The nuclear pore complex : its role in chromatin structure and RNA export

Epigenetic regulation of gene expression is a relatively new and rapidly developing research field. It studies the mechanisms of regulation of gene expression, which although heritable, occur independently of changes in the DNA sequence and certainly aid to the complexity of the this process and provide fine tuning to it.
Now, it is known that many essential processes in plants such as: development, signaling, innate immunity, symbiosis, etc. are epigenetically regulated. However, little is known about the epigenetic regulation of cell’s specialization and differentiation. Here, we postulate the existence of a tissue-specific epigenetic code. This study consists primarily of a forward genetic screen, based on a tissue-specific GFP reporter line- silex, which reports adequately on the epigenetically regulated developmental gene APUM9 in Arabidopsis thaliana (Chapter 2). Of the numerous mutant lines that we recovered in the mutant screen, two epigenetic regulators are presented in this thesis.
First, a new allele of the well-known histone deacetylase HDA6 was recovered and it was found that this protein has separable activities in the euchromatin and the heterochromatin (Chapter 2). The second mutant was found to be defective in AtSAC3B, a nuclear pore associated protein, which up until now hasn’t been associated with epigenetic regulation of gene expression. The homologues of AtSAC3B in different model organisms are involved in nuclear-cytoplasmic export of mRNAs. By using different mutant alleles of AtSAC3B for studying the nuclear-cytoplasmic export, the requirement of the protein in the process in plants was validated. The assessment of the transcripts present in the different cell compartments, nucleus and cytoplasm of the mutant, revealed an export bias towards antisense RNAs (asRNAs), suggesting that the selectivity of the export process in plants is dependent on AtSAC3B (Chapter 3). This indicated that AtSAC3B is an important player in the regulation of gene expression through its’ selectivity in the RNA export process. Likewise the nuclear pore complex that is known to influence the chromatin organization, the studies on the chromatin organization and the dynamics of selected histones modifications in atsac3b, revealed the importance of AtSAC3B for the heterochromatin organization in plants (Chapter 4).