The targeted deletion or alteration of genes relies on the integration of a DNA strand at a specific and predictable position into the genome of the host cell. This DNA strand must be engineered in such a way that both ends are identical to this specific gene locus. This is a prerequisite for being efficiently integrated via homologous recombination (HR). This is similar to the process used for creating knockout mice.
So far, this method of gene targeting in land plants has been carried out in the mosses Physcomitrella patens and Ceratodon purpureus, since in these non-seed plant species the efficiency of HR is several orders of magnitude higher than in seed plants.
Knockout mosses are stored at and distributed by a specialized biobank, the International Moss Stock Center.