Gene expression variation and buffering mechanisms in Arabidopsis thaliana

Non-genetic variability in gene expression is an inevitable consequence of the stochastic nature of processes driving transcription and translation, as well as the epigenetic modifications of the genome. This phenomenon has been observed in both unicellular and multicellular organisms. Largely thought to be deleterious to cell fitness, it is not uniform across the transcriptome. This implies the existence of mechanisms regulating expression variability, although they, and the role played by inter-individual expression variability, remain poorly researched in multicellular systems. I utilised multiple Arabidopsis thaliana time series expression datasets to identify variable genes and analyse their cellular functions. I show that variable genes are enriched for Gene Ontology terms related to biotic and abiotic stress response and that, inversely, low variability genes are enriched for housekeeping terms. Moreover, I also investigated DNA methylation as a potential mechanism buffering expression variability by analysing methylation of Arabidopsis genes and promoters, and by comparing wild type plants with CG methylation reduction and CG methylation loss methyltransferase mutant specimens. I found that variable genes are less methylated in the CG context in wild type Arabidopsis. Loss of CG methylation alters expression variability of some genes. Of those, significantly greater portion of genes gained variability, compared to those that lost it. These results are an important step towards greater understanding of these processes in multicellular organisms, and their role.