The plant DNA polymerase theta is essential for the repair of replication-associated DNA damage.

Safeguarding of genome integrity is a key process in all living organisms. Due to their sessile lifestyle, plants are particularly exposed to all kinds of stress conditions that could induce DNA damage. However, very few genes involved in the maintenance of genome integrity are indispensable to plants' viability. One remarkable exception is the POLQ gene, which encodes DNA polymerase theta (Pol θ), a non-replicative polymerase involved in trans-lesion synthesis during DNA replication and double-strand break (DSB) repair. The Arabidopsis tebichi (teb) mutants, deficient in Pol θ, have been reported to display severe developmental defects, leading to the conclusion that Pol θ is required for normal plant development. However, this essential role of Pol θ in plants is challenged by contradictory reports regarding the phenotypic defects of teb mutants and the recent finding that rice (Oryza sativa) null mutants develop normally. Here we show that the phenotype of teb mutants is highly variable. Taking advantage of hypomorphic mutants for the replicative DNA polymerase epsilon, which display constitutive replicative stress, we show that Pol θ allows maintenance of meristem activity when DNA replication is partially compromised. Furthermore, we found that the phenotype of Pol θ mutants can be aggravated by modifying their growth conditions, suggesting that environmental conditions impact the basal level of replicative stress and providing evidence for a link between plants' responses to adverse conditions and mechanisms involved in the maintenance of genome integrity.