Transgenic Plants for Floriculture, Production of Transgenic Ornamental Plants, Transformation Procedures, Daffodils

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Home >> Plant Biotechnology and Genomics >> Genetically Modified-GM Crops and Floricultural Plants >> Transgenic Plants for Floriculture

	Transgenic Plants for Floriculture During 1990s, the interest in the production of transgenic ornamental plants also gained momentum. While in 1990, transformation procedure was available for only one ornamental i.e. Petunia, in 1995-2000, transformation procedures became available for many ornamentals including some monocots. These cut-flower species include rose, carnation, tulip, chrysanthemum, gerbera, daffodils, gypsophilla, lily, iris, etc. In several of these cut t1owers, recent work led to successful production of transgenics with novel aesthetic properties including novel colours, fragrance, plant and t1ower architecture, longer life, etc. Some of these traits having a commercial demand have been the target for genetic engineering and will be briet1y discussed.
Plant size The ratio of concentrations of cytokinin and auxin can be altered in transgenic plants through expression of oncogenes derived from Ti/Ri plasmids. Following are some examples: (i) Constitutive expression of rolc gene encoding cytokinin-β-glucosidase from Ri Plasmid leads to release of active cytokinins giving desired dwarf and bushy phenotype (e.g. potato becoming an ornamental). (ii) GA concentration can be altered, so that reduced GA can give dwarf plants and increased GA can give tall plants; two genes (gal, anl) involved in GA biosynthesis can be used to alter the levels of GA; overexpression of phytoene synthase gene also leads to reduced GA level and dwarfism.
Flower colour The first application of genetic engineering to modify flower colour led to the production of an orange pelargonidin-producing Petunia variety, which produced flowers pale brick colour. This was achieved by the expression to the dihydroflavonal-4 reductase gene (dfr) from maize in a petunia line. The variety was unstable due to transgene silencing and was therefore not viable in commercial market. Subsequently several transgenic plants with dfr gene were used for breeding with elite material to produce a commercially viable brown orange petunia variety in the Netherlands.
Production of blue flower in rose, tulip or carnation has also been an excitement among biotechnologists and floriculturists. It is complicated, because it needs following three factors: (i) synthesis of 3', 5' hydroxylated anthocyanins (delphinidins); (ii) presence of t1avonal co-pigments and (iii) relatively high vacuolar pH. Delphinidins are not available in roses, but two genes responsible for blue colour that have been isolated from petunias include the following: (i) gene for enzyme flavonoid-3'-5' hydroxylase (for synthesis of delphinidins) and (ii) gene for t1avonal synthase (for synthesis of t1avonals).
	The genes that control vacuolar pH were difficult to clone but some progress has been made. From six genes (pH l-pH6), pH6 had been cloned, and pH3 and pH4 were being cloned in 1995. Three other genes involved in regulation of anthocyanin biosynthetic pathway i.e. an1, an2 and an11 also cause alterations in intracellular pH and can be isolated by differential screening of cDNA library. Chalcone synthase (Chs) is another gene which has been used for production of pink, white and variegated flowers (sense and antisense genes were used) in -petunias, chrysanthemum, gerbera and roses. Transcriptional activators of anthocyanin biosynthetic pathway, namely R and CI have also been used to alter the intensity of flower colour. Mutations in regulatory sequence also gave novel pigmentation patterns in ornamentals like snapdragon. The gene Chs has also been used to produce white moneymaker chrysanthemum.

Architecture of flower and inflorescence

The identity of floral organs can be altered by using homeotic genes involved in determining the identity of floral whorls and the number of organs in each whorl. Mutants in Petunia and Arabidopsis have been isolated, which have altered number of floral organs. These can be used to change the architecture of the flower.

The inflorescence in ornamentals may have determinate (terminal flowers) or indeterminate growth (indefinite number of flowers). A single gene is sufficient to convert the inflorescence from indeterminate to determinate type or vice versa. Several of these genes have already been cloned.

Flowers with longer life

The vase life of flowers can be altered by manipulating the biosynthesis of ethylene. The enzymes ACC synthase and ACC oxidase are encoded by genes acs and aco respectively and both have been cloned from many species including carnation. Transgenic carnation having antisense aco gene or sense acs gene have been produced and exhibited longer vase-life (delay in petal senescence). They have already been approved for commercial release.

Other strategies for longer vase-life of flower including the following (i) overexpression of a gene for ACC deaminase, that metabolises ACC before it is converted to ethylene; (ii) overexpression of the gene for SAM hydrolase (isolated from T3 phage); (iii) expression of a gene for isopentenyl transferase (ipt) giving increased level of cytokinin; (iv) isolation and use of genes involved in ethylene signal transduction pathway.

Flower fragrance

Monoterpens are an important class of compounds that are involved in fragrance and are commercially valuable as essential oils for perfumes. These are derived from geranyl pyrophosphate by various monoterpene synthases, and a gene for one of them (S-linalool synthase) was cloned during early 1990s. Two other genes modifying monoterpenes were also cloned. These genes will be used in genetic engineering to modify floral fragrance.

Biosynthesis of ethylene and its Manipulation for Longer Vase Life

Biosynthesis of Ethylene and its Manipulation for Longer Vase Life

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