Role of Biotechnological Interventions in Improving the Traits of Flowering Ornamentals

Received 31 Mar, 2023

Accepted 27 Aug, 2023

Published 30 Sep, 2023

Improving the floricultural traits in ornamentals is of great value in floriculture and landscaping. Conventional methods have been and are being still used for improving the floricultural traits like vase life or floral longevity, ethylene sensitivity and visible floral morphological features, etc. in ornamentals by postharvest application of ethylene antagonists, plant growth regulators, sugar sources, protein synthesis inhibitors and antimicrobial compounds, etc. However, biotechnology offers a promising approach to improving the desirable attributes in flowering ornamentals like flower color, fragrance, longevity, ethylene insensitivity, disease resistance, etc. In the present review, the biotechnological interventions in enhancing the flower fragrance, flower color and flower longevity/vase life have been discussed and a number of suitable examples related to the improvement of these traits in various ornamentals have been provided. The mini-review intends to present a comprehensive update of the available literature regarding the improvement of these traits in flowering ornamentals involving the non-conventional biotechnological approach.

INTRODUCTION

Floriculture or flower farming, one of the important horticultural disciplines, primarily focuses on various parameters related to ornamentals that include their propagation, cultivation, harvesting, as well as postharvest processing. Efforts have been made and are being made to improve the floral attributes so as to make them more market-oriented. The research leading to the improvement in the attributes of these ornamentals is being conducted at different levels-preharvest level, harvest and postharvest level. The preharvest level research parameters include the quality of the plant material (seed, bulb, rhizome, etc.), appropriate growing conditions (soil requirements, fertilizer application, water requirements, light conditions and temperature etc.) and protection from diseases and pests. Appropriate time of harvest, the right method and the right stage of harvest are the primary factors influencing the harvest stage. The postharvest level factors that influence the attributes of ornamentals include proper transportation and storage, use of chemical preservatives and growth regulators as pulse or spray treatments, maintenance of sugar supply, use of antimicrobial agents in vase solutions, use of ethylene antagonists and optimum ranges of temperature and relative humidity, etc. A number of floral attributes like size, longevity and quality have been improved to a great extent by research at pre-harvest as well as postharvest level. Moreover, the intervention of biotechnology or genetic engineering has offered a promising approach for developing new ornamentals with improved floral attributes as well as producing ornamentals with novel traits. Altered flower colour, enhanced fragrance, disease resistance, ethylene in-sensitivity (in ethylene-sensitive flowers) and early blooming are some of the important attributes that have been targeted using biotechnological interventions^1-4. The present review intends to provide comprehensive information about the role of biotechnology in improving and modifying the attributes of ornamentals with the purpose to enhance their commercial value.

Flower fragrance: The flower fragrance has been attributed to the biosynthesis of many volatile compounds like terpenoids, benzenoids, phenylpropanoid and other Sulphur or Nitrogen-containing compounds⁵. Floral fragrance or scent production in ornamentals offers many advantages like a signal for pollinators, attraction for predators of herbivores and repulsion of herbivores, etc^5-7. A number of ornamentals have been genetically modified to enhance scent production. Some of the notable examples were listed in Table 1.

From Table 1, it is clear that scent production has been enhanced in the ornamentals by using two approaches i.e. either by inducing the production of volatile compounds like Benzyl acetate and S-linalool or by regulating the expression of the F3'H gene (downregulation in Carnation) or PAP1 gene (Overexpression in Rose). Here, it deserves mention that the AtPAP1 gene is responsible for flower color modification as well as for enhancing the fragrance.

Flower color: Another important attribute of ornamentals is the floral display in the form of various colors which has been attributed to the occurrence of different plant pigments in the floral organs. These pigments include anthocyanins, chlorophylls, carotenoids, betalains, etc. These pigments are known to play important roles like attraction to pollinators, light capturing for photosynthesis and protection from UV radiation besides determining the ornamental value of the plants¹². Many ornamentals have been genetically engineered to produce flowers with novel colors or enhanced colors. Some of the notable examples were listed in Table 2.

A number of flowers with novel or enhanced flower colors have been obtained using the biotechnological approach (Table 2) wherein the genes like DFR gene, F3’H genes, F3’5’H genes and PAP1 gene have been introduced to host ornamentals and made to express and produce the novel phenotype. Moreover, the silencing or down regulation of genes like the CHS gene (Chalcone synthase), ANS gene, F3’5’H genes and the overexpression of the PAP1 gene and CrtW gene have been found to enhance or modify the flower color in many ornamentals.

Vase life/shelf life: Another important parameter that determines the postharvest quality of ornamentals is their vase life or shelf life. Flower longevity or vase life determines how long a flower or a spike or scape remains in fresh condition after being detached from the mother plant, particularly in the case of cut flowers. A number of preharvest and postharvest treatments are known to enhance the vase life or shelf life of ornaments by conventional use of Plant Growth Regulators (PGRs) and vase solutions containing sugars, sugar alcohols, biocides, ethylene antagonists and other chemicals^33,34. However, genetic engineering has also been employed to produce ornamentals with enhanced shelf life/vase life. Some of the notable examples were listed in Table 3.

