The competent host is essential for transformation with recombinant DNA. Many kinds of host cells, including E.coli, yeat ,animal, and plant cell, are available for genetic engineering. DNA is a hydrophilic molecule; it cannot be made capable of taking up DNA . This is done by treating them with a specific concentration of a divalent cation, such as calcium ion.
In eukaryotes, transformation is replaced by the term transfection.
Possible methods-

Competent host