Search

The formation of a new species can occur by an asexual mechanism by transfer of entire nuclear genomes between plant cells as shown by the creation of a new allopolyploid plant from parental herbaceous and woody plant species, this mechanism is a potential new tool for crop improvement. Speciation by growing together Grafting is a common occurrence in nature and is familiar as a means of manipulating plants and trees for use in agriculture and horticulture. Here Ralph Bock and colleagues demonstrate that entire nuclear genomes can be transferred across the graft junction from plant to plant. In grafting experiments between the tree tobacco Nicotiana glauca and the cigarette tobacco N. tabacum (woody and herbaceous species, respectively), horizontal transfer of nuclear genomes can result in the formation of a new polyploid species -- Nicotiana tabauca. This is an example of allopolyploidization, the combination of the genomes from two different species that has contributed to evolutionary innovation, adaptation, speciation and domestication. It is thought to occur through hybridization events between species, accompanied or followed by genome duplication, but this work shows that it can also occur through an asexual mechanism that is readily available as a potential tool for crop improvement. Allopolyploidization, the combination of the genomes from two different species, has been a major source of evolutionary innovation and a driver of speciation and environmental adaptation.sup.1,2,3,4. In plants, it has also contributed greatly to crop domestication, as the superior properties of many modern crop plants were conferred by ancient allopolyploidization events.sup.5,6. It is generally thought that allopolyploidization occurred through hybridization events between species, accompanied or followed by genome duplication.sup.6,7. Although many allopolyploids arose from closely related species (congeners), there are also allopolyploid species that were formed from more distantly related progenitor species belonging to different genera or even different tribes.sup.8. Here we have examined the possibility that allopolyploidization can also occur by asexual mechanisms. We show that upon grafting--a mechanism of plant-plant interaction that is widespread in nature--entire nuclear genomes can be transferred between plant cells. We provide direct evidence for this process resulting in speciation by creating a new allopolyploid plant species from a herbaceous species and a woody species in the nightshade family. The new species is fertile and produces fertile progeny. Our data highlight natural grafting as a potential asexual mechanism of speciation and also provide a method for the generation of novel allopolyploid crop species., Author(s): Ignacia Fuentes [sup.1] , Sandra Stegemann [sup.1] , Hieronim Golczyk [sup.2] , Daniel Karcher [sup.1] , Ralph Bock [sup.1] Author Affiliations: (1) Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, [...]

Plastids (chloroplasts) are maternally inherited in most crops. Maternal inheritance excludes plastid genes and transgenes from pollen transmission. Therefore, plastid transformation is considered a superb tool for ensuring transgene containment and improving the biosafety of transgenic plants. Here, we have assessed the strictness of maternal inheritance and the extent to which plastid transformation technology confers an increase in transgene confinement. We describe an experimental system facilitating stringent selection for occasional paternal plastid transmission. In a large screen, we detected low-level paternal inheritance of transgenic plastids in tobacco. Whereas the frequency of transmission into the cotyledons of [F.sub.1] seedlings was [approximately equal to] 1.58 x [10.sup.-5] (on 100% cross-fertilization), transmission into the shoot apical meristem was significantly lower (2.86 x [10.sup.-6]). Our data demonstrate that plastid transformation provides an effective tool to increase the biosafety of transgenic plants. However, in cases where pollen transmission must be prevented altogether, stacking with other containment methods will be necessary to eliminate the residual outcrossing risk. biosafety | Nicotiana tabacum | plastid transformation | pollen transmission | paternal leakage

The high-value carotenoid astaxanthin (3,3'-dihydroxy-β,β-carotene-4,4'-dione) is one of the most potent antioxidants in nature. In addition to its large-scale use in fish farming, the pigment has applications as a food supplement and an active ingredient in cosmetics and in pharmaceuticals for the treatment of diseases linked to reactive oxygen species. The biochemical pathway for astaxanthin synthesis has been introduced into seed plants, which do not naturally synthesize this pigment, by nuclear and plastid engineering. The highest accumulation rates have been achieved in transplastomic plants, but massive production of astaxanthin has resulted in severe growth retardation. What limits astaxanthin accumulation levels and what causes the mutant phenotype is unknown. Here, we addressed these questions by making astaxanthin synthesis in tobacco (Nicotiana tabacum) plastids inducible by a synthetic riboswitch. We show that, already in the uninduced state, astaxanthin accumulates to similarly high levels as in transplastomic plants expressing the pathway constitutively. Importantly, the inducible plants displayed wild-type-like growth properties and riboswitch induction resulted in a further increase in astaxanthin accumulation. Our data suggest that the mutant phenotype associated with constitutive astaxanthin synthesis is due to massive metabolite turnover, and indicate that astaxanthin accumulation is limited by the sequestration capacity of the plastid. [ABSTRACT FROM AUTHOR]