Trevor Nolan's favorite plant is one that glows in the dark. Though Arabidopsis thaliana is not naturally fluorescent, in the lab, it is an extensively researched model organism that can be genetically modified to label its cells with fluorescent proteins under various conditions, enabling precise imaging. This allows developmental biologists like Nolan to answer fundamental questions about how plants grow at the cellular level.
More specifically, Nolan focuses on how cells that make up a plant's roots send signals to one another and adapt to their environments. After completing his PhD at Iowa State University and a postdoctoral fellowship at Duke University, Nolan joined the Caltech faculty as an assistant professor of biology and biological engineering this year. We spoke with him about his research into the mechanisms underlying plant development, and the inevitable struggles of keeping houseplants happy.
You study how plants behave when they're "stressed." What does it mean for a plant to be stressed?
Plants face all kinds of stress. They can't move to escape it. Too much or too little water, salinity, nutrient stresses. You name it, plants have had to face it. So, they have developed sophisticated signaling mechanisms and a remarkable ability to adapt their bodies to suit their environment, changing in response to light, gravity, water availability, and other variables. This is critically important in the face of climate change, as we start to think about how we want to engineer plants to grow and develop optimally without having detrimental side effects. For example, plants can be engineered to be drought tolerant, but they often also end up growing less. We're interested in understanding how to change a plant precisely when and where it's needed to mitigate those trade-offs.
An important part of understanding the "wiring diagrams" of plants is figuring out how cells signal to each other. Our long-term goal is to understand the systems that control plant development sufficiently so we can start to rewire them. We want to be able to tune them for specific conditions. For example, in a drought, you might want roots to grow longer in order to access water in the soil better. To do this, we first need a mechanistic and comprehensive understanding of how plant development works, not just in individual cells but in the whole context of the organism.
Why does your work focus specifically on roots?
Roots are an excellent system to study because they contain a complete developmental timeline. Within half a centimeter of the root, you can trace from the stem cell to fully mature tissue for about a dozen cell types. Each cell has to do a different job. We're curious how cells adopt distinct functions but also work together for a whole organism to grow and develop. A central question we are asking is how the cells transition from dividing to differentiating and how that is coordinated across different cell layers of a growing organism. You can watch development happen in real-time and see what happens if you make a change to one cell, exploring questions like: What happens to the next cell over? How are these responses being coordinated in order for the whole organ to grow and develop?
We primarily focus on Arabidopsis, which is sort of the "lab rat" of the plant world.
What are the different jobs a root cell can have?
There are about a dozen different cell types within the root. You have, for example, vascular cells in the center of the root that transport water or nutrients over long distances. There are also the root hair cells in the outer epidermis that provide increased surface area to take up water and nutrients from the environment. Other cells on the root's interior are involved in forming barriers to dictate what's getting in or staying out of the root. There's beautiful literature that has described the specific genetic markers for the various cell types. Combined with modern techniques like single-cell and spatial genomics that give you a detailed picture of the gene expression inside individual cells, we've started to be able to understand what's happening in each of those different cells and what their behavior looks like in space and time. We can look at different contexts, like what happens when the plant is stressed or responding to a specific hormone. For example, we recently discovered that a particular cell type, the cortex, responds to a hormone called brassinosteroids at a specific stage of its development, which is important in determining how much a root grows.
What got you interested in studying plants?
A fascination for genetics. I was a student in genetics and was taken by the way that we can understand how biology works by doing things like genetic manipulations. Plant biology has played an essential role in our understanding of genetics all the way back to people like Gregor Mendel [19th century biologist and pioneer in the field of genetics]. I started working in a plant biology lab and was hooked by the experiments that we can do in plants relatively quickly and easily that may be challenging or more onerous in some other systems.
My fascination revolves around the desire to understand how life generally works. What are the fundamental principles of how biology operates, how genetic systems work? I love the ability to incorporate cutting-edge approaches that let us watch things happen in real time, where we can see what's going on, when, and where it's happening. Plants have this amazing array of sizes and shapes, both at the cellular level and at the organ level, that I find captivating, and it's encouraging to see increased interest in plant biology and sustainability in these kinds of areas.
