Surprises for Agrobacterium T-DNA integration into host genomes
Agrobacterium species transfer DNA (T-DNA) to host plants, a unique example of interkingdom horizontal gene transfer. Once inside the nucleus, T-DNA integrates into the host genome. The mechanism of integration has been widely debated, but the current favored hypothesis is that double-strand T-DNA molecules link to double-strand DNA break sites in plant chromosomes using the host's non-homologous end-joining (NHEJ) machinery. It was thus thought that if one were to mutate genes encoding NHEJ proteins, T-DNA integration and, thus, transformation would decrease. We mutated numerous genes in the Arabidopsis NHEJ pathways (both "classical" and "backup" pathways). Surprisingly, in no instance did we see decreased transformation. Rather, in some instances we saw INCREASED transformation and T-DNA integration. Simultaneous mutation of NHEJ genes in both the classical and backup pathways also had no effect on transformation or T-DNA integration, indicating that some other yet unknown pathway for T-DNA integration must exist. We explain the surprising observation that mutation of NHEJ genes can increase transformation by a new model: Mutation of NHEJ genes slows host double-strand DNA break repair, providing increased opportunity for T-DNA integration.
Park, S.-Y., Vaghchhipawala, Z., Vasudevan, B., Lee, L.-Y., Shen, Y., Singer, K., Waterworth, W.M., Zhang, Z., West, C.E., Mysore, K.S, and Gelvin, S.B. 2015. Agrobacterium T-DNA integration into the plant genome can occur without the activity of key non-homologous end-joining proteins. Plant J. DOI: 10.1111/tpj.12779.
Photo and article submitted by Stanton B. Gelvin, Edwin Umbarger Distinguished Professor of Biological Sciences.