Agrobacterium tumefaciens can genetically transform eukaryotic cells, In many bacteria, pill are required for interbacterial DNA transfer. The formation of pill by Agrobacterium required induction of tumor-inducing (Ti) plasmid-encoded virulence genes and growth at low temperature, Agenetic analysis demonstrated that virA, virG, virB1 through virB11, and virD4 are the only Ti plasmid genes necessary for pilus assembly, The loss and gain of pill in various mutants correlated with the loss and gain of transferred DNA (T-DNA) transfer functions, which is consistent with the view that Agrobacterium pill are required for transfer of DNA to plant cells in a process similar to that of conjugation.