PhD Exit Seminar
Advisor: Dr. Kristin Mercer
Committee: Dr. Erich Grotewold, Dr. Leah McHale and Dr. Andy Michel
Maize and Sunflower of North America: Conservation and Utilization of Genetic Diversity
The genetic diversity in the crop landraces and crop wild relatives (CWRs) of the world is the ‘biological cornerstone’ of food security. Two steps that could intensify its in-situ conservation are: 1) determining how natural selection has shaped the distribution of functional genetic diversity across the landscape; and 2) identifying potential threats to this diversity. In this body of work I provide examples of both.
First, I sought understanding of how natural selection has shaped functional genetic diversity in Zea mays (maize) landraces grown along an elevational cline in Chiapas, Mexico by using RNA-seq approaches. We collected maize landraces from three distinct elevations (highland, ~2100 m; midland, ~1550 m; and lowland, ~600 m) and planted them in a midland common garden. RNA-seq was performed on young leaf tissue. Weighted gene co-expression network analysis was used to identify co-expressed gene modules among landraces. Association analysis was then performed between landrace module expression values and environmental parameters of landrace origin. We identified an apparent trade-off between an ABA dependent abiotic stress response in the lowland landraces and a possible plasma membrane repair response in the highland landraces. We then used the RNA-seq dataset to find signals of genetic differentiation in phenylpropanoid, flavonoid, and lignin biosynthesis between highland and lowland maize landraces. Highland landraces showed increased expression of genes involved in flavonol biosynthesis and a gene at the entry point into hydroxycinnamate biosynthesis. Alternatively, lowland landraces showed increased expression of genes involved in anthocyanin and lignin biosynthesis.
Second, I studied how the processes of natural selection influenced the introgression of crop-like traits into wild Helianthus annuus (sunflower) populations, which can lead to loss of genetic diversity in wild populations. Four crop-wild hybrid cross types, commonly found in sunflower hybrid zones, were grown together in a hybrid zone setting. We compared growth and life history traits and performed phenotypic selection analysis on early season traits to ascertain the likelihood, and potential routes, of crop allele introgression into wild sunflower populations. The four cross types overwintered, emerged in the spring, and survived until flowering, indicating no early life history barriers to crop allele introgression. Direct selection for increased early season leaf size led to indirect selection on both increased early season plant height and earlier emergence. We identified variation in selection intensities given cross type, which has implications on routes of crop allele introgression.
Combined, we provide examples of: 1) how functional genetic diversity is spread across the landscape; and 2) how crop toward wild introgression proceeds.
Friday July 25th, 2014
8:30 AM – 9:30 AM
102 Rightmire Hall (Columbus)