The invention provides methods and compositions for increasing the efficiency of genetic transformation of host cells, including plant cells, and other eukaryotic cells, by reducing the expression of a polypeptide active in a pathway, such as the NHEJ pathway, for repairing damage to the cellular genome. In certain embodiments, the polypeptide is active in repairing double strand breaks (DSB's) of a cellular genome, and may include XRCC4, KU70, KU80, the DNA-activated Protein Kinase (DNA-Pkcs), and ATM. Methods for enhancing the resistance of plant cells to Crown Gall disease are also provided. In another aspect, genetic regulatory elements are provided, including an XRCC4 promoter.