Kenyon College

HHMI Grants to Kenyon

Howard Hughes Medical Institute

Emily Vaughn '07 conducted summer research (poster) with
Dr. Luis Herrera Estrella, HHMI International Research Scholar
Other international fellows: Zhang, 2006; Tate, 2004

Emily Vaughn '07 at the Center for Investigation and Advanced Studies (CINVESTAV) in Irapuato, Mexico, where she worked with Dr. Luis Herrera-Estrella.

Emily at work in Herrera's laboratory, where she studied the effect of phosphatidic acid as a second messenger on expression of a phosphorus starvation gene in Arabidopsis thaliana.

Vaughn describes her research experience in Irapuato:

This summer I worked in the laboratory of Dr. Luis Herrera-Estrella in central Mexico, conducting research on phospholipid metabolism and signaling in the Arabidopsis thaliana primary root meristem. Dr. Herrera is one of about twenty principal investigators at the Center for Investigation and Advanced Studies (CINVESTAV) in Irapuato, Mexico. He is best known for his pioneering studies with Agrobacterium tumefaciens; in 1983 he became the first scientist to successfully transform a plant with Agrobacterium.

Irapuato is a small town halfway between Mexico City and Guadalajara that prides itself on being the world leader in strawberry production. Anyone born in Irapuato will refer to him- or herself as a “fresa,” or a strawberry (I had a much harder time explaining why, because I’m from North Carolina, I am known as a “Tar Heel.”). Due to the city’s high elevation (over a mile above sealevel), the weather was much less severe than one might expect. Still, I took every opportunity I had to linger in the 0°C storage room!

In the lab, I worked directly under Alfredo Cruz-Ramirez, the lab’s postdoc, who loves the Beatles, Led Zeppelin, and classic rock in general; in other words, he made me feel right at home. I spent my first weekend in Mexico at Alfredo’s parents’ ranch in the state of Hidalgo eating pig-hand meat tacos, picking garambullos (cactus berries) for a midday snack, and sharing chili and cherry-flavored gum with Alfredo’s three year-old son.

I typically spent about ten hours every weekday in the lab, and traveled with friends from the lab on weekends. I managed to be in San Miguel de Allende for La Fiesta de los Locos, or the Festival of the Crazies. The fiesta is centered around a 3 hour parade where hundreds of people march through the city in incredibly elaborate homemade costumes and throw candy (again, usually chili-flavored) to people watching on the sidewalk. It’s like a Mexican mardi gras. Some of the costumes must have taken hours to make, and some groups had two dozen people coordinated to look like Aztec warriors, with such attention to detail that they all had the same color of facepaint to make their legs look dirty. And wow, was the music loud.

Vaughn with coworkers at CINVESTAV

Traditional Aztec dancers in the Zócalo, Mexico City.

Another weekend, Emmanuel, a master’s degree student in the lab, and I visited Mexico City and stayed with his family. In the Bellas Artes center, we saw Diego Rivera’s second version of the contraversial mural that was torn down in Rockefeller Center. I also enjoyed visiting a street fair of Oaxacan crafts and foostuffs. My favorite part of the fair was the man who twirled pink cotton candy into the shape of sombreros. The next day, Emmanuel and I went to Teotihuacan, a 2000 year-old holy city and archeological hot-spot, and climbed to the top of the pyramids of the Sun and Moon.

Arabidopsis thaliana is one of the most commonly studied model organisms in plant biology because it is small, fast-growing, and its entire genome has been sequenced. By studying Arabidopsis, scientists can more easily, cheaply, and quickly obtain data that can usually be extrapolated to other plants of interest. Although this was my first time working in a research lab, I had some prior familiarity with Arabidopsis from my introductory lab courses, and from preparing to study floral induction regulation in Dr. Karen Hicks’s lab at Kenyon this fall. I look forward to comparing the techniques I learned in Mexico with those used in the Hicks lab.

The principal focus of the Herrera lab is phosphorous starvation in Arabidopsis thaliana. The lab has identified plants with mutations in their internal or external phosphorus detection systems and uses the mutants to study the physiological mechanisms by which plants obtain sufficient phosphorus when the element is scarce. Observed responses in Arabidopsis include lengthening of root hairs, greater lateral root density, and changes in the root meristem. The primary goal of the laboratory’s research is to determine how plants acquire phosphorus and use it efficiently, to the end of facilitating the development of plants that can withstand phosphorous-poor soil.

People in the lab--master’s degree students, PhD students, and summer students-- approach that topic from different angles, such as interplay with auxins, characterizing P-deprivation-tolerant mutants, and metabolic pathways. I focused on the latter. Alfredo had designed a branch-out project for me to conduct, to see if phospholipid signaling could be related back to P-starvation, specifically through phosphatidic acid (PA). PA is a known second messenger, and its concentration decreases in phosphorous-starvation conditions, whereas the abundance of other lipids increases. We hypothesized that phospholipids are broken down to PA under P-starvation to make available its phosphorus for metabolic processes.

This figure shows an example of the data we collected, showing representative root meristems for each concentration. Note how expression of GUS (blue) decreases with greater concentrations of the treatment, and how the organization of tissue lines is lost at 10uM treatment; yet GUS expression and tissue organization remain constant in the negative control as compared to the general control.

Our project was composed of several tests that blocked or up-regulated the two different phospholipase pathways that produce phosphatidic acid and then examined 1.) what adaptive responses occur in the root meristem as a result of changes in PA biosynthesis, specifically in the quiescent center (QC), and 2.) whether the PA that functions as a secondary messenger to the QC is primarily derived from the phospholipase C (PLC) or the phospholipase D (PLD) pathway.

The quiescent center is a group of four to seven mitotically inactive cells in the root primary meristem that confer identity to neighboring cells which then differentiate into different lines of tissue. Evidence for changes in the QC, or in the meristem in general, was gathered by observing changes in GUS staining and cell organization patterns in certain transgenic promoter-trap lines of Arabidopsis. The primary root meristem has a very regular pattern, and under high magnification, it was clear to us when a treatment had an effect upon meristemal cell identity because the tissue lines became disorganized. Likewise, the marker lines we used specifically expressed GUS in the QC, in the case of pQC46:GUS, or distally concentrated GUS in the case of pPLT1-1:GUS. Still, since the data was qualitative, we often gathered data blindly, judging whether or not we observed changes in GUS expression or organization without knowing what treatment or concentration we were seeing.

In addition to developing my skills as a researcher, working in Irapuato gave me the opportunity to practice my language skills. Although they have many collaborators in the United States, and the language of publication is almost exclusively English, on a daily basis people in the lab spoke to one another in Spanish. It was interesting to me how most of the researchers could easily read an article in English, but few could speak English conversationally. By the end of my ten-week stay, I was thinking in Spanish more than English: not just in the lab, but on lunch breaks, and when I spent time with people after work. It was even difficult for me to speak to my parents on the phone because I first had to translate my thoughts into English.

I am grateful to everyone in the lab for their guidance and friendship. CINVESTAV’s Irapauato unit is one of the leading plant research centers in Mexico, and I feel very fortunate to have had the chance to study under such great tutorage. It was a wonderful opportunity to see the ways in which science crosses international boundaries. For example, when I went to see a cheesy American sci-fi movie with a friend from the lab and her fiancee, we were all able to laugh together when the “scientist” character looked at another character with an X-ray and said “We need to isolate your recombinant DNA.” All jokes aside, I look forward to continue working to strengthen the international scientific community, and I thank the Howard Hughes Medical Institute and Kenyon for giving me this opportunity to begin to do so.