Graduate Student University of North Carolina Carrboro, North Carolina
Body of Abstract: The phytohormone cytokinin regulates a variety of developmental processes, many of which are agronomically important, including seed yield, leaf senescence, and stress responses. Cytokinin has been directly linked to grain yield in rice (Oryza sativa), which makes the cytokinin signaling pathway a prime target for engineering more productive varieties. The major players of cytokinin signaling are conserved between rice and Arabidopsis, but the role of cytokinin in monocot growth and development has not been thoroughly defined. Here, we present an exhaustive phenotypic analysis of several higher and lower order null HK mutants in rice. We demonstrate that each HK gene has specific roles in development, such as shoot elongation, root elongation, and panicle architecture. While some roles are conserved between rice and Arabidopsis, there are multiple unique developmental effects of hk disruption in rice. Most notably, lines with loss-of-function mutations in all four HK cytokinin receptors (HK3, HK4, HK5, and HK6) display a shootless phenotype, whereas the corresponding triple null AHK mutant in Arabidopsis still produces a shoot, albeit a much smaller one. At least one copy of either HK5 or HK6 is necessary for shoot development and fertility. This work will contribute to our understanding of the unique roles of cytokinin in monocots and lay the foundation for developing rice varieties with agriculturally desirable traits.