Molecular systematics, floral evolution, and MADS-BOX gene characterization in basal angiosperms.

摘要

The objectives of my research involving basal angiosperms were: (1) to resolve phylogenetic relationships; (2) to explore patterns of perianth evolution; and (3) to characterize B class genes from two of the earliest diverging angiosperms, Nuphar and Illicium.; I used a compartmentalization approach to explore phylogenetic relationships among the deepest nodes of the angiosperms using both maximum parsimony and maximum likelihood methods (Chapter One). The tree that I obtained was used as a framework to investigate perianth evolution. More specifically, perianth phyllotaxis, merosity (number of parts), and differentiation was examined. Perianth character states were mapped using equally weighted parsimony. Perianth phyllotaxis appeared to be equivocal throughout much of the tree. The mapping of perianth merosity indicates that the trimerous perianth may be an ancestral or primary formula for basal angiosperms. Many of the deepest nodes of the tree are equivocal in the mapping of perianth differentiation, and the differentiated perianth appears to have evolved several times in different lineages.; Chapter Two involved an analysis of the root of the angiosperms. I found that the monotypic genus Amborella continues to receive strong bootstrap support as the sister to all other extant angiosperms, however, using the likelihood ratio test and parametric bootstrapping, I found that I could not reject Amborella vs. Amborella + Nymphaeales as sister to all other angiosperms based on likelihood methods of phylogenetic inference (Chapter 2).; Lastly, virtually nothing is known about the conservation of the genetic pathways underlying floral development (ABC model) in basal angiosperms. Hence, a survey of B class genes in a few critical basal lineages is an important first step (Chapter 3). To this end, I isolated and characterized B class genes from Nuphar and Illicium. Elucidating the genetics of floral development in these key lineages not only will help to answer questions regarding the origin and diversification of the flower itself, but will also provide the opportunity to link what is known about derived eudicot model systems with other flowering plants, providing a comprehensive picture of floral development and evolution. I found that the B class genes isolated from Nuphar and Illicium are similar to B class genes isolated from other basal angiosperms. Preliminary gene expression data from Nuphar suggests that these genes are expressed in perianth, staminodes, stamens, and carpels.