Stephen F. Chandler

Genetic modification; the development of transgenic ornamental plant varieties

Plant transformation technology (hereafter abbreviated to GM, or genetic modification) has been used to develop many varieties of crop plants, but only a few varieties of ornamental plants. This disparity in the rate and extent of commercialisation, which has been noted for more than a decade, is not because there are no useful traits that can be engineered into ornamentals, is not due to market potential and is not due to a lack of research and development activity. The GM ornamental varieties which have been released commercially have been accepted in the marketplace. In this article, progress in the development of transgenic ornamentals is reviewed and traits useful to both consumers and producers are identified. In considering possible factors limiting the release of genetically modified ornamental products it is concluded that the most significant barrier to market is the difficulty of managing, and the high cost of obtaining, regulatory approval.

BIOTECHNOLOGY IN ORNAMENTAL HORTICULTURE

SummaryGenetic engineering techniques have so far had limited impact in the field of ornamental horticulture. As outlined in this review, transformation systems and potential genes of interest are available. As the development of new, novel varieties is an important driving force in the industry, there are, therefore, good prospects for the development of genetically modified ornamental variaties. The few products in the market to date may simply be a reflection of the relatively small scale of the industry compared to the major food crops, and the wide diversity of species within it. Commercial issues attendant to the use of gene technology in ornamental plants need careful consideration. These include careful choice of crop and background variety, the international regulatory process and freedom to operate.

Somatic embryogenesis in Eucalyptus globulus

Somatic embryos were obtained from 1% of cotyledon pieces and hypocotyls of mature embryos of Eucalyptus globulus Labill. cultured on media containing a high concentration of picloram or IBA. 2,4-D and other synthetic auxins did not yield somatic embryos or embryogenic callus. Somatic embryos arose indirectly via callus, being visible after four months, and directly, where little callus or adventitious root initiation occurred. Somatic embryos, formed directly from explants, were visible within five weeks. Various structural abnormalities of somatic embryos were observed, especially after induction on media containing picloram. Only two out of fifteen somatic embryos showed hypocotyl and radical elongation, but plantlets did not develop further.

Adventitious bud induction in Eucalyptus globulus Labill

SummaryAdventitious buds and shoots of Eucalyptus globulus Labill. (Tasmanian Bluegum) have been regenerated from cotyledons and hypocotyls from mature embryos and seedlings. Adventitious buds, were induced at high frequency with 0.05 μM thidiazuron in combination with 0.2 μM 2,4-dichlorophenoxyacetic acid or 5 μM α-naphthaleneacetic acid. Culture of explants in the dark inhibited bud induction, but up to 86% of cotyledons, longitudinally split just prior to culture, produced adventitious buds, in the light. Development of buds into shoots occurred only at low frequency, after transfer to media containing N6-benzylaminopurine.

Current status and biotechnological advances in genetic engineering of ornamental plants

Cut flower markets are developing in many countries as the international demand for cut flowers is rapidly growing. Developing new varieties with modified characteristics is an important aim in floriculture. Production of transgenic ornamental plants can shorten the time required in the conventional breeding of a cultivar. Biotechnology tools in combination with conventional breeding methods have been used by cut flower breeders to change flower color, plant architecture, post-harvest traits, and disease resistance. In this review, we describe advances in genetic engineering that have led to the development of new cut flower varieties.

Florigene Flowers: From Laboratory to Market

Plant biotechnology has opened up new ways for the production of crops with improved traits. It is also a useful tool for the breeding of flowers. The floriculture industry is driven by novelty. New varieties are most easily distinguished by new color but plant and flower form, variegation, fragrance, longevity, hardiness and resistance to insects and pests are also important.

Methods for genetic transformation in Dendrobium

Key messageThe genetic transformation ofDendrobiumorchids will allow for the introduction of novel colours, altered architecture and valuable traits such as abiotic and biotic stress tolerance.AbstractThe orchid genus Dendrobium contains species that have both ornamental value and medicinal importance. There is thus interest in producing cultivars that have increased resistance to pests, novel horticultural characteristics such as novel flower colours, improved productivity, longer flower spikes, or longer post-harvest shelf-life. Tissue culture is used to establish clonal plants while in vitro flowering allows for the production of flowers or floral parts within a sterile environment, expanding the selection of explants that can be used for tissue culture or genetic transformation. The latter is potentially the most effective, rapid and practical way to introduce new agronomic traits into Dendrobium. Most (69.4xa0%) Dendrobium genetic transformation studies have used particle bombardment (biolistics) while 64xa0% have employed some form of Agrobacterium-mediated transformation. A singe study has explored ovary injection, but no studies exist on floral dip transformation. While most of these studies have involved the use of selector or reporter genes, there are now a handful of studies that have introduced genes for horticulturally important traits.

