Prerequisite to the development of a transformation system is the preparation of propagules from a cell line in sufficient numbers and with acquired competence for uptake of the added DNA and, ultimately, for efficient phenotypic expression of some rare transforming event. Also important in the development of a transformation system is the design of the vector or added DNA so as to contain at least one selectable marker gene for recognition and recovery of this rare transforming event, The introduced gene(s) that are targeted for expression by transformants should be bracketed with control signals appropriate to the cell line under investigation.
Regenerative protoplasts or cell wall-less propagules, derived experimentally from either intact fungal cells or their mitotic spore states, are commonly employed in the development of fungal transformation systems. Moreover, vectors for such experiments are generally designed for integrative, rather than replicative, transformation. These vectors often exhibit a wide latitude for heterologous gene expression (Fincham, 1989; Timberlake and Marshall, 1989).
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