Examination of epigenetic control mechanisms and the genetic characterization of vegetative class profilins in Arabidopsis thaliana
Mussar, Kristofer Joseph
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The dynamic nature of the actin cytoskeleton is maintained through interactions with a suite of different Actin Binding Proteins (ABPs) that remodel actin filaments. One such ABP, profilin, is believed to promote both actin filament polymerization and depolymerization via the binding and sequestering of globular actin (G-actin) monomers. In Arabidopsis thaliana, profilin is encoded by a five-member gene family that contains two distinct subclasses, vegetative and reproductive. PRF1, PRF2, and PRF3 are expressed in all vegetative tissues, while PRF4 and PRF5 are specifically expressed only in reproductive tissues. The goal of this study was to characterize the three vegetative members in terms of their roles in plant cell and organ development. Using a collection of T-DNA insertion mutants and RNAi knockdowns targeting individual and combinations of PRF1, PRF2, and PRF3, I found that each of these three variants gave rise to specific developmental deficiencies. Plants lacking profilins had defects in rosette leaf morphology, inflorescence stature, petiole elongation, and lateral root initiation and growth. Microscopic examination of these dwarfed plants lacking in profilin variants indicated that they have smaller cells defective in cell elongation. Evidence is presented that mixtures of independent function, quantitative genetic effects, and functional redundancy have preserved the three vegetative profilin genes. I also explore the possibility of DNA sequence guiding various epigenetic control mechanisms. My efforts focus on understanding how sequence facilitates the epigenomic landscape of histone post-translational modifications (PTMs). Through interpretation of PTM deposition data at the gene and gene family level, I discovered that recently duplicated gene sequences exhibit varying levels of conservation across their histone modification enrichment profiles. These data suggest that epigenetic controls aid “evolution by gene duplication” by silencing some recent gene duplicates, but not others, until beneficial mutations and subfunctionalization can occur. By searching for correlations among these enrichment profiles I was able to detect combinatorial patterns of histone modification marks within each gene family. Distinct patterns containing known activation marks that are cooperatively interacting were found in gene families where sequence was more conserved, suggesting that sequence may be playing some role in facilitating PTM deposition throughout the genome.