By Naonobu Noda and Yoshikazu Tanaka
Chrysanthemums (Chrysanthemum morifolium) are the second best-selling flowers after roses in the world. In Japan, they are by far the most popular and the 16 petal chrysanthemum with sixteen tips represents the Imperial Crest. Cultivated chrysanthemums have been generated by hybridization breeding of many wild species for hundreds or possibly thousands of years. Their flowers are pink, red, magenta, yellow, or white, but never violet-blue because chrysanthemums lack the key gene (the so-called blue gene, flavonoid 3′,5′-hydroxylase (F3′5′H) gene) to synthesize the delphinidin-based pigments which most violet-blue flowers accumulate.
Bluish-colored cultivars are not available in major cut flowers such as rose, carnation, chrysanthemum, lily, and gerbera due to the deficiency of F3′5′H gene. Genetic engineering techniques have enabled expression of the F3′5′H gene in rose (Rosa hybrida) and carnation