FUNCTIONAL CHARACTERIZATION OF ZEA MAYS EARLY HEADING DAY 1 AND DEVELOPMENT OF CRISPR-CAS9 FLOWERING TIME EDIT ANALYSIS STRATEGIES FOR MAIZE IMPROVEMENT

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2024

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With the human population increasing, it is essential to find novel ways to increase sustainable food production. Maize is a globally important staple, but due to differences in flowering time, we are not able to fully utilize the extensive genetic diversity for crop improvement. Tropical maize has the potential to contribute desirable traits such as pest/disease resistance, stalk stability, and drought tolerance to temperate breeding efforts, but its late flowering in temperate environments limits its use. Understanding the molecular genetic network controlling maize flowering time allows for the use of plant biotechnology strategies to address this issue. My project aims to (i) functionally elucidate the molecular mechanisms of the maize flowering time promoter Zea mays Early heading date 1 (ZmEhd1), and (ii) establish a protocol for analyzing transgenic maize with targeted edits in flowering time repressors. ZmEhd1 is a homolog of the rice Ehd1 flowering activator and encodes a B-type response regulator, like transcriptional activators of the cytokinin signaling pathway. I am using a maize protoplast system to determine if ZmEhd1 localizes to the nucleus and create deletions to map the ZmEhd1 nuclear localization domain. There are three known major flowering time repressors including ZmCCT9, ZmCCT10 and ZmRap2.7. We have taken the approach to knock out the function of these repressors using a CRISPR Cas9 system. My role involves analyzing these transgenic plants through different methods including, Tracking of Indels by Decomposition (TIDE) and subcloning analysis. Understanding the functional determinants of ZmEhd1 provides a more complete picture of its role in the maize flowering time network. Additionally, establishing a protocol for transgenic analysis at the University of Hawai‘i at Mānoa is necessary to continue using these novel biotechnological approaches to amend the flowering issues in tropical maize. This work will allow broader use for tropical maize in breeding programs worldwide, thus helping to improve sustainable food production.

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Molecular biology, Genetics, CRISPR Cas9, Flowering time, Nuclear localization, Tropical maize, ZmEhd1

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64 pages

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