144 Novel approach in plastid transformation Aart JE van Bel*†, Julian Hibberd‡, Dirk Prüfer§ and Michael Knoblauch* Engineering the nuclear genome of plants is perceived to be dispersal of crop plants engineered for herbicide resistance associated with problems regarding biosafety and the stability may render their weedy relatives insensitive to certain her- of expression of the transgene. Alternative transformation bicides [2]; transgenic pollen may be toxic to nontarget strategies using the genomic outfit of the plastid promise to insects such as butterflies [3••]. be more successful in this respect. Over the past few years progress has been made in screening procedures, and plastid The introduction of genes by engineering the chloroplast transformation technology has allowed function to be assigned has been proposed to remedy the problems associated with to open reading frames, massive expression of insecticidal transgene dispersal into the wild plant population. As there agents and proteins involved in herbicide resistance, and the are no plastids, and hence plastid DNA, in the pollen of accumulation of biopolymers. Recently, the design of a novel most crops (exceptions being alfalfa and possibly rice and femtoinjection technique that allows injection into chloroplasts pea; see [4–6]), any gene introduced into chloroplast-engi- has provided the opportunity to further manipulate and under- neered plants is unlikely to be transferred via the pollen to stand chloroplastic gene expression. the next generation. Introgression of genes from wild rela- tives, however, could eventually allow chloroplast trans- Addresses genes to invade the nontransformed population. The *Institute for General Botany and Plant Physiology, Justus Liebig extent to which introgression of genes between wild rela- University, Senckenbergstrasse 17, D-35390 Giessen, Germany tives occurs is at present uncertain, although in general † e-mail:
[email protected] introgression is unusual [7••].