UC San Diego

Plants possess the remarkable ability to continually generate new organs from undifferentiated tissue throughout many stages of their lives. For angiosperms, this includes their floral reproductive organs. Many different molecular signals coordinate the complex process of flower generation, but the foremost regulator is the phytohormone auxin. In this dissertation, we present work that has advanced our understanding of the flower initiation process and will provide useful methods and ideas for future research. In the introduction, we provide an overview of the main topics which this dissertation will address: genetic techniques in plant research, auxin signaling from a general perspective, and finally auxin transport and signaling as they relate to floral organogenesis. In Chapter 1, we detail an improved strategy for creating genetic materials for plant research. Specifically, we devised a technique to insert genetic sequences into desired genomic loci, also known as gene targeting. The new technology allows us to tag genes without relying on traditional random insertions into the genome. In Chapter 2, we present a genetic interaction between the auxin exporter PIN-FORMED 1 and the kinase PINOID. The results from this chapter indicate that flower formation depends on a stoichiometric balance between these two genes and that PIN- FORMED 1 is part of a larger protein complex that is yet to be characterized. In Chapter 3, we supply evidence that the three members of the ENHANCER OF SHOOT REGENERATION transcription factor family are required for flower initiation. We link the activity of these transcription factors to the auxin signaling pathway and identify a downstream target which is also a positive regulator of floral meristem formation. Finally, we conclude by discussing future directions for continuing the work presented in each chapter.