Transformation of Pollen

Abstract

In most transformation systems today, in vitro regeneration of plants is an essential step and very often the main limiting factor for yield and success. Circumvention of in vitro regeneration would therefore be highly advantageous. The simplest way to do this would be to transfer DNA into the gametes and, after gamete fusion, to exploit seed embryogenesis for plant formation. If feasable, such an approach would be technically simpler and faster than methods based on in vitro regeneration. It should also be universal in its application. In addition, one would avoid the problem of somaclonal variation resulting from in vitro regeneration. Somaclonal variation in transgenic commercial lines of crop plants can spoil the advantage obtained by transferring a transgene. The problem of chimaera that is intrinsic to in vitro regeneration, would also be avoided. Gametes in the strict sense are not easily accessible in plants although progress has been achieved in isolating both sperm and egg cells (1). Both, male as well as female gametes, can be used for gene transfer. The main advantage of the egg cell might be the efficient formation of a whole plant either in situ or after isolation and in vitro culture. The latter remains to be shown, however. The male gamete in higher plants is not a free, mobile cell as in lower plants or in animals, but is part of a larger structure, the pollen. And only the pollen as such is able to perform fertilization in situ, while the isolated sperm cell would have to be fused in vitro with the egg cell. Attempts to use male gametes for gene transfer have therefore concentrated on the transfer through pollen.