Enhancement of Phosphate Absorption by Garden Plants by Genetic Engineering: A New Tool for Phytoremediation

Although phosphorus is an essential factor for proper plant growth in natural environments, an excess of phosphate in water sources causes serious pollution. In this paper we describe transgenic plants which hyperaccumulate inorganic phosphate (Pi) and which may be used to reduce environmental water pollution by phytoremediation. AtPHR1, a transcription factor for a key regulator of the Pi starvation response in Arabidopsis thaliana, was overexpressed in the ornamental garden plants Torenia, Petunia, and Verbena. The transgenic plants showed hyperaccumulation of Pi in leaves and accelerated Pi absorption rates from hydroponic solutions. Large-scale hydroponic experiments indicated that the enhanced ability to absorb Pi in transgenic torenia (AtPHR1) was comparable to water hyacinth a plant that though is used for phytoremediation causes overgrowth problems.

Expression of flavonoid 3',5'-hydroxylase and acetolactate synthase genes in transgenic carnation: assessing the safety of a nonfood plant.

For 16 years, genetically modified flowers of carnation ( Dianthus caryophyllus ) have been sold to the floristry industry. The transgenic carnation carries a herbicide tolerance gene (a mutant gene encoding acetolactate synthase (ALS)) and has been modified to produce delphinidin-based anthocyanins in flowers, which conventionally bred carnation cannot produce. The modified flower color has been achieved by introduction of a gene encoding flavonoid 3,5-hydroxylase (F35H). Transgenic carnation flowers are produced in South America and are primarily distributed to North America, Europe, and Japan. Although a nonfood crop, the release of the genetically modified carnation varieties required an environmental risk impact assessment and an assessment of the potential for any increased risk of harm to human or animal health compared to conventionally bred carnation. The results of the health safety assessment and the experimental studies that accompanied them are described in this review. The conclusion from the assessments has been that the release of genetically modified carnation varieties which express F35H and ALS genes and which accumulate delphinidin-based anthocyanins do not pose an increased risk of harm to human or animal health.

Flower Color and Its Engineering by Genetic Modification

Flower color is mainly determined by the constituent profile of the chemicals flavonoids and the colored subclass of those compounds, the anthocyanins. Flowers often contain specific flavonoids, and thus limited flower colors are available within a species due to genetic constraints. Engineering the flavonoid biosynthetic pathway by expressing a heterologous gene has made it possible to obtain color varieties that cannot be achieved within a species by hybridization or mutational breeding. General tactics for successful engineering flower color have been established on the basis of engineering results obtained in model species such as petunia and torenia. Highly efficient expression of a heterologous gene(s) can be achieved by an optimal combination of promoter, translational enhancer, coding region sequence, and terminator. In addition to expression of heterologous gene, downregulation of competing pathways and/or using color biosynthesis mutant hosts is necessary. As well as a suitable genetic background, it is also important to select hosts with a high market position and value. An efficient transformation system for each target species has to be established. Technical skills and enough finance are also necessary to obtain permits to commercialize genetically modified plants. Violet carnations, roses, and chrysanthemums have been developed by expressing a petunia, pansy, or campanula flavonoid 3′,5′-hydroxylase gene, and genetically modified carnation and rose varieties have been commercialized. Expression of the anthocyanin 3′,5′-glucosyltransferase gene in chrysanthemum in addition to flavonoid 3′,5′-hydroxylase resulted in production of pure blue flower color due to a copigmentation effect with endogenous flavones. Orange petunia expressing maize dihydroflavonol 4-reductase gene and accumulating non-native pelargonidin have been grown worldwide. Though this has been from a non-intentional release of a genetically modified organism, the case provides a good example to show that a combination of genetic engineering and hybridization breeding can produce commercially highly sought after cultivars.