Abstract
Cell dedifferentiation characterizes the transition of leaf cells to protoplasts and is accompanied by global chromatin decondensation. Here we show that in Arabidopsis, chromocentric chromatin undergoes prompt and gradual decondensation upon protoplasting. We hypothesized that prompt chromatin decondensation is unlikely to be driven solely by epigenetic means and other factors might be involved. We investigated the possibility that S1-type endonucleases are involved in prompt chromatin decondensation via their capability to target and cleave unpaired regions within superhelical DNA, leading to chromatin relaxation. We showed that the expression and activity of the S1-type endonuclease 2 (ENDO2) is upregulated in dedifferentiating protoplasts concomitantly with chromatin decondensation. Mutation of the ENDO2 gene did not block or delay chromocentric chromatin decondensation upon protoplasting. Further study showed that ENDO2 subcellular localization is essentially cytoplasmic (endoplasmic reticulum-associated) in healthy cells, but often localized to the nucleus and in senescing/dying cells it was associated with fragmented nuclei. Using in gel nuclease assays we identified two ENDO2 variants, designated N1 (cytoplasmic variant) and N2 (cytoplasmic and nuclear variant), and based on their capability to bind concanavalin A (ConA), they appear to be glycosylated and de-glycosylated (or decorated with ConA non-binding sugars), respectively. Our data showed that the genome is responding promptly to acute stress (protoplasting) by acquiring decondensation state, which is not dependent on ENDO2 activity. ENDO2 undergoes de-glycosylation and translocation to the nucleus where it is involved in early stages of cell death probably by introducing double strand DNA breaks into superhelical DNA leading to local chromatin relaxation and fragmentation of nuclei.
Highlights
IntroductionSomatic plant cells retain their developmental capabilities and under appropriate conditions can dedifferentiated (i.e., assume stem cell like state) and give rise to different cell types thatPLOS ONE | DOI:10.1371/journal.pone.0170067 January 9, 2017Endonuclease 2 Involves in Early Stages of Cell Death make up a new fertile plant
Somatic plant cells retain their developmental capabilities and under appropriate conditions can dedifferentiated and give rise to different cell types thatPLOS ONE | DOI:10.1371/journal.pone.0170067 January 9, 2017Endonuclease 2 Involves in Early Stages of Cell Death make up a new fertile plant
The results clearly showed that the pericentric region is the first to undergo decondensation followed by decondensation of the centromeric region (CEN180), which is evident after 60 min of protoplasting
Summary
Somatic plant cells retain their developmental capabilities and under appropriate conditions can dedifferentiated (i.e., assume stem cell like state) and give rise to different cell types thatPLOS ONE | DOI:10.1371/journal.pone.0170067 January 9, 2017Endonuclease 2 Involves in Early Stages of Cell Death make up a new fertile plant. Somatic nuclei derived from chicken erythrocytes were induced to dedifferentiate by Xenopus egg extract, which was accompanied by prompt chromatin decondensation [6] This suggests that besides epigenetic means other mechanisms might be involved to bring about prompt acquisition of decondensed chromatin state. Torsional strain generated in superhelical DNA, which is common in condensed chromatin often leads to local denaturation and unpairing [7], which allows single-stranded DNA endonucleases to generate nicks and/or DSBs to bring about chromatin relaxation. This is well demonstrated by the conversion of supercoiled plasmid DNA into relaxed and linear forms by S1-type endonucleases [8,9]
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