Maize pyruvate orthophophate dikinase (PPDK), its role in C4 photosynthesis, and the tissue specific expression of PPDK throughout various tissues of maize and in the developing maize kernel.
C4 photosynthetic plants (such as maize) evolved from ancestral C3 plant species due to environmental changes that resulted in a decrease in CO2 availability and a need to use CO2 more efficiently. Pyruvate orthophosphate dikinase (PPDK) located in the chloroplasts of mesophyll cells plays a pivotal part in C4 photosynthesis and its role is to catalyze the regeneration of PEP, the initial CO2 acceptor molecule in C4 photosynthesis. Two PPDK isoforms are encoded on chromosome 6 by a dual promoter system – one encoding the cytosolic C3 isoform and one encoding the chloroplastic C4 isoform. The goal of this research project was to test tissue specific expression of C3 and C4 isoforms of PPDK in various tissues of maize (leaf, sheath, root) at different treatments (high light, low light, dark grown, greening) along with expression in the developing maize kernel. RNA was isolated from the samples and quantitative polymerase chain reaction (QPCR) was subsequently run to test for expression of each isoform. In the high light vs. low light treatments, both isoforms were expressed similarly with highest expression in more photosynthetic tissues (leaf portions). In greening trials, sheath PPDK expression was seen to have more of a response to light than leaf tip PPDK. Kernel expression was primarily C3 PPDK dominated with a peak expression at 12 days after pollination. The more we learn about PPDK and C4 photosynthesis, the closer we can become to introducing C4 traits to C3 plants, increasing photosynthetic capability, yield, and production.
What I gain most from my REU experience at BTI was a learning experience unmatched to anything I have ever received from a lecture, seminar, or lab class before this. As an intern, I was introduced to a topic I knew very little about, expected to learn the topic front to back, and be able to write about and communicate the main points to others. Working with my mentor (Pinghua Li of the Brutnell Lab) was very beneficial – she was willing and happy to teach me lab skills, help me to understand the reasons behind what I was doing, and as her confidence and trust in me grew, I was able to work independently on my project while still inquiring her for help if needed. My attention to detail skyrocketed, my lab skills were honed, writing and verbal communication improved, and I developed a deeper appreciation of the hard work and time that goes into true research. These are the reasons that made this summer memorable and as I am applying for graduate school in the fall, I can look back at my work and use it as a reference for what I will again be doing as I work toward my future degree. The skills I learned, the friends I made, and the experiences I had made this whole summer worthwhile.