Characterization and Expression of FRIEND OF LEAFY1 (FOL1) in the male gametophyte of Arabidopsis thaliana

In this thesis, I examined the function of FOL1 in male gametophytic development. Inspection of the effects of FOL1 mutants on the gametophyte are important to understanding the role of the protein in Arabidopsis thaliana development. In order to understand its function, a clear picture of its expression pattern in the gametophyte is needed. FOL1p::GFP plants were used to examine FOL1 expression during pollen development. In addition, pollen viability was examined. We conclude the FOL1 is necessary for pollen development. Use of Arabidopsis thaliana as a model organism Research conducted on plants is vital for our understanding of eukaryotes and has applications for improvement of food crops. Angiosperms, plants that produce flowers and seeds, are a diverse group of plants and encompass most agricultural crops. A. thaliana is used as a plant model organism due to its ease of manipulation, easy growth requirements, knowledge of the genome, and its similarities with other angiosperms. A. thaliana is in the mustard family, with notable food crop relatives being broccoli, kale, and cabbage. A. thaliana has a relatively rapid life cycle. Seed to seed is typically achieved within eight weeks. The compact nature of the plant allows for large numbers of plants to be grown. It produces an abundance of flowers resulting in a large amount of progeny. The plant is also easily transformed through the use of Agrobacterium tumefaciens. Important to molecular genetics, the entire genome was sequenced in 2000 (The Arabidopsis Genome Initiative, 2000), allowing genes to be pinpointed within the genome and on the chromosomes. 2 Alteration of generations in higher plants The life cycle of plants is unique within the eukaryotic kingdom. All land plants have an alteration of generations in which they go through a sporophyte stage and a gametophyte stage (Figure 1). The diploid sporophyte produces haploid spores through meiosis. These haploid cells are the gametophyte stage and form multicellular structures through mitotic divisions. Egg and sperm cells differentiate within these multicellular structures. Once the sperm and egg combine they form the zygote, restoring the diploid sporophyte stage. In both angiosperms and gymnosperms, the sporophyte composes all visible parts of the plant. The gametophyte is surrounded by diploid tissue and relies on the sporophyte for nutrients and protection. Anther and Pollen Development in A. thaliana Anther and pollen development are fundamental for angiosperm reproduction and comprise the male reproductive structure. The production of pollen, the male gametophyte, is done within pollen sacs. There are four pollen sacs per anther and they make up the microsporangium. Pollen and anther development are relatively well studied and demarcated into 15 stages (Table 1), beginning with the emergence of stamen primordia and ending with stamen dehisence (Sanders et al., 1999). The process of pollen development and maturation in the anthers of A. thaliana begins with cells of the primary sporogenous layer undergoing mitosis (stage 3), forming diploid meiocytes (microspore mother cells, MMC.) The meiocytes then enter meiosis (Fig. 2) to form tetrads: four haploid immature pollen cells surrounded by the MMC cell wall (stage 6). After formation of tetrads, the sporophyte tapetum surrounding the gametophytes releases beta-(1,3) glucanase, resulting in the degradation of the the MMC wall and releasing the microspores into