these are beneficial microbes that associate with roots or developing seeds during reproduction. Our ability to answer these questions is limited by technical challenges such as those associated with tracing carbon within the plant. Primary metabolites are constantly interconverted in the cells and visualising or quantifying them either requires sophisticated equipment or challenging experimental setups. NanoSIMS (Nanoscale secondary ion mass spectrometry) has been an interesting development in recent years, but it is limited in the scale of the measurements, which are performed on a single-cell level rather than the whole plant. Technical advances in this area will be of vital importance to the development of the field.

 

Carlo: Any other scientific interests you would like to pursue?

Leonie: In addition to answering fundamental questions in plant biology, I am really keen to translate my scientific expertise and interests into new solutions for precision agriculture. Gene expression profiling of plants could lead to the development of novel biomarkers which can detect the onset of plant stresses, such as the presence of pests, drought stress, and nutrient deficiencies at a very early stage. However, the potential of these techniques has not yet been realized. That is why I have recently co-founded a start-up called Crop Diagnostix. As a team of plant biologists, machine learning scientists, and business partners, we aim to develop such biomarkers and make these available to farmers. We are currently fundraising and we hope to be up and running within the next few months!

 

Carlo: On a more personal note, what are your favourite and least favourite parts of the job?

Leonie: The people I work with are my favourite part of the job. I love discussing science with my lab members, coming up with new ideas for experiments, and sharing our excitement for research! I also really enjoy teaching and find the interactions I have with my students incredibly rewarding. The most challenging part for me at the moment is juggling all the different roles I have as a group leader. It is difficult to prioritise different tasks when everything seems equally urgent and important, such as setting up the lab and new equipment, applying for grants, supporting my students and postdocs, preparing lectures, and writing papers. The feeling of never having quite enough time for all these different tasks can be tricky, particularly as I now am responsible not just for my own career, but also the career and success of my group members.

 

Carlo: Is there any advice you would give to young scientists at the beginning of their career?

Leonie: Everyone’s path in academia looks different and there is no single way that works for everybody. I think it’s really important to explore what aspects of research or academia you enjoy the most, how success looks like for you, and to figure out which path will allow you to pursue your goals. An important aspect of research as you progress in your career, at least in my opinion, is the ability to find research questions that you are excited about and that allow you to develop your own “niche”. You need to be able to show that your unique set of skills make you the right person to answer these questions. Besides that, support is essential at any stage. I am extremely lucky to have people that have supported and cheered me on, particularly in difficult moments. As exciting and exhilarating science is, it can also be challenging and frustrating at times and requires a lot of perseverance. For me, it has been crucial to have a strong network of friends, colleagues, and mentors who support me.

 

Carlo: Is there anything in particular that has helped you overcome difficult moments?

Leonie: Besides my family and friends, it was really helpful for me to realize that academia is only one of many possible paths in science. There are many different ways to define success and to be successful. Being a group leader in academia is just one of them.

 

Carlo: If you could change one thing about academia, what would that be?

Leonie: I think it is essential that we start allowing for more diverse career opportunities and paths within academia. Right now, with the current pyramid structure, very few people make it to “the top”, which is neither healthy nor sustainable. Changing this would have follow-on effects on many levels, allowing for more diversity and a more inclusive environment, which would in turn generate more creative ideas and approaches to solving the most pressing scientific challenges. This would benefit science as a whole and would help to limit rivalry and destructive competition and instead create a system that is based on collaboration and mutual support.

 

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About the Author

Carlo Pasini is a PhD student at ETH Zurich, and a 2024 Plantae Fellow. He studies the links between carbon metabolism and abiotic stresses, primarily focusing on guard cells. In his free time, Carlo enjoys reading, playing ice hockey and any kind of snow-related activity. You can find him on X: @Crl_Psn.