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.

Dead Pericarps of Dry Fruits Function as Long-Term Storage for Active Hydrolytic Enzymes and Other Substances That Affect Germination and Microbial Growth

“…Presently, the role played by nucleases in seed germination and seedling establishment is unknown. Generally, endonucleases appear to be involved in multiple cellular processes including DNA synthesis and repair [ 28 ], as well as in fragmentation of genomic DNA during cell death [ 29 , 30 , 31 ]. The findings that endonucleases are capable of introducing nicks and double strand DNA breaks into superhelical DNA [ 32 , 33 ] suggest a possible role defense against plasmid-bearing soil pathogens such as the Clavibacter michiganensis subsp.…”

From Single Cell to Plants: Mesophyll Protoplasts as a Versatile System for Investigating Plant Cell Reprogramming

“…This condensation is accompanied by a reduction in the scavenging capacity of reactive oxygen species (ROS) [73], which leads to an increased ROS accumulation [74,75]. Recently, the presence of chromatin condensation has also been demonstrated during protoplast isolation followed by subsequent cultivation in a buffer without PGRs [76].…”

The Dead Can Nurture: Novel Insights into the Function of Dead Organs Enclosing Embryos

“…The proteome data also revealed S1 type endonucleases, which are released from DOEEs upon hydration [ 16 , 20 , 21 ]. Endonucleases, in general, are involved in multiple cellular processes including DNA synthesis and DNA repair [ 31 ] and in PCD [ 32 , 33 , 34 ]. The capacity of endonucleases to target unpaired regions within superhelical DNA to introduce nicks and double strand DNA breaks may implicate them as defense factors against plasmid-containing soil pathogens such as the Clavibacter michiganensis subsp.…”