title: S1-Type Endonuclease 2 in Dedifferentiating Arabidopsis Protoplasts: Translocation to the Nucleus in Senescing Protoplasts Is Associated with De-Glycosylation.
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.
authors.affiliation: French Associates Institute of Agriculture and Biotechnology of Drylands, The Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
authors.forename: Yemima
authors.initials: Y
authors.lastname: Givaty-Rapp
authors.affiliation: French Associates Institute of Agriculture and Biotechnology of Drylands, The Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
authors.forename: Narendra Singh
authors.initials: NS
authors.lastname: Yadav
authors.affiliation: French Associates Institute of Agriculture and Biotechnology of Drylands, The Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
authors.forename: Asif
authors.initials: A
authors.lastname: Khan
authors.affiliation: French Associates Institute of Agriculture and Biotechnology of Drylands, The Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
authors.forename: Gideon
authors.initials: G
authors.lastname: Grafi
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D016922:Cellular Senescence / Q000235:genetics; D002503:Centromere / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D032461:Chromosomes, Plant; D004720:Endonucleases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D006031:Glycosylation; D009154:Mutation; D021381:Protein Transport; D011523:Protoplasts / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D002843:Chromatin; C574857:ENDO2 protein, Arabidopsis; D004720:Endonucleases