Floral Meristem Termination in Aquilegia

Abstract

The persistent activity of stem cells in meristems is the foundation of continuous growth in plants. During the reproductive phase, vegetative meristems that produce leaves will be converted into floral meristems (FMs) to produce flowers. Unlike the vegetative meristems, which can generate new leaves continuously throughout the lifespan of a plant, the stem cell activity in a FM will always terminate at a specific time point, since each flower only has a finite number of organs. Floral meristem termination (FMT) is, therefore, one of the defining features of FM identity and variation in the timing of FMT is an essential source of generating floral morphological diversity. However, how this process is fine-tuned at a developmental and evolutionary level is still poorly understood. In this dissertation, I have sought to lay the groundwork for understanding how FMT is regulated in Aquilegia and thereby promote Aquilegia as a model system for studying FM regulation. In Chapter 1, I conducted in-depth transcriptome sequencing of finely dissected developmental stages of the FM of A. coerulea, covering the developmental window before and after FMT, and identified key genes that function as hub loci in major genetic modules or mark the transitions between key developmental stages. In Chapter 2, I analyzed how the dynamic between cell proliferation and cell expansion changes during primordia initiation and FMT using a newly developed quantitative live-confocal imaging method. This was the first live-imaging application for FMs that produce more than four whorls of floral organs with an apocarpous gynoecium and was the first investigation of cell behavioral dynamics during the FMT developmental window in any plant. In Chapter 3, I used stamen whorl number as a quantitative trait to represent the timing of FMT and conducted QTL mapping in the F2 progeny of a cross between two sister species, A. brevistyla and A. canadensis. I discovered that the genetic architecture underlying variation in the timing of FMT consists of multiple QTL, each with moderate to small effect. By integrating the results of Chapter 1 and 3, I have also been able to generate the first list of candidate genes that may participate in the regulation of FMT timing.