Engineering the plastid genome of Nicotiana sylvestris, a diploid model species for plastid genetics.
Methods in Molecular Biology. 701:37-50. Abstract
The plastids of higher plants have their own approximately 120-160-kb genome that is present in 1,000-10,000 copies per cell. Engineering of the plastid genome (ptDNA) is based on homologous recombination between the plastid genome and cloned ptDNA sequences in the vector. A uniform population of engineered ptDNA is obtained by selection for marker genes encoded in the vectors. Manipulations of ptDNA include (1) insertion of transgenes in intergenic regions; (2) posttransformation excision of marker genes to obtain marker-free plants; (3) gene knockouts and gene knockdowns, and (4) cotransformation with multiple plasmids to introduce nonselected genes without physical linkage to marker genes. Most experiments on plastome engineering have been carried out in the allotetraploid Nicotiana tabacum. We report here for the first time plastid transformation in Nicotiana sylvestris, a diploid ornamental species. We demonstrate that the protocols and vectors developed for plastid transformation in N. tabacum are directly applicable to N. sylvestris with the advantage that the N. sylvestris transplastomic lines are suitable for mutant screens.
Plastid transformation in flowering plants.
Genomics of Chloroplasts and Mitochondria. 35:393-414. Abstract
The plastid genome of higher plants is relatively small, 120–230-kb in size, and present in up to 10,000 copies per cell. Standard protocols for the introduction of transforming DNA employ biolistic DNA delivery or polyethylene glycol treatment. Genetically stable, transgenic plants are obtained by modification of the plastid genome by homologous recombination, followed by selection for the transformed genome copy by the expression of marker genes that protect the cells from selective agents. Commonly used selective agents are antibiotics, including spectinomycin, streptomycin, kanamycin and chloramphenicol. Selection for resistance to amino acid analogues has also been successful. The types of plastid genome manipulations include gene deletion, gene insertion, and gene replacement, facilitated by specially designed transformation vectors. Methods are also available for post-transformation removal of marker genes. The model species for plastid genetic manipulation is Nicotiana tabacum, in which most protocols have been tested. Plastid transformation is also available in several solanaceous crops (tomato, potato, eggplant) and ornamental species (petunia, Nicotianasylvestris). Significant progress has been made with Brasssicaceae including cabbage, oilseed rape and Arabidopsis. Recent additions to the crops in which plastid transformation is reproducibly obtained are lettuce, soybean and sugar beet. The monocots are a taxonomic group recalcitrant to plastid transformation; initial inroads have been made only in rice.
Plastid transformation in Nicotiana tabacum and Nicotiana sylvestris by biolistic DNA delivery to leaves.
Chloroplast Biotechnology: Methods and Protocols. 1132:147-163. Abstract
The protocol we report here is based on biolistic delivery of the transforming DNA to tobacco leaves, selection of transplastomic clones by spectinomycin resistance and regeneration of plants with uniformly transformed plastid genomes. Because the plastid genome of Nicotiana tabacum derives from Nicotiana sylvestris, and the two genomes are highly conserved, vectors developed for N. tabacum can be used in N. sylvestris. Also, the tissue culture responses of N. tabacum cv. Petit Havana and N. sylvestris accession TW137 are similar, allowing plastid engineering protocols developed for N. tabacum to be directly applied to N. sylvestris. However, the tissue culture protocol is applicable only in a subset of N. tabacum cultivars. Here we highlight differences between the protocols for the two species. We describe updated vectors targeting insertions in the unique and repeated regions of the plastid genome as well as systems for marker excision. The simpler genetics of the diploid N. sylvestris, as opposed to the allotetraploid N. tabacum, make it an attractive model for plastid transformation.