Control of seed germination in transgenic plants based on the segregation of a two-component genetic system

Abstract

We have developed a repressible seed-lethal (SL) system aimed at reducing the probability of transgene introgression into a population of sexually compatible plants. To evaluate the potential of this method, tobacco plants were transformed with an SL construct comprising gene 1 and gene 2 from Agrobacterium tumefaciens whereby gene 1 was controlled by the seed-specific phaseolin promoter modified to contain a binding site for the Escherichia coli TET repressor (R). The expression of this construct allows normal plant and seed development but inhibits seed germination. Plants containing the SL construct were crossed with plants containing the tet R gene to derive plant lines where the expression of the SL construct is repressed. Plant lines that contained both constructs allowed normal seed formation and germination, whereas seeds in which the SL construct was separated from the R gene through segregation did not germinate. The requirements of such a method to efficiently control the flow of novel traits among sexually compatible plants are discussed.O ne of the major concerns surrounding the widespread use of genetically modified crops is that these crops may transmit their novel traits to wild relatives or that novel traits may contaminate other related crop species. This is of particular concern for crops where seed is saved, because seed formed by cross-pollination from varieties carrying novel genes can lead to populations where the novel gene becomes established. Thus, a mechanism to reduce the incidence of the transfer of novel traits to the seed of wild or domestic relatives can provide a means of restricting the novel traits to the specific variety being cultivated. Examples of current containment techniques include maternal inheritance, male sterility, seed sterility, cleistogamy, apomixis, incompatible genomes, and transgenic mitigation by temporal or tissue-specific control of suicide genes (reviewed in ref. 1).In this article, we describe an approach to gene containment that relies on the maintenance of a seed-lethal (SL) gene (which can be linked to a novel trait) and a repressor (R) element added by crossing. The rationale of the method is to achieve repression of seed lethality by combining the SL construct with the R construct. The combination of the two elements leads to repression of the SL gene, thus allowing seed propagation of the plant by selfing. However, pollen-mediated incrossing or outcrossing can result in the separation of the two elements, in which case the SL construct is consequently activated in the seed embryo, causing the arrest of germination for seed containing the SL construct and the linked novel trait (Fig. 1). Under optimized conditions (single SL and R loci at the same location on both parental chromosomes) such a method would be simple and efficient and would not require any intervention under managed conditions.In the example presented, seed lethality is achieved by the embryo-specific overproduction of auxin mediated by the products of Agrobacterium tumefaciens gene 1,...

Poor competitive fitness of transgenically mitigated tobacco in competition with the wild type in a replacement series

“…Two general approaches are proposed to deal with the problems of transgene flow and establishment: containment of the transgenes within the transgenic crop (Oliver et al 1998;Daniell 2002;Jepson 2002;Schernthaner et al 2003;Kuvshinov et al 2004;Maliga 2004), and transgenic mitigation (TM) (Gressel 1999;Al-Ahmad et al 2004) of the effects of the primary transgenic trait should it escape and move to an undesired target. While most containment mechanisms, if they work at all, will severely restrict gene flow in one direction, and most cannot contain gene flow in both directions.…”

Risk mitigation of genetically modified bacteria and plants designed for bioremediation

“…A somewhat similar technique also uses genetic control of seed sterility but has a different outcome in that the seeds only become sterile upon outcrossing to other plants [69]. Seed sterility is achieved by using two genes (iaaM and iaaH), from the Ti plasmid of Agrobacterium tumefaciens, that encode the enzymes for the production of the plant hormone indole-3-acetic acid, expression of which permits normal plant and seed development but inhibits seed germination.…”

Impact environnemental des cultures transgéniques

“…La transformation du génome chloroplastique représente, par exemple, une alternative aux procédés de transformation nucléaire pour assurer l'absence de transgènes dans le pollen des espèces végétales montrant une hérédité chloroplastique maternelle stricte (Daniell 2002). Des lignées transgéniques à stérilité mâle cultivées à proximité de lignées conventionnelles fertiles assurant une disponibilité en pollen sexuellement fonctionnel pourraient aussi se montrer utiles chez plusieurs espèces (Feil et al 2003;Schernthaner et al 2003). De même, des stratégies de confinement reposant sur la stérilité ou un développement compromis des semences pourraient susciter de l'intérêt sur le plan environnemental (Koivu et al 2001;Odell et al 1994;Tomes 1997), malgré les controverses entourant au départ ce type de technologie (Visser et al 2001).…”