A Phylogenetic Investigation into the Evolutionary History of Stomata and Land Plants

• Main Author: Harris, Brogan J
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Genes; Genetics; Phylogenetics

The origin of land plants was accompanied by new adaptations to life on land, including the evolution of stomata - pores on the surface of plants that regulate gas exchange. The genes that underpin the development and function of stomata have been extensively studied in model angiosperms such as Arabidopsis thaliana. However, little is known about stomata in bryophytes and other early diverging lineages, as a result their evolutionary origins and ancestral function remain poorly understood. The lack of consensus regarding stomatal evolution can partly be ascribed to the evolutionary history of land plants also being uncertain, most notably the position of the bryophytes. Here, I resolve the position of bryophytes in the land plant tree using a multitude of phylogenetic techniques, trace the evolutionary history of stomatal associated genes, and reconstruct the gene content of the ancestral land plant. The results presented in this thesis suggest that bryophytes form a monophyletic group. The analysis of stomatal-associated genes in the light of bryophyte monophyly revealed that the genes were more ancient than previously appreciated. The analysis shows that a range of core guard cell genes trace back to the common ancestor of all embryophytes. These analyses suggest that the first embryophytes possessed stomata that were more sophisticated than previously envisioned, and that the stomata of bryophytes have undergone reductive evolution, including their complete loss in the liverwort lineage. Analysis of ancestral gene content revealed that the first embryophytes were more complex than stem bryophytes - that is, reductive evolution is not exclusive to stomatal-associated genes, but affects the genes encoding many functional and developmental pathways in bryophyte genomes. Contemporary lineages of embryophytes have diversified substantially along distinct trajectories, resulting in significant genomic disparity between extant bryophytes and tracheophytes.