Non-homologous end-joining proteins are required for Agrobacterium T-DNA integration

Agrobacterium tumefaciens causes crown gall disease in dicotyledonous plants by introducing a segment of DNA (T‐DNA), derived from its tumour‐inducing (Ti) plasmid, into plant cells at infection sites. Besides these natural hosts, Agrobacterium can deliver the T‐DNA also to monocotyledonous plants, yeasts and fungi. The T‐DNA integrates randomly into one of the chromosomes of the eukaryotic host by an unknown process. Here, we have used the yeast Saccharomyces cerevisiae as a T‐DNA recipient to demonstrate that the non‐homologous end‐joining (NHEJ) proteins Yku70, Rad50, Mre11, Xrs2, Lig4 and Sir4 are required for the integration of T‐DNA into the host genome. We discovered a minor pathway for T‐DNA integration at the telomeric regions, which is still operational in the absence of Rad50, Mre11 or Xrs2, but not in the absence of Yku70. T‐DNA integration at the telomeric regions in the rad50 , mre11 and xrs2 mutants was accompanied by gross chromosomal rearrangements.