Cisgenesis strongly improves introgression breeding and induced translocation breeding of plants Evert Jacobsen 1, 3 and Henk J. Schouten 2 1 Wageningen University and Research Centre, Laboratory of Plant Breeding, P.O. Box 386, 6700 AJ Wageningen, The Netherlands 2 Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands 3 Transforum Agribusiness & Rural Areas, Louis Pasteurlaan 6, 2700 AB Zoetermeer, The Netherlands There are two ways for genetic improvement in classical plant breeding: crossing and mutation. Plant varieties can also be improved through genetic modification; however, the present GMO regulations are based on risk assessments with the transgenes coming from non-crossable species. Nowadays, DNA sequence infor- mation of crop plants facilitates the isolation of cisgenes, which are genes from crop plants themselves or from crossable species. The increasing number of these iso- lated genes, and the development of transformation protocols that do not leave marker genes behind, pro- vide an opportunity to improve plant breeding while remaining within the gene pool of the classical breeder. Compared with induced translocation and introgression breeding, cisgenesis is an improvement for gene transfer from crossable plants: it is a one-step gene transfer without linkage drag of other genes, whereas induced translocation and introgression breeding are multiple step gene transfer methods with linkage drag. The sim- ilarity of the genes used in cisgenesis compared with classical breeding is a compelling argument to treat cisgenic plants as classically bred plants. In the case of the classical breeding method induced translocation breeding, the insertion site of the genes is a priori unknown, as it is in cisgenesis. This provides another argument to treat cisgenic plants as classically bred plants, by exempting cisgenesis of plants from the GMO legislations. Developments in classical and modern plant breeding At the onset of plant breeding, sufficient genetic variation was available, and the breeder did not need many crosses, seedlings or selection schemes to obtain new varieties that were more domesticated than the existing ones. However, the occurrence of (a)biotic stress and the need for quality traits, requires more genetic variation and stimulated mutation breeding for the direct improvement of existing varieties, or for crosses with wild species and consecutive backcrosses, for improved breeding material containing novel traits. This, more complex, breeding approach with wild species, called introgression breeding, has been worked out in detail for many crops [1], and there are many successful examples of the domestication of genes coding for new traits [2]. In some important interspecific crosses, suppression of recombination occurred, and this required induced translocations by induction of mutations; this was followed by backcrosses [2,3]. Biotechnology has broadened these approaches by adding in vitro techniques, such as embryo rescue, regen- eration and protoplast fusion; genomics – for the develop- ment of genetic maps with molecular markers, enabling marker assisted selection (MAS) and comparative geno- mics [1,4]; and genetic modification (GM). Therefore, existing varieties can also be improved by genetic modification using transgenes and, more recently, cisgenes originating from the crop plant itself or from cross- able species [5,6]. Worldwide, strict rules accompany the GM approach; these are primarily based on transgenes representing the new gene pool. However, isolated cisgenes from the gene pool of the classical breeder are increasingly becoming available, in combination with marker-free trans- formation protocols. Therefore, we argue that the risks of cisgenes are comparable with those in classical breeding, and comparisons with classical breeding approaches have been made to classify cisgenesis and transgenesis (Box 1). Mutation breeding Mutations are the ultimate source of genetic variation, and together with selection and genetic recombination, the most important factors in evolution. Mutations at the gene level are mostly recessive and, by definition, single-cell events; therefore, they are always accompanied with chimerism. This problem, and that of making recessive mutations homozygous, can be solved in seed propagated crops through the sexual cycle, but this is not possible in heterozygous, vegetatively propagated crops [7]. Therefore, in the auto- tetraploid potato, for example, only a few mutations (tuber color, tuber shape and amylose-free starch) have been used for breeding purposes [7]. However, in diploid apple the occurrence of spontaneous mutations leading to improved cultivars are frequently found, as shown in the skin color- and growth rate-altered mutants of the cultivars Golden Delicious, Jonagold and Elstar [8]. Many seed propagated crops with homozygous parents, such as barley, rice, tomato, Review TRENDS in Biotechnology Vol.25 No.5 Corresponding author: Jacobsen, E. (evert.jacobsen@wur.nl). Available online 23 March 2007. www.sciencedirect.com 0167-7799/$ – see front matter ß 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tibtech.2007.03.008