GM Crop Database

Database Product Description

66
Host Organism
Dianthus caryophyllus (Carnation)
Trait
Increased shelf-life due to reduced ethylene accumulation through introduction of truncated aminocyclopropane cyclase (ACC) synthase gene; Sulfonylurea herbicide tolerance, specifically triasulfuron and metsulfuron-methyl.
Trait Introduction
Agrobacterium tumefaciens-mediated plant transformation.
Proposed Use

Production for the cut-flower industry.

Product Developer
Florigene Pty Ltd.

Summary of Regulatory Approvals

Country Food Feed Environment Notes
Australia 1995
European Union 1998

Introduction Expand

Harvested carnation (Dianthus caryophyllus L.) flowers have a defined 'vase life', or time for which the flowers will stay fresh prior to beginning to shrink, dry out and die. This senescence process is triggered by production of a natural plant hormone, ethylene, by the flower. Flower death can also be triggered by exposure of flowers to external sources of ethylene, such as fruit and exhaust fumes. Typically, flower growers have controlled wilting by treating flowers with chemicals (e.g. silver thiosulfate) that either inhibit ethylene synthesis in the flower, or prevent the flower from responding to ethylene.

The enzyme 1-aminocyclopropane-1-carboxyllic acid (ACC) synthase, normally found in carnations, is responsible for the conversion of s-adenosylmethionine to ACC, which is the immediate precursor of ethylene. The transgenic carnation line 66 was developed using recombinant DNA techniques to display suppressed ACC synthase activity, and thus reduced ethylene synthesis and therefore longer vase life, by inserting an additional truncated copy of the ACC synthase encoding gene. The presence of the truncated ACC synthase gene suppresses the normal expression of the native ACC synthase gene, and while not completely understood, the mechanism of “downregulation” is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated ACC synthase gene.

An additional gene encoding a variant form of the enzyme acetolactate synthase (ALS) was also introduced into this transgenic carnation line in order to confer the trait of tolerance to sulfonylurea type herbicides (e.g., chlorsulfuron, commonly known as Glean™), which are potent inhibitors of ALS. Acetolactate synthase (also known as acetohydroxy acid synthase; AHAS) is involved in the conversion of threonine to alpha-aceto-alpha-hydroxybutyrate and pyruvate to alpha-acetolactate, which are key precursors in the biosynthesis of the essential branched chain amino acids isoleucine and valine, respectively. Alpha-acetolactate is also a precursor in the synthesis of leucine. The variant form of ALS introduced into this carnation line was isolated from a chlorsulfuron tolerant tobacco (Nicotiana tabacum). This trait was introduced as a means of selecting for transformed plants during tissue culture regeneration as sulfonylurea herbicides are not, and will not be, used in the carnation industry.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
ACC 1-aminocyclopropane-1-carboxylate synthase DR

CaMV 35S

A. tumefaciens nopaline synthase (nos) 3'-untranslated region

Truncated, sense orientation

surB acetolactate synthase HT CaMV 35S surB terminator from N. tabacum

Characteristics of Dianthus caryophyllus (Carnation) Expand

Center of Origin Reproduction Toxins Allergenicity

The species is native to the Mediterranean region, including Europe, Asia, and northern Africa.

Carnation flowers are pollinated primarily by butterflies and sometimes by other insects.

The parts of the carnation plants are not thought to be toxic, and the flowers are considered edible.

Occupational exposure to carnation flowers has been associated with allergic reactions in humans.

Modification Method Expand

Transgenic carnation line 66 was produced by Agrobacterium-mediated transformation of carnation plants (Dianthus caryophyllus L., cultivar Ashley) in which the transfer-DNA (T-DNA) region of the bacterial Ti plasmid was modified to contain a truncated copy of the ACC synthase encoding gene and the ALS encoding gene (surB) from a chlorsulfuron tolerant isolate of tobacco. The truncated ACC synthase gene was arranged in the “sense” orientation and contained promoter sequences from the 35S transcript of cauliflower mosaic virus (CaMV) and transcription termination and a 3’ polyadenylation signal sequence from the 3’ untranslated region of the A. tumefaciens nopaline synthase gene (3’ nos).

The surB gene was used as a selectable marker to identify transformed plants during tissue culture regeneration. Expression of the ALS enzyme was regulated using the CaMV 35S promoter and the surB terminator derived from tobacco (Nicotiana tabacum).

Characteristics of the Modification Expand

Genetic Stability of the Introduced Trait

The ACC synthase gene and the surB marker gene were stably integrated into the transgenic carnation line 66. Line 66 was reproduced through vegetative reproduction, as were its progeny, as well as progeny derived through crosses with traditionally bred non-genetically modified carnation plants.

