Marley Shouldice: Studying Plant Defense Mechanisms

My name is Marley Shouldice and I am a very grateful recipient of the IDEA Grant during the Summer 2022 semester. My research focuses on fungi known as Dark Septate Endophytes. Unlike mycorrhizae, another type of fungi which many gardeners/backyard scientists may be familiar with, the ecology of Dark Septate Endophytes (abbreviated DSEs) is poorly understood. This is unfortunate considering that they are very widespread and can colonize many crop plants. With my research, I hope to uncover how these mysterious organisms interact with plants.

Marley Shouldice, Junior, Biological Sciences

Specifically, I am investigating how DSEs change the way plants defend themselves against insects. That’s right- plants have chemical mechanisms to protect themselves against insect damage, similar to the way our own immune systems protect us from disease! Not only do plants always have a baseline response to damage, known as constitutive defense, but they also can prepare a more intense and specialized response when they expect more damage, just like how our bodies can recognize the same disease a second time and fight it even more strongly. I am also interested in examining how drought conditions influence these defenses, given that DSEs are hypothesized to support plant growth in harsh climates and drought.

To study DSEs, I first had to find one and actually grow it. While I’d had experience growing shiitake or oyster mushrooms on sawdust, these fungi were confusing considering that they only live underground, inside plant roots. I had no idea how I would even identify a DSE, let alone sample it and culture it! Fortunately, my mentor, Dr. Nora Underwood, knew someone who could help. She introduced me to her friend Dr. Jennifer Rudgers, an ecologist studying Dark Septate Endophytes at the University of New Mexico. Dr. Rudgers gave me amazing guidance on finding current literature and on her laboratory methods of culturing DSE from field samples. With the help of the generous IDEA Grant Donors as well as the Rudgers Lab, I was given the amazing opportunity to travel to Dr. Rudgers’ lab in New Mexico to learn about culturing DSEs.

A view from the plane in New Mexico.

In early May this summer, I packed my bags and hopped on the plane to New Mexico. I had never been to such a dry place before; it looked as though I had landed on another planet when I arrived! I was soon greeted by one of Dr. Rudgers’ knowledgeable lab technicians. She gave me a tour of UNM as well as the lab. Over the next few days, she taught me how to culture fungi from roots and leaves, how to stain and identify DSEs under a microscope, how to pour agar into petri dishes (which will provide food and a substrate for the fungi), and how to work under a biosafety hood to minimize contamination. Not only did she teach me in detail all of the procedures I would need for my research, but she also fielded my seemingly infinite questions. I also met with Dr. Rudgers herself, who personally reviewed my research plans and gave me wonderful feedback. She offered me some cultures that had already been genetically identified, which would save me substantial time in trying to figure out what species I’d cultured. Soon, I felt very confident with the subject and was excited to get to work with all that I had learned and my new cultures. I am immensely grateful to Dr. Rudgers, her amazing lab technicians, and her graduate students who were so kind in giving me everything I needed to delve head-first into the subject.

Isolating fungi from plant roots at the Rudgers Lab.

When I returned, I began preparing for my own experiment. I decided to use corn as the plant, considering that the DSEs I’d been given were isolated from a grass species, and corn is in the grass family (Poaceae). Using Dr. Rudgers’ protocol, I poured my own agar media into petri dishes and inoculated them with fungi (from the UNM cultures). I also sterilized corn seeds (using Dr. Rudgers’ protocol) and placed them inside the petri dishes with the fungi. I used three different DSE species, Fusarium oxysporum, Periconia macrospinosa, and a species in the order Sordariales.  I also inoculated corn with sterile agar media for a control (in case the media itself were to have any effect).

My setup for pouring petri dishes.

It worked! Corn and fungi are growing just two days later.

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