Epigenetic Regulation, Somatic Homologous Recombination, and Abscisic Acid Signaling Are Influenced by DNA Polymerase ϵ Mutation inArabidopsis   

Abstract

Based on abscisic acid (ABA) inhibition of seed germination and seedling growth assays, we isolated an ABA overly sensitive mutant (abo4-1) caused by a mutation in the Arabidopsis thaliana POL2a/TILTED1(TIL1) gene encoding a catalytic subunit of DNA polymerase «. The dominant, ABA-insensitive abi1-1 or abi2-1 mutations suppressed the ABA hypersensitivity of the abo4-1 mutant. The abo4/til1 mutation reactivated the expression of the silenced Athila retrotransposon transcriptional silent information (TSI) and the silenced 35S-NPTII in the ros1 mutant and increased the frequency of somatic homologous recombination (HR) ;60-fold. ABA upregulated the expression of TSI and increased HR in both the wild type and abo4-1. MEIOTIC RECOMBINATION11 and GAMMA RESPONSE1, both of which are required for HR and double-strand DNA break repair, are expressed at higher levels in abo4-1 and are enhanced by ABA, while KU70 was suppressed by ABA. abo4-1 mutant plants are sensitive to UV-B and methyl methanesulfonate and show constitutive expression of the G2/Mspecific cyclin CycB1;1 in meristems. The abo4-1 plants were early flowering with lower expression of FLOWER LOCUS C and higher expression of FLOWER LOCUS T and changed histone modifications in the two loci. Our results suggest that ABO4/POL2a/TIL1 is involved in maintaining epigenetic states, HR, and ABA signaling in Arabidopsis.

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

“…of the core DNA-replication proteins, including the DNA single-strand-binding protein RPA2A (Xia et al, 2006), Pola (Liu et al, 2010a), Pol « (Yin et al, 2009), POLD2 (this study), RFC1 (Liu et al, 2010b), and TOUSLED protein kinase (Wang et al, 2007). Other studies have identified other DNA replication-related proteins involved in mediating TGS, including BRU1 (Takeda et al, 2004), chromatin assembly factor (CAF-1) subunits FAS1 and FAS2 (Ono et al, 2006;Schonrock et al, 2006), and TEBICHI (Inagaki et al, 2009).…”

“…However, pold2-1 had little effect on the ProRD29A:LUC locus in dms3-4. Like mutants of DNA replication-related proteins (Elmayan et al, 2005;Xia et al, 2006;Yin et al, 2009;Liu et al, 2010aLiu et al, , 2010b, pold2-1 failed to suppress the silenced ProRD29A:LUC in the ros1-1 mutant (Fig. 1F).…”

“…1C). TSIs are endogenous TGS loci (Steimer et al, 2000), the expression of which is altered in some mutants involved in DNA methylation, histone modification, or DNA replication (Steimer et al, 2000;Xia et al, 2006;Yin et al, 2009;Liu et al, 2010aLiu et al, , 2010b. The expression of TSIs was increased in these isolated mutants (Fig.…”

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). …”