By Pecinka Ales and Eva Dvořák Tomaštíková
Background: Cellular DNA is constantly damaged by various internal and external factors that eventually lead to mutations, reduced growth or even death. To ensure genome stability, organisms have evolved sophisticated and intricate DNA repair systems. We understand how cells remove some types of DNA damage, but the mechanisms of detoxification from other types of damage remain poorly characterized. For example, DNA-protein crosslinks, i.e. proteins covalently attached to DNA molecule, hinder the essential processes of replication and transcription.
Question: Our aim is to identify molecular factors protecting plants from toxic DNA-protein crosslinks. We set up a forward-directed genetic screen to identify mutants hypersensitive to the cytidine analog zebularine, which crosslinks DNA METHYLTRANSFERASE1 (MET1) protein to the 45S rDNA repeats, and characterized the first candidate.
Findings: We mapped HYPERSENSITIVE TO ZEBULARINE 1 (HZE1) candidate as SMC6B, a core component of the Structural maintenance of chromosomes 5/6 (SMC5/6) complex. HZE1 plays a key role in DNA protein crosslink repair as it is needed for the repair of different classes of crosslinks. We also showed that the SMC5/6 complex acts in parallel with the known proteolytic and nucleolytic DNA-protein crosslink repair pathways. To shed light on the possible mechanism of SMC5/6 action, we focused on the Small ubiquitin modifier (SUMO) ligation activity of this complex. We showed the SMC5/6 complex–dependent accumulation of SUMO at the crosslinked foci induced by zebularine.
Next steps: We will focus further on the role of SUMO in plant DNA damage repair and will characterize other HZE candidates coming from the forward-directed genetic screen. This will help us understand the mechanisms of DNA-protein crosslink repair in plants.
Eva Dvořák Tomaštíková, Klara Prochazkova, Fen Yang, Jitka Jemelkova, Andreas Finke, Annika Dorn, Mahmoud Said, Holger Puchta, Ales Pecinka. (2023). SMC5/6 complex-mediated SUMOylation stimulates DNA-protein crosslink repair in Arabidopsis. https://doi.org/10.1093/plcell/koad020