Figure 1.

Model for the involvement of DNA polymerase θ in T-DNA integration. (A) Following generation of a double-strand DNA break (lightning bolt), the 5′ ends of plant DNA (green lines) are resected. Sequences within single-strand T-DNA molecules (T-strands, red lines), capped with VirD2 protein (blue oval) at their 5′ ends, align by microhomology with complementary regions of the exposed single-strand plant DNA. This can occur at both sides of the break (as pictured) or at one side only. (B) DNA polymerase θ (orange “pac-man” symbol) copies the T-strand sequence, using the exposed 3′ end of the plant DNA as a primer. The newly synthesized T-strand complementary sequence is ligated to the 5′ end of the break site, and the 5′ end of the T-strand is ligated to the 3′ end of the broken plant DNA following VirD2 removal. (C) Final result of integration of two T-DNA molecules in a head-to-head (RB-to-RB) orientation.