Epigenetic regulation of gene expression is relatively new and rapidly developing research
field, which studies the different mechanisms of regulation of gene expression that even
though are heritable, are independent of changes in the DNA sequence and certainly aid to
the complexity of the regulation of gene expression and provide fine tuning mechanisms to
the process.
Now it is known that many essential processes such as: development, signaling, innate
immunity, symbiosis, etc. in plants are epigenetically regulated. We were interested in the
epigenetic regulation of the cell’s specialization and differentiation process and were
aiming to investigate the existence of a tissue-specific epigenetic code. We designed a
forward genetic screen, based on a tissue-specific GFP reporter line- silex, which reports on
the epigenetically regulated developmental dene APUM9 in Arabidopsis thaliana. The silex
reporter line was properly reporting on the endogenous APUM9 (Chapter 2). Of the
numerous mutant lines that we recovered in the mutant screen, in this thesis two epigenetic
regulators are presented.
First a new allele of the well-known histone deacetylase HDA6 was recovered and it was
found that this protein had separable activities in the euchromatin and the heterochromatin
(discussed in 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 was validated. Furthermore the assessment of the transcripts present in the
different cell compartments- nucleus and cytoplasm, revealed an export bias towards
antisense RNAs (asRNAs), suggesting that the selectivity of the export process in plants is
dependent on AtSAC3B (Chapter 3). Taken together 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).