I’m Claire Milsted, a PhD candidate in Plant and Microbial Biology (PMB). I study corn DNA repair and reproduction with Dr. Changbin Chen. I am also investigating a possible link between DNA repair and plant defense against diseases. This connection has been observed in another plant, Arabidopsis thaliana, but our understanding of it in corn is at an early stage.
My colleagues in the Chen lab work on a wide range of topics including plant cell biology, genetics, and plant breeding. Our main interest is meiosis, the special kind of cell division that leads to sperm and eggs in animals and pollen and megaspores in plants. Corn is a great plant for studying meiosis because it releases its pollen from a long tassel that can be easily dissected to investigate the stages of male meiosis that result in pollen.
Within meiosis, we are mostly interested in the “crossing over” process in which chromosomes exchange genetic material. The cell actually accomplishes this using its DNA repair machinery—the cell twists the DNA on purpose until a double strand break appears and is repaired. Some of the repairs are done in a crosswise fashion where one chromosome is used as a template to repair the other. Understanding this process in corn and finding possible patterns in where crossing over occurs would be a boon to plant breeders.
My thesis question is: how do the DNA repair genes RAD51 and BRCA2 affect reproduction, stress response, and defense against pathogens in corn? RAD51 and BRCA2 are ancient genes found in almost every organism with a nucleus, from microscopic algae to humans. In humans, loss of function mutations in RAD51 or BRCA2 lead to increased susceptibility to colon or breast cancers. These genes are also involved in the “crossing over” process in meiosis, which allows the creation of reproductive cells. When crossing over doesn’t work properly in plants, formation of pollen and megaspores is impaired. For example, some of my mutant plants’ anthers remain within the tassel and no pollen at all is released.
A lot of my work uses a reverse genetics approach, which means that I look at plants where genes of interest have mutated to be nonfunctional and I observe how that affects the plants. For me this entails growing a bunch of plants that might have a mutation, using PCR to figure out which of the plants actually have the mutation, and then comparing some specific trait between those with and without the mutation. One trait I am interested in is pollen viability, which I measure by staining the pollen with a special solution and observing it under a microscope.
However, since I can’t bring my microscope or other lab equipment into your homes, I’m going to focus on looking at seeds. In my research, I use seeds as one measure of reproductive success. For example, some of the mutant plants I am growing have very few corn kernels on each ear due to having lost function in rad51 or brca2 genes. Instead of looking at mutant corn, though, my activity this week will have you looking at seeds and fruit you can probably see around your neighborhood!
Here are some fun facts about plant reproduction from Claire:
Angiosperms, or flowering plants, represent 80% of all terrestrial plants! Most of our food, including fruit, grains, legumes, and most vegetables (some of which are botanically “fruits”) come from this group. However, they are relative newcomers, having only been around 130 million years. Dinosaurs, sharks, birds, and mammals are all older than flowering plants!
Some non-flowering plants you might see in your own backyard are more ancient, including moss (probably about 470 million years old), ferns (about 360 million years old), and conifers like hemlock and juniper (about 300 million years old).
Most of our favorite plants have perfect flowers with both male and female parts in each individual flower. Daylilies, roses, oak trees, and tomatoes are examples of this kind of reproductive system in plants.However, some plants are dioecious and have separate male and female individuals! Two native species with separate male and female plants that you may see around your neighborhood are juniper and jack in the pulpit. Red maples are often dioecious but some individual trees can have both male and female flowers on them.
Here is a fun bingo sheet you can do at home! Take a walk or hike a see what plant species you find along the way and identify them with this sheet!
If you want to learn more about native and non-native trees found on the U of M campus, visit www.campustrees.umn.edu
If you want to learn an incredible variety of info about almost every wildflower in Minnesota, head to https://www.minnesotawildflowers.info/If you want to watch an extremely goofy educational video that explains meiosis in animals in terms of a square dance, click here: https://www.youtube.com/watch?v=iCL6d0OwKt8
Header Photo by Nahil Naseer