Analysis of the maize cytokinin receptor Zea mays Histidine Kinase 1 function using Saccharomyces cerevisiae

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Rogers, Anna
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Symposium on Undergraduate Research and Creative Expression
Iowa State University Conferences and Symposia

The Symposium provides undergraduates from all academic disciplines with an opportunity to share their research with the university community and other guests through conference-style oral presentations. The Symposium represents part of a larger effort of Iowa State University to enhance, support, and celebrate undergraduate research activity.

Though coordinated by the University Honors Program, all undergraduate students are eligible and encouraged to participate in the Symposium. Undergraduates conducting research but not yet ready to present their work are encouraged to attend the Symposium to learn about the presentation process and students not currently involved in research are encouraged to attend the Symposium to learn about the broad range of undergraduate research activities that are taking place at ISU.

The first Symposium was held in April 2007. The 39 students who presented research and their mentors collectively represented all of ISU's Colleges: Agriculture and Life Sciences, Business, Design, Engineering, Human Sciences, Liberal Arts and Sciences, Veterinary Medicine, and the Graduate College. The event has grown to regularly include more than 100 students presenting on topics that span the broad range of disciplines studied at ISU.

Genetics, Development and Cell Biology

Cytokinins (CK) regulate a diverse assortment of processes in plants, including cellular division, biosynthesis of chloroplasts, and differentiation within root and apical meristems. Response to CK is regulated through a two-component signal transduction system consisting of a receptor and a response regulator. Two-component signaling systems are highly conserved in bacteria, fungi and plants and allow organisms to sense and respond to external and internal stimuli. Our analysis of the semi-dominant, leaf patterning maize mutant Hairy Sheath Frayed1 (Hsf1) identified the maize CK receptor Zea mays Histidine Kinase1 (ZmHK1) as the underlying gene. The Hsf1 phenotype is marked by the outgrowth of proximal leaf tissue (sheath, auricle and ligule) in the distal leaf blade, reduced leaf size, and increased leaf pubescence. Missense mutations in the CK binding domain of ZmHK1 increase ligand binding affinity, resulting in CK hypersignaling and giving rise to altered leaf patterning in Hsf1. We are using a two-component signaling assay in Saccharomyces cerevisiae to understand the relationship between these amino acid changes and altered ZmHK1 activity. We have assayed the three independent Hsf1 alleles (Hsf1-1595, Hsf1-1603, and Hsf1-AEWL) using the yeast system and found some signal in the absence of added CK. We are making additional targeted amino acid changes near the CK binding domain in ZmHK1 to determine which residues are critical for ligand recognition, binding and signaling. Our current results will be presented.

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