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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 epsilon. 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) approximately 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/M-specific 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.
Highlights
Plants are sessile and unable to escape acute environmental stresses, but they have developed sophisticated responses to cope with and survive stress conditions
We found that the mutation in ABO4/POL2a/TIL1 releases transcriptional gene silencing (TGS) in some genomic regions and greatly increases the frequency of somatic homologous recombination (HR); both effects were reinforced by abscisic acid (ABA) treatment
We found a clear increase of H3K27me3 in the first intron regions of FLOWERING LOCUS C (FLC) (FLC-P3 and FLC-P5, two fragments amplified by PCR; please see Cao et al, 2008), but only a little decrease in the promoter region of FLOWERING LOCUS T (FT) in abo4-1 compared to the wild type (Figure 7P, top)
Summary
Plants are sessile and unable to escape acute environmental stresses, but they have developed sophisticated responses to cope with and survive stress conditions. Plants are able to quickly counteract environmental stresses through actions, such as up- or downregulating gene expression and accumulating adaptive metabolic compounds. Abiotic stresses, such as drought, high salinity, and low temperature, induce the accumulation of the phytohormone abscisic acid (ABA) (Finkelstein et al, 2002; Koornneef et al, 2002). Studies far have focused on ABA-mediated rapid physiological responses that are important for plant stress resistance in the short term. Whether ABA or an ABA-regulated signal can affect epigenetic states and genome stability, which might be important for the long-term adaptation of plants to environmental stresses and possibly contribute to plant evolution, is not known
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