The Arabidopsis DNA Polymerase δ Has a Role in the Deposition of Transcriptionally Active Epigenetic Marks, Development and Flowering

Abstract

DNA replication is a key process in living organisms. DNA polymerase α (Polα) initiates strand synthesis, which is performed by Polε and Polδ in leading and lagging strands, respectively. Whereas loss of DNA polymerase activity is incompatible with life, viable mutants of Polα and Polε were isolated, allowing the identification of their functions beyond DNA replication. In contrast, no viable mutants in the Polδ polymerase-domain were reported in multicellular organisms. Here we identify such a mutant which is also thermosensitive. Mutant plants were unable to complete development at 28°C, looked normal at 18°C, but displayed increased expression of DNA replication-stress marker genes, homologous recombination and lysine 4 histone 3 trimethylation at the SEPALLATA3 (SEP3) locus at 24°C, which correlated with ectopic expression of SEP3. Surprisingly, high expression of SEP3 in vascular tissue promoted FLOWERING LOCUS T (FT) expression, forming a positive feedback loop with SEP3 and leading to early flowering and curly leaves phenotypes. These results strongly suggest that the DNA polymerase δ is required for the proper establishment of transcriptionally active epigenetic marks and that its failure might affect development by affecting the epigenetic control of master genes.

The second subunit of DNA-polymerase delta is required for genomic stability and epigenetic regulation

“…SEP3 was recently reported to be a target of the catalytic subunit POLD1, and its H3K4me3 level is increased in the pold1 mutant (Iglesias et al, 2015). Consistent with our ChIP data (Fig.…”

“…DNA Pol d is conserved in eukaryotes and is important in regulating genomic stability and development in Arabidopsis (Schuermann et al, 2009;Iglesias et al, 2015). To our knowledge, the biological functions of Arabidopsis POLD2 have not been studied yet.…”

“…These results suggest that POLD2 does not affect the expression of genes for establishment and maintenance of H3K4me3 and H3K27me3 modification, or the global H3K4me3 and H3K27me3 levels. It was previously proposed that DNA polymerase d may play a role in preventing replication stress or HR and in depositing active H3K4me3 marks (Iglesias et al, 2015). Meanwhile, some studies indicate that the catalytic subunit of DNA polymerase a interacts with (Barrero et al, 2007) or perturbs the binding of like-heterochromatin protein 1 (LHP1; Hyun et al, 2013), which is the main reader/effector for H3K27me3 in Arabidopsis (Barrero et al, 2007;Zhang et al, 2007).…”

Ctf4-related protein recruits LHP1-PRC2 to maintain H3K27me3 levels in dividing cells in Arabidopsis thaliana

“…Mutations in INCURVATA (ICU) 2 and EARLY IN SHORT DAYS (ESD) 7, respectively encoding homologs of the priming DNA-polα and the leading strand-specific DNA-pole, were shown to enhance both lhp1 and clf mutant phenotypes (25)(26)(27). Similar genetic interaction was suggested by the observation that a temperature-conditional DNA-polδ mutant, gigantea suppressor (gis) 5, expresses increased levels of SEPPALATA (SEP) 3 and FLOWERING LOCUS T (FT), which are also up-regulated in lhp1 and clf mutants (28). Physical interaction between LHP1 and ESD7 or ICU2 was shown by in vitro pull-down (25,26), but the latter could not be confirmed in a later study (27).…”

“…Mutations in the three DNA-pols enhance the abnormal phenotype of PcG mutants or cause deregulated expression of PcG target genes (25)(26)(27)(28). Although evidence for a direct interaction of LHP1 with ICU2 is slightly conflicting (25,27), it is conceivable that these proteins, which engage in higher-order protein complexes, possess several interfaces to other proteins.…”