Table 1:

Genetic modification in ornamentals for flower fragrance

Plant	Gene	Source	References
Carnation and lisianthus	LIS gene that codes S-linalool synthase	Clarkia breweri	Zaccai et al.8
Carnation	Downregulation of the F3H gene	Carnation	Zuker et al.9
Lisianthus	Benzyl alcohol acetyl transferase (BEAT) for the production of benzyl acetate	Clarkia breweri	Aranovich et al.10
Rosa hybrida	Overexpression of the AtPAP1 gene	Arabidopsis thaliana	Zvi et al.11

Table 2:

Genetic modification in ornamentals for flower color

Plant	Gene	Source	Altered flower color	Reference number
Petunia (deficient in	DFR gene	Maize	Orange	Meyer et al.13 and Meyer et al.14
F3’5’H and F3’H)				Forkmann et al.15
Chrysanthemum	Expressing sense or	-	White or light pink	Courtney-Gutterson et al.16
(Pink)	antisense copies of the Chs gene encoding chalcone synthase
Carnation (White)	F3'5'H and DFR gene	Petunia	Blue (FLORIGEN) E®Moondust™)	Lou et al.17
Carnation (white)	F3'5'H and DFR gene	Viola and Petunia,	Dark violet	Mol et al.18
		respectively	FLORIGENE®
			Moonshadow™
Arabidopsis and	Overexpression of	Arabidopsis AtMYB75,	Flowers with enhanced	Borevitz et al.19
Tobacco	PAP1	(PAP1 transcription factor)	pigmentation
Carnation	Antisense gene construct for F3'H gene	Carnation	White	Zuker et al.9
Petunia	Down regulation of F3'H gene (petunia) and over expression of rose DFR gene	Rosa	Red	Tsuda et al.20
Rose	F3'5'H gene	Viola	Blue rose	Katsumoto et al.21
Torenia	Anthocyanin biosynthesis genes (by employing RNAi)	Torenia	White	Nakamura et al.22
Torenia (Blue)	Down regulation of F3'5'H and F3'H genes and over expression of Pelargonium DFR gene	Pelargonium	Pink	Nakatsuka et al.23
Tobacco	Down regulation of	Gerbera	Red	Nakatsuka et al.23
	F3'H gene and flavonol synthase gene and overexpression of gerbera DFR gene
Lotus japonica	Overexpression	Lotus japonica	Deep yellow to	Suzuki et al.24
	of CrtW gene		orange
Gentiana	Suppression of the	Gentiana	Magenta	Nakatsuka et al.25
	F3'5'H gene
Gentian	Silencing of CHS	Gentian	White and pale blue,	Nakatsuka et al.25 and
	and ANS genes		respectively	Yoshida et al.26
Gentian	Downregulating the F3’5’H gene and the 5,3’-AT gene (encoding anthocyanin)	Gentian	Pink	Nakatsuka et al.25
Chrysanthemum	Expressing F3’5’H gene under rose CHS promoter	-	Blue	Nakatsuka et al.27
Chrysanthemum	Suppression of CmCCD4a	Chrysanthemum	Yellow	Ohmiya et al.28 and
	(Carotenoid cleavage dioxygenase) gene		(Yellow Jimba)	Ohmiya et al.29
Lilium	PhF3'5'H gene	Phalaenopsis	Purple	Azadi et al.30
Cyclamen persicum	Suppression of the	Cyclamen	Red/Pink	Boase et al.31
(Purple)	F3'5'H gene
Chrysanthemum	Suppression of	Chrysanthemum	Bright red	He et al.32
	CmF3’H gene

Table 3:

Genetic modification in ornamentals for enhanced vase life

Plant	Gene	Source	References
Carnation	Silencing the ACO gene	-	Savin et al.35
Carnation	etr1-1 gene	Arabidopsis	Bovy et al.36
Petunia	Transformation of etr1-1 gene	Arabidopsis	Gubrium et al.37
Chrysanthemum			Ma et al.38
Carnation	ACO gene and ACS gene	Carnation and apple	Inokuma et al.39
Oncidium	Mutating ethylene receptor gene	-	Raffeiner et al.40
Odontoglossum	Mutating ethylene receptor gene	-	Raffeiner et al.40

Another feature added to the cap of ornamental biotechnology is the development of fluorescent flowers in Torenia by using a yellowish-green fluorescent gene-CpYGFP from the marine plankton Chiridius poppei⁴¹. These fluorescent ornamentals serve the dual purpose-one being the enhancement of the ornamental value of the plant and the other being used for the analysis of fluorescent transgenic plants spatiotemporally in a non-destructive manner.

CONCLUSION

In conclusion, biotechnology involving the genetic engineering approach has not only provided a significant contribution to modifying or improving the existing traits of flowering ornamentals but has led to the production of ornamentals with novel traits. These modifications in ornamentals have been proven to be a successful venture from scientific as well as commercial points of view. As far as the future perspective of ornamental horticulture is concerned, biotechnology has an important role to play which involves the extension of the existing biotechnological strategies/approaches to other related ornamentals and to promote research in more areas related to flowering ornamentals.

SIGNIFICANCE STATEMENT

Biotechnology offers a promising approach to improve the traits of the ornamentals when compared to traditional methods of ornamental plant improvement. Using the biotechnological approach, many milestones have been achieved while dealing with ornamentals like enhancement of vase life or flower longevity, enhancing the floral fragrance/scent, modifying the flower color or producing flowers with novel colors and reducing sensitivity to ethylene, etc. The purpose of the mini-review was to present an update on the improvement of some selected traits in flowering ornamentals using the biotechnological approach. Many examples of genetic modifications in ornamentals have been provided in the review so as to comprehend the importance of biotechnology in ornamental horticulture.

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