EARLY IN SHORT DAYS 7(ESD7) encodes the catalytic subunit of DNA polymerase epsilon and is required for flowering repression through a mechanism involving epigenetic gene silencing

Abstract

SUMMARYWe have characterized a mutation affecting the Arabidopsis EARLY IN SHORT DAYS 7 (ESD7) gene encoding the catalytic subunit of DNA polymerase epsilon (e), AtPOL2a. The esd7-1 mutation causes early flowering independently of photoperiod, shortened inflorescence internodes and altered leaf and root development. esd7-1 is a hypomorphic allele whereas knockout alleles displayed an embryo-lethal phenotype. The esd7 early flowering phenotype requires functional FT and SOC1 proteins and might also be related to the misregulation of AG and AG-like gene expression found in esd7. Genes involved in the modulation of chromatin structural dynamics, such as LHP1/TFL2 and EBS, which negatively regulate FT expression, were found to interact genetically with ESD7. In fact a molecular interaction between the carboxy terminus of ESD7 and TFL2 was demonstrated in vitro. Besides, fas2 mutations suppressed the esd7 early flowering phenotype and ICU2 was found to interact with ESD7. Discrete regions of the chromatin of FT and AG loci were enriched in activating epigenetic marks in the esd7-1 mutant. We concluded that ESD7 might be participating in processes involved in chromatin-mediated cellular memory.

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

“…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). Nevertheless, the genetic data suggest that there exists a tight link between DNA-pols and an LHP1-associated PRC2.…”

“…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.…”

“…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).…”

Regulating DNA Replication in Plants

“…Plant POLE has been studied in Arabidopsis and rice, including genetic analyses that have not been performed in other multicellular organisms (Jenik et al 2005;Ronceret et al 2005;Yin et al 2009;del Olmo et al 2010). Arabidopsis POLE holoenzyme possesses two catalytic subunits (POLE1A and POLE1B, also called AtPOL2a and AtPOL2b), and the regulatory subunits POLE2 (or DPB2), DPB4, and DBP3a.…”

“…Genes encoding the POLE3 and POLE4 subunits belong to a multigenic family and are difficult to identify unambiguously in the Arabidopsis genome. Hypomorphic mutants of POLE1 (esd7/abo4/ til1) show an early flowering phenotype because of changes in the expression of key flowering genes, a process that occurs through a genetic interaction of POLE1 with LHP1 (LIKE-HET-EROCHROMATIN PROTEIN1) (Yin et al 2009;del Olmo et al 2010). …”