Effect of chromatin upon Agrobacterium T-DNA integration and transgene expression

Agrobacterium tumefaciens transfers DNA (T-DNA) to plant cells, where it integrates into the plant genome. Little is known about how T-DNA chooses sites within the plant chromosome for integration. Previous studies indicated that T-DNA preferentially integrates into transcriptionally active regions of the genome, especially in 5'-promoter regions. This would make sense, considering that chromatin structure surrounding active promoters may be more "open" and accessible to foreign DNA. However, recent results suggest that this seemingly non-random pattern of integration may be an artifact of selection bias, and that T-DNA may integrate more randomly than previously thought. In this chapter, I discuss the history of these observations and the role chromatin proteins may play in T-DNA integration and transgene expression. Understanding how chromatin conformation may influence T-DNA integration will be important in developing strategies for reproducible and stable transgene expression, and for gene targeting.