| dc.description.abstract | Wood, or secondary xylem, is formed during secondary growth and serves as a structural element as well as part of a plants vascular system. Secondary xylem is largely comprised of cells with lignified secondary cell walls to which the rigidity of the tissue is attributed. Secondary growth is observed throughout the plant kingdom but is most prominent in trees. Trees are seed-producing, vascular plants that are divided into two groups based on their method of reproduction: angiosperms and gymnosperms. Most tree species belong to the group of flowering plants, the angiosperms, which are estimated to have evolved 200 million years after the first gymnosperms. Despite this ancient divergence, wood formation as a phenotype is conserved between the gymnosperms and angiosperms. Much is understood about the various processes involved in secondary growth, but little is known about the more ancient, underlaying mechanisms governing wood formation. For this thesis, high-resolution transcriptomics was used to capture the similarities in wood formation across three gymnosperm species and three angiosperm species. Orthologs conserved between the pairs of species were identified using co-expression network analysis, thereby combining similarity in molecular function with biological function. Orthologs conserved across all pairs of species were identified using sub-networks, cliques. The genes conserved across all species were involved in various processes associated with secondary growth, and certain genes were suggested as marker gene candidates for the various tissues. These genes included homologs of PHLOEM PROTEIN2 (PP2), CELL DIVISION CONTROLL2 (CDC2) and transcription factors for formation of actin filaments. | |
