Deletion of TLS polymerases promotes homologous recombination in Arabidopsis

Unrepaired DNA damage hinders the maintenance of genome integrity because it blocks the catalytic activity of replicase. The stalled replication fork can be processed through either translesion synthesis (TLS) with specific polymerases, or replication using the undamaged template. To investigate how TLS activities are regulated and how the stalled replication fork is processed in plants, reversion frequencies and homologous recombination (HR) frequencies were analyzed using GUS-based substrates. The HR frequencies in plants deficient in DNA polymerase ζ (Pol ζ) or Rev1 were higher than that in wildtype plants under normal conditions, and were significantly increased by ultraviolet light irradiation. Heat shock protein (HSP) 90 is known to be involved in various stress responses. To examine the role of HSP90 in the regulation of damage tolerance, we analyzed reversion frequencies and HR frequencies in plants grown in the presence of a HSP inhibitor, geldanamycin (GDA). Reversion frequency was lower in GDA-treated plants than in mock-treated plants. Though the HR frequency was higher in GDA-treated wildtype plants than in mock-treated plants, no significant difference was detected in Rev1-deficient plants. In yeast, TLS polymerases interacted with each other or with a replication clump component, proliferating cell nuclear antigen (PCNA). HSP90 interacted with REV1 or REV7 in Nicotiana benthamiana cells. These results suggest that HSP90 interacts with TLS polymerase(s), which promotes error-prone TLS in plants.