Thesis (Ph. D.)--University of Chicago, 1908? / "Reprinted from the Botanical gazette, vol. XLV, no. 5." Includes bibliographical references (p. 312-316) Also available on the Internet.

The life cycle of land plants alternates between the haploid gametophyte and the diploid sporophyte generations. Asexual reproductive strategies, that bypass meiosis and fertilization, have evolved in diverse land plant taxa. Apogamy is one such strategy that produces a sporophyte directly from a gametophyte cell. The genes that drive the process of apogamy are unknown. Knowledge of these genes and their functions will provide insight into the evolution of asexual reproduction, the sporophyte body plan and the alternation of generations in land plants. My Ph. D. research has focused on identifying the genes function in apogamy commitment, and understanding the functions of their counterparts in angiosperms. First, I successfully induced apogamy from the fern Ceratopteris richardii and discovered that the gametophytes begin to become committed to apogamy after 10 days of culture on inductive medium. I then created a cDNA library that represents genes with enhanced expression during commitment. Comparison of the Gene Ontology terms mapped to this cDNA library with that of the gametophyte transcriptome of the fern Pteridium aquilinum showed that this library is enriched in genes that function in stress response and metabolism. This library contains many sequences whose homologues in Arabidopsis are specifically expressed or upregulated in flower organs or seed structures, both of which are absent in ferns. One of these genes, UNC93-like, is expressed in the eggs of C. richardii gametophytes, as evidenced by in situ hybridization. Functional egg cells are implicated as necessary for C. richardii gametophytes to undergo apogamy. In Arabidopsis, an AtUNC93-like mutant, which produces a partial AtUNC93-like transcript, has vegetative and reproductive defects. Embryo abortion and gametophyte lethality contribute to a small seed set in these plants. Reciprocal crosses indicate that the mutant allele does not affect gametophyte function but cause a maternal failure to maintain viability of all gametophytes. Thus, the AtUNC93-like gene is necessary for normal sporophyte vegetative growth and reproductive success, but is dispensable for the direct function of gametophytes. My research has provided insight into the mechanisms that induce apogamy in a fern. The apogamy library is a valuable resource for future investigations into apogamy.

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1909. / Cover title. "Reprinted from Volume XVII, Part I of the Transactions of the Wisconsin Academy of Sciences, Arts, and Letters." Includes bibliographical references (p. 49-56).

A dissertation submitted to the faculty of science university of the Witwatersrand, Johannesburg for the Degree of Master of Science Johannesburg 1992 / The gametophyte generation of the fern life cycle is initiated with the formation of spores. The spores of C. viridis (Fonsic) Swarts var. glaeca (Sim) schelp Anthony are trilete and have a cristate spore wall ornamentation. Under favourable conditions the spores of C. viridis var. glauca show polar germination [Abbreviated Abstract. Open document to view full version] / GR2017

The life cycle of all land plants is characterized by the alternation between two multicellular generations: haploid gametophytes and diploid sporophytes. Whereas meiotic recombination and fertilization via sexual reproduction is known to confer adaptive evolutionary benefits, some plant species can reproduce asexually bypassing meiosis and fertilization yet still undergo alternation of generations. In ferns, the two asexual reproductive pathways are termed apogamy and apospory, i.e. the asexual reproduction of sporophytes and gametophytes, respectively. Although understanding the process of asexual reproduction in flowering plants would be of considerable agricultural value, the molecular mechanisms underlying this process have yet to be identified. Similarly, the genes in ferns that underlie apogamy and apospory are unknown. Knowledge of such genes will provide invaluable information not only for the evolutionary study of asexual reproduction in land plants, but also insight into the developmental program for each generation. My PhD research focuses on the investigation of candidate genes involved in asexual reproduction in the model fern Ceratopteris richardii. Though the molecular mechanisms underlying asexual reproduction are not understood, it is hypothesized that asexual reproduction is the result of altered regulation of certain sexual reproduction-related genes. Therefore, I selected candidate genes for asexual reproduction in C. richardii, CrEMS1, CrKNOX3 and CrANT, based on the functions of their respective homologs during sexual reproduction in two other model systems: Arabidopsis thaliana and Physcomitrella patens. I showed that, in C. richardii, CrEMS1 is expressed during key events of sexual reproduction, including sporogenesis, gametogenesis and embryo development; CrKNOX3 expression is specific for the mature egg cells and CrANT expression is restricted to sperm cells. The presence of CrEMS1 during early embryo development made it a suitable candidate for an embryonic marker for future research. To study the function of the candidate genes, I overexpressed CrKNOX3 and BnBBM, a flowering plant BBM gene that has similar expression patterns in Brassica to CrANT. The overexpression of CrKNOX3 results in unique cell outgrowth from the antheridia, and overexpression of BnBBM results in spontaneous apogamy induction. Whole mount in situ also showed CrEMS1 expression, marking embryonic identity, in pre-apogamous cells undergoing sugar-induced and overexpression of BnBBM-induced apogamy. The results of my PhD research provides, for the first time, insight into the molecular mechanisms underlying asexual reproduction in the model fern C. richardii, and invaluable tools, transient and stable Agrobacterium-mediated transformation protocols, for functional genomics research in this fern. The spontaneous apogamy induction on BnBBM-expressing gametophytes and the presence of CrEMS1 in pre-apogamous cells confirm the hypothesis that asexual reproduction is the result of the alteration in expression of sexual-related genes, verifying that the two pathways share a common set of genes.

Hybridization is an important mechanism in diversification. It often makes taxonomy difficult. Lack of strong supported intrageneric classification in genus Pteris (Pteridaceae) could be caused by natural hybridization. Most hybridization documnted in Pteris was based on limited evidence. This study focuses on Pteris cadieri complex, the taxon with putative hybridization. The species complex displayed significant morphological variation and was associated with hybrid origin. Reproductive biology revealed variation in spore number per sporangium, spore size, spore shape and apogamous reproduction, which imply its hybrid origin. Cytology analysis using chromosome counting and flow cytometry identified diploids, triploids, and tetraploids. CpDNA and nuclear DNA supported that Pteris cadieri complex is hybrid origin: paternal and maternal lineages were inferred and 11 taxa were identified. Furthermore, comparing materials form Hainan and Taiwan, , it is clear that the species complex is composed by taxa arisen from multiple hybridization. Systematic inconsistency existed between chloroplast and nuclear phylogenies in Pteris impled that other taxa might have involved in hybridization events, in addition to the Pteris cadieri complex. Hybridization may be very common in Pteris. To infer intrageneric taxonomy of Pteris, effect of reticulate evolution should never be neglected. Finally, based on morphological and evolutionary traits, the taxonomy of Pteris cadieri complex is revised. There are Pteris cadieri Christ, Pteris dimorpha Copel. var. dimorpha, Pteris dimorpha var. plumbea (Christ) Y.-S. Chao, H.-Y. Liu & W.-L. Chiou, Pteris grevilleana Wall. ex Agardh var. grevilleanan, Pteris grevilleana Wall. ex Agardh var. ornata Alderw., and Pteris hainanensis Ching.