What excites you most about your work?
I love looking at Arabidopsis when it's expressing many different fluorescent proteins in different places within its cells. Just seeing cells glowing with different signals and revealing the biology that's happening within, there's not much that's more exciting.
In our lab, we're building a custom microscope system that will allow us to image plants as their roots grow toward gravity. It's kind of like a normal microscope that's been flipped 90 degrees to image the plant from the side, instead of above, as the roots extend downward. We'll be able to perform live imaging of cellular dynamics with many different fluorescent colors. We want to watch from when a stem cell first divides to when the cell is fully mature, and we want to do this not just for one cell type, but for neighboring cell types, so that we can understand the coordination of growth.
Being at a place like Caltech gives us the flexibility and resources to make this kind of system a reality. There are a few of them in Europe, but this will be the first one in North America. By integrating this ability to watch developmental dynamics in a growing organ with technologies like single-cell and spatial genomics, we'll reveal the genes that turn on or off in different cells and how their expression programs relate to cellular decisions. We can then use this knowledge and genome engineering tools to reprogram how plants grow.
How does your work fit in and collaborate with other labs at Caltech?
One of Caltech's most remarkable aspects is its collaborative atmosphere, which fosters synergies across diverse fields. Our research has significantly benefited from these interactions, particularly in development, genomics, and environmental interactions, including plant–microbe relationships. Much of the foundational work that established Arabidopsis as a model organism was conducted in the lab of Elliot Meyerowitz [George W. Beadle Professor of Biology, Howard Hughes Medical Institute Investigator] here at Caltech. Although our research focuses on opposite ends of the plant, we share many common interests in stem cells and developmental biology and have recently recruited a joint postdoc to further the interactions between our groups.
Caltech also hosts an exceptional community of researchers focused on microbes, catalyzed by initiatives such as the Center for Environmental Microbial Interactions (CEMI). These interactions are particularly relevant for understanding plant growth in natural, nonsterile environments. For instance, we are collaborating with Gözde Demirer [Clare Boothe Luce Assistant Professor of Chemical Engineering] from the Division of Chemistry and Chemical Engineering to explore how beneficial microbes can be harnessed to support plant growth under challenging environmental conditions and promote sustainability. Our research aligns closely with the goals of the Resnick Sustainability Institute and will be enabled by the advanced facilities available at the new Resnick Ecology and Biosphere Engineering Facility.
Additionally, Caltech provides remarkable opportunities in genomic technologies, with several collaborations driving innovation in this space. We are working with the lab of Mitchell Guttman [professor of biology] to develop novel single-cell approaches that could enable us to profile many more cells and samples. We have also greatly benefited from interactions with labs involved in the Cell Interactome Initiative (CI2), including Barbara Wold [Bren Professor of Molecular Biology; Merkin Institute Professor], Long Cai [professor of biology and biological engineering], Matt Thomson [professor of computational biology, Heritage Medical Research Institute Investigator], Michael Elowitz [Roscoe Gilkey Dickinson Professor of Biology and Bioengineering, Howard Hughes Medical Institute Investigator], Lior Pachter [Bren Professor of Computational Biology and Computing and Mathematical Sciences], and Kai Zinn [Howard and Gwen Laurie Smits Professor of Biology]. This initiative aims to understand how cells develop and interact within tissues using cutting-edge technologies such as spatial omics. These are just a few examples; there are too many more to list. It's incredible what a stimulating and collegial scientific environment that Caltech provides.
What do you like to do when you're not looking at roots?
I spend a lot of my time raising and playing with my three kids, often biking around Pasadena with my kids on the back. And I'm into weightlifting and fitness. I also dabble in night-sky photography, so I think California's going be fantastic for that. There are so many places where you can see the Milky Way away from the lights in LA.
Do you have any advice for people who can't seem to keep their houseplants alive?
Water them, but not too much. I've been known to kill some houseplants too. It happens to all of us.
Trevor Nolan
Credit: Caltech