Environmental Safety Considerations Expand

Field Trials

Carnation line 66 and derived lines have been tested in trials in the United States, the United Kingdom, the Netherlands, and Australia. Results demonstrated that genetically modified carnations had a vase-life in water of 22 days, without requiring chemical treatment with STS or AOA. In the same study, non-genetically modified carnations only had a vase-life in water of 10 days, and required treatment with STS or AOA to guarantee a vase-life in water of at least 8 days.

Outcrossing

The commercial standard carnation varieties are generally male sterile and rarely produce anthers. In the case of fertile flowers, little pollen is produced, which can only be transferred by insects. In commercial carnation production, outcrossing is unlikely as flowers are cut before opening. Should flowers open, only certain insects can access nectaries in flowers and there are very few opportunities for this to occur during transit and sale. Furthermore, carnations plants require 6 weeks for seed development. A genetically modified cut carnation flower lasts only 3-4 weeks, which is not enough time for seed set.

Many Dianthus species occur as common wildflowers. There has never been any evidence of hybridization between carnation and these species, nor after decades of cultivation have carnations been found in the wild. The biology of carnation is such that there are no realistic ways for the genetically modified plants to escape from cultivation and become established as populations in the wild, or for gene dispersal from the genetically modified carnation to occur.

Weediness Potential

Genetically modified carnation line 66 and derived lines have little potential to become weeds. After decades of cultivation, carnations have never been found in the wild. Carnation has no weedy characteristics and is not closely related to known weeds.

Impact on Biodiversity

The risk of transferring genetic traits from transgenic carnation line 66 to species in unmanaged environments was not judged to be significant. The genetically modified carnation line 66 is intended for cultivation by cut flower growers, flower auctions, flower wholesalers, retailers and breeders. Plants are sold as flowers, cuttings or whole plants.

Abstract Collapse

Carnations (Dianthus carophyllus L.) are among the most extensively grown cut flowers with more than 10 billion carnations produced around the world each year. Carnations are cultivated by growers, flower auctions, flower wholesalers, retailers and plant breeders worldwide.

Carnations are sold to consumers as cut flowers, but are also sold as cuttings or plants. Flowers are cut with great care to ensure that the consumer receives a flower that will last as long as possible. However, once a flower has been cut, it starts to deteriorate and is susceptible to premature inrolling (wilting) of the petals. The deterioration is a serious problem for carnations and is caused by the plants own production of ethylene, a natural plant hormone that triggers the aging process and leads to petal wilting. To ensure that the flowers have an acceptable vase-life, growers chemically treat all carnations with a solution of silver thiosulfate (STS) or other chemicals such as amino-oxyacetic acid (AOA). These chemicals can double the usual vase-life by reducing the plant's sensitivity to ethylene and thereby slowing down wilting and subsequent plant death. The most widely used of these chemicals, STS, is a polluting metal salt and is both toxic and a skin irritant.

The enzyme 1-aminocyclopropane-1-carboxyllic acid (ACC) synthase, normally found in carnations, is responsible for the conversion of s-adenosylmethionine to ACC, which is the immediate precursor of ethylene. The transgenic carnation line 66 was developed using recombinant DNA techniques to display suppressed ACC synthase activity, and thus reduced ethylene synthesis and therefore longer vase life, by inserting an additional truncated copy of the ACC synthase encoding gene. The presence of the truncated ACC synthase gene suppresses the normal expression of the native ACC synthase gene, and while not completely understood, the mechanism of “downregulation” is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated ACC synthase gene.

Carnation line 66 was field tested in the United States, United Kingdom, the Netherlands, and Australia. Results demonstrated that genetically modified carnations had a vase life in water of 22 days, without requiring chemical treatment with STS or AOA. In the same study, non-genetically modified carnations only had a vase life in water of 10 days, and required treatment with STS or AOA to guarantee a vase life in water of at least 8 days.

The biology of carnation is such that there are no reasonable means for the genetically modified plants to escape from cultivation and become established as populations in the wild, or for gene dispersal from the genetically modified carnation to occur. The commercial standard carnation varieties are generally male sterile and rarely produce anthers; and if they do, little pollen is produced and this can only be transferred by insects. In commercial carnation production, outcrossing is unlikely as flowers are cut before opening. Should flowers open, only certain insects are easily able to access nectaries in flowers and there are very few opportunities for this to occur during transit and sale. Furthermore, carnations plants require 6 weeks for seed development. A genetically modified cut carnation flower lasts only 3-4 weeks, which is not enough time for seed set.

Many Dianthus species occur as common wildflowers in Canada and the United States. There has never been any evidence of hybridization between carnation and these species, nor after decades of cultivation have carnations been found in the wild. Carnation has no weedy characteristics and is not closely related to known weeds. The risk of transferring genetic traits from transgenic carnation line 66 to species in unmanaged environments was insignificant.

Links to Further Information Expand

Australian Genetic Manipulation Advisory Committee (GMAC)

This record was last modified on Wednesday, February 17, 2016