Trevor Nolan’s preferred plant is one that illuminates in the dark. While Arabidopsis thaliana is not inherently fluorescent, it is a extensively studied model organism that can be genetically overhauled in the laboratory to tag its cells with fluorescent proteins under diverse conditions, facilitating precise imaging. This capability enables developmental biologists like Nolan to tackle essential inquiries regarding how plants grow at the cellular scale.
More specifically, Nolan concentrates on how cells constituting a plant’s roots communicate signals to each other and adjust to their surroundings. After obtaining his PhD at Iowa State University and completing a postdoctoral fellowship at Duke University, Nolan became a member of the Caltech faculty as an assistant professor of biology and biological engineering this year. We conversed with him about his investigation into the processes behind plant development and the unavoidable challenges of keeping houseplants thriving.
You investigate how plants react when they’re “stressed.” What does it signify for a plant to be stressed?
Plants encounter various forms of stress. They lack the capacity to escape it. Excessive or insufficient water, salinity, nutrient deficiencies—plants have to confront it all. Therefore, they have evolved intricate signaling pathways and an impressive capacity to adjust their physiology according to their surroundings, modifying in reaction to light, gravity, water availability, and additional factors. This understanding is vitally crucial amid climate change, prompting us to consider how we can engineer plants to thrive and develop optimally without adverse side effects. For instance, while it is possible to engineer plants for drought resistance, they often result in reduced growth. Our objective is to comprehend how to modify a plant precisely when and where required to alleviate those trade-offs.
A vital aspect of deciphering the “wiring diagrams” of plants is uncovering how cells communicate with one another. Our long-term aspiration is to grasp the systems that govern plant development adequately so that we can begin to rewire them. We aim to tune them for specific scenarios. For instance, during a drought, it may be beneficial for roots to elongate to enhance water access in the soil. Achieving this requires a mechanistic and holistic comprehension of plant development, not just at the level of individual cells, but in the wider context of the entire organism.
Why does your research concentrate specifically on roots?
Roots represent an excellent model for investigation as they encompass a complete developmental timeline. Within a half-centimeter slice of the root, one can observe the progression from stem cells to fully matured tissues across around a dozen distinct cell types. Each cell performs a unique role. We are intrigued by how cells acquire specialized functions while simultaneously cooperating for the growth and development of the whole organism. A pivotal inquiry we are exploring is how cells transition from division to differentiation and how this process is synchronized across various cell layers of a developing organism. Observing development in real-time allows us to see the effects of altering one cell, probing questions such as: What occurs in the adjacent cell? How are these reactions coordinated for the entire organ’s growth and development?
Our primary focus is on Arabidopsis, which is often regarded as the “lab rat” of the botanical realm.
What diverse roles can a root cell perform?
There are approximately a dozen distinct cell types present within the root. For instance, vascular cells situated at the center of the root transport water and nutrients over substantial distances. Additionally, root hair cells located in the outer epidermis contribute to increased surface area for absorbing water and nutrients from the environment. Other cells within the root’s interior are instrumental in establishing barriers that determine what enters or exits the root. There exists rich literature that outlines specific genetic markers for the various cell types. When combined with modern techniques such as single-cell and spatial genomics, which provide an intricate view of gene expression within individual cells, we have begun to discern the activities taking place in each of those distinct cells and how their behavior evolves over time and space. We can examine various contexts, like the responses of the plant when under stress or reacting to particular hormones. For instance, we recently identified that a certain cell type, the cortex, reacts to a hormone known as brassinosteroids at a specific developmental stage, which is crucial in determining root growth capacity.
What sparked your interest in studying plants?
A deep interest in genetics. I was a student of genetics, fascinated by the manner in which we can comprehend biological processes through genetic manipulation. Plant biology has been pivotal in advancing our understanding of genetics, tracing back to early figures like Gregor Mendel [19th century biologist and genetics pioneer]. I began working in a plant biology lab and was captivated by the speed and simplicity with which experiments could be conducted on plants, which might be more complex or labor-intensive in other research systems.
