A trip down corn lane
By Román Ramos Báez
If you ask anyone what their favorite thing about summer is, their answer should of course be corn. This year, corn played an especially important role in my life. If you’ve ever looked closely at a cob of corn, you’ll notice that its kernels very satisfyingly line up into neat rows. Counting the rows, you’ll notice that the number is always even. These rows are specified in a series of steps by plant hormone signaling early in the development of the plant’s female inflorescence. The fact that a single plant hormone, auxin, is primarily responsible for orchestrating these processes makes the low frequency of errors in the placement of kernels that much more impressive. This summer, I spent most of my time working with Britney Moss running experiments and writing our manuscript focused on understanding the proteins that allow for the corn inflorescence to respond to auxin. In this process, I learned a lot about what it takes to write a story about your work, uncovered some of the secrets on the evolution of the maize (corn) auxin response, and left with a deeper appreciation for this amazing crop so carefully developed by indigenous scientists.
The plant hormone auxin plays a role in nearly every growth and developmental process not just in maize, but in all land plants. It does so through a group of receptor proteins, transcription factors, and repressors. These proteins are divided into families full of redundancy, and each of these protein families has dramatically expanded in numbers alongside the evolution of plant innovation, such as the development of leaves, flowers, seeds, etc. Together, they form a pathway that allows individual plant cells to respond to auxin inside them and depending on which family members are present in these cells, the same amounts of auxin will signal specialized cell differentiation. In Layman’s terms, this single hormone can tell different cells to develop into different organs depending on what auxin proteins are expressed in it. We believe the differences in the evolved functions of these proteins is what has resulted in the diversity of plant form that we see today.
In any given plant cell there are multiple members of the auxin circuit expressed at the same time, so the Nemhauser Lab has developed a model yeast system where the functions of these different proteins can be annotated in detail, characterizing single protein family members at a time. We can express members forming a minimal pathway and test circuits with different members to measure differences in how those proteins repress or activate auxin-responsive gene when auxin is added. In the past, this system has been used to characterize Arabidopsis thaliana auxin circuitry. To understand whether these functions are conserved across flowering plants, and specifically what these functions might be in maize, I recapitulated this same circuit with maize genes. Once my yeast lines were built, preliminary experiments showed these members to be functional in our yeast assays, I headed over to Walla Walla to work with Britney Moss at Whitman College.
My flight to Walla Walla took me close to Mt. Rainier, with breathtaking views of the Washington state landscape. I arrived at the airport alongside only 20 other passengers to find Brit ready to get me settled into her home. I purchased and ate my first Walla Walla sweet onion, went for a walk around the wheat fields surrounding the town, and we talked about our shared experiences being queer in academia. The rest was an intensive training on yeast cytometry experiments, followed by hours upon hours of drawing outlines, coding figure mock-ups, and writing sections of our manuscript. Because this was to be my first ever first-author paper, and Britney’s first time as the last author, we started off our manuscript plans with lots of ambition and optimism. It was only after getting back to UW that we realized we had scheduled too many experiments for ourselves to be able to finish our paper by the Fall. At first, we video chatted once a week, updating one another on our progress. Writing a paper with a collaborator in a different city can be challenging, but by the time the summer ended, email updates and texts had become a daily occurrence, and we found efficient ways to set and communicate our tasks and progress to each other. We finished our writing over a long weekend, when Brit came to visit us at UW, and we cranked out and reviewed the last bits together. I couldn’t have gotten through writing this paper without the help of all the maize collaborators in this grant that took the time to give us feedback, and without the incredible mentorship of Brit and Jennifer. If you’re interested in seeing our findings on maize auxin signaling, follow the link to our manuscript here: https://www.biorxiv.org/content/10.1101/844100v1.
Román Ramos Báez is a fourth year PhD student in Jennifer Nemhauser’s lab.
