The Structure-Specific Endonucleases MUS81 and SEND1 Are Essential for Telomere Stability in Arabidopsis

Abstract

Structure-specific endonucleases act to repair potentially toxic structures produced by recombination and DNA replication, ensuring proper segregation of the genetic material to daughter cells during mitosis and meiosis. Arabidopsis thaliana has two putative homologs of the resolvase (structure-specific endonuclease): GEN1/Yen1. Knockout of resolvase genes GEN1 and SEND1, individually or together, has no detectable effect on growth, fertility, or sensitivity to DNA damage. However, combined absence of the endonucleases MUS81 and SEND1 results in severe developmental defects, spontaneous cell death, and genome instability. A similar effect is not seen in mus81 gen1 plants, which develop normally and are fertile. Absence of RAD51 does not rescue mus81 send1, pointing to roles of these proteins in DNA replication rather than DNA break repair. The enrichment of S-phase histone g-H2AX foci and a striking loss of telomeric DNA in mus81 send1 further support this interpretation. SEND1 has at most a minor role in resolution of the Holliday junction but acts as an essential backup to MUS81 for resolution of toxic replication structures to ensure genome stability and to maintain telomere integrity.

Resolvase OsGEN1 Mediates DNA Repair by Homologous Recombination

“…S2C). A very recent report showed that in Arabidopsis, SEND1 but not GEN1 acts as the functional Yen1/GEN1 homolog and plays an important role in toxic replication intermediate repair and telomere homeostasis in the absence of MUS81 (Olivier et al, 2016). In our study, we demonstrated that OsGEN1 but not OsSEND1 has indispensable roles in resolving meiotic and DNA replication intermediates in rice male reproductive cells.…”

“…Two homologs of GEN1/Yen1 that are designated GEN1 and SEND1 exist across the plant kingdom (Olivier et al, 2016). It was reported that in Arabidopsis, AtSEND1 but not AtGEN1 acts as functional GEN1/Yen1 homolog.…”

“…It was reported that in Arabidopsis, AtSEND1 but not AtGEN1 acts as functional GEN1/Yen1 homolog. AtSEND1 plays important roles in repairing toxic replication intermediates and maintaining telomere homeostasis, but is not required for meiotic recombination (Olivier et al, 2016). OsSEND1 is induced by UV and DNA damage reagents, and consistently OsSEND1 plays a role in DNA repair in somatic cells (Furukawa et al, 2003).…”

“…There is only one Yen1/GEN1 type of resolvase in yeast, animals, and moss. On the contrary, two Yen1/ GEN1 homologs, named GEN1 and SINGLE-STRAND DNA ENDONUCLEASE1 (SEND1), exist in the genome of most plants (Bauknecht and Kobbe, 2014;Olivier et al, 2016). It was reported that in Arabidopsis, SEND1 but not GEN1 acts as a functional Yen1/GEN1 homolog and plays an important role in the repair of toxic replication intermediates and telomere homeostasis, but not in meiotic recombination (Olivier et al, 2016), suggesting a functional diversification of these two paralogs.…”

“…On the contrary, two Yen1/ GEN1 homologs, named GEN1 and SINGLE-STRAND DNA ENDONUCLEASE1 (SEND1), exist in the genome of most plants (Bauknecht and Kobbe, 2014;Olivier et al, 2016). It was reported that in Arabidopsis, SEND1 but not GEN1 acts as a functional Yen1/GEN1 homolog and plays an important role in the repair of toxic replication intermediates and telomere homeostasis, but not in meiotic recombination (Olivier et al, 2016), suggesting a functional diversification of these two paralogs. In rice, RNA interference-mediated gene silencing of rice GEN1 results in complete male sterility, which indicates that OsGEN1 plays an essential role in male microspore development in rice (Moritoh et al, 2005).…”