My intrigue is largely fueled by the desire to unravel the workings of life itself. What are the fundamental principles governing biological functions, and how do genetic systems operate? I relish the capacity to utilize cutting-edge methodologies that allow us to observe processes in real time, enabling us to pinpoint what is happening, when, and where. Plants exhibit a remarkable diversity of sizes and shapes at both the cellular level and the organ level, which I find fascinating, and it is uplifting to witness a growing interest in plant biology and sustainability in these areas.
What excites you the most about your research?
I find immense joy in observing Arabidopsis expressing various fluorescent proteins in different locations within its cells. The sight of cells emitting different signals and unveiling the underlying biological processes is genuinely exhilarating.
In our laboratory, we are developing a specialized microscopy system designed to visualize plants as their roots grow in response to gravity. This system resembles a conventional microscope that has been rotated 90 degrees, allowing us to capture images of the plant from the side as its roots extend downward. We will be able to conduct live imaging of cellular dynamics employing many diverse fluorescent colors. Our aim is to observe the process from the initial division of a stem cell to the maturation of the cell, not only for one cell type but also for adjacent cell types, enabling us to comprehend the coordination involved in growth.
Being part of an institution like Caltech provides us with the flexibility and resources necessary to transform this vision into reality. Although a few similar systems exist in Europe, this will mark the first implementation in North America. By merging our capability to observe developmental dynamics in a growing organ with technologies such as single-cell and spatial genomics, we will uncover which genes activate or deactivate in different cells and how their expression programs influence cellular decisions. We aim to employ this knowledge and genetic engineering tools to reprogram plant growth mechanisms.
How does your work integrate with and collaborate with other laboratories at Caltech?
One of the most extraordinary features of Caltech is its cooperative environment,
which promotes collaborative efforts across varied domains. Our studies have greatly profited from these collaborations, especially in areas such as development, genomics, and environmental dynamics, including plant–microbe interactions. A significant portion of the pioneering research that positioned Arabidopsis as a key model organism was carried out in the laboratory of Elliot Meyerowitz [George W. Beadle Professor of Biology, Howard Hughes Medical Institute Investigator] here at Caltech. Despite our research concentrating on different aspects of the plant, we possess several overlapping interests in stem cell research and developmental biology, and we have recently appointed a joint postdoc to enhance the collaboration between our teams.
Caltech also features an outstanding network of researchers dedicated to microbial studies, spurred by projects such as the Center for Environmental Microbial Interactions (CEMI). These collaborations are especially pertinent for comprehending plant development in natural, non-sterile ecosystems. For example, we are partnering with Gözde Demirer [Clare Boothe Luce Assistant Professor of Chemical Engineering] from the Division of Chemistry and Chemical Engineering to investigate how beneficial microbes can be utilized to enhance plant growth in adverse environmental circumstances and advance sustainability. Our investigations closely align with the objectives of the Resnick Sustainability Institute and will be supported by the cutting-edge facilities at the newly established Resnick Ecology and Biosphere Engineering Facility.
Furthermore, Caltech offers exceptional prospects in genomic technology, with numerous partnerships fostering innovation in this domain. We are collaborating with the lab of Mitchell Guttman [professor of biology] to create innovative single-cell methods that may allow us to analyze a significantly larger quantity of cells and samples. Additionally, we have greatly benefited from interactions with laboratories engaged 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 strives to comprehend how cells function and interact within tissues by leveraging advanced technologies such as spatial omics. These are merely a few instances; many more exist. It’s remarkable the vibrant and collaborative scientific atmosphere that Caltech fosters.
What do you enjoy doing when you’re not observing roots?
I dedicate a considerable amount of my time to nurturing and engaging with my three children, often cycling around Pasadena with them in tow. I’m also passionate about weightlifting and fitness. I have a pastime in astrophotography as well, so I believe California will be wonderful for that. There are countless locations where one can view the Milky Way away from the urban glare of LA.
Do you have any tips for individuals struggling to keep their houseplants thriving?
Water them adequately, but be cautious not to overdo it. I’m guilty of losing some houseplants as well. It’s a common occurrence for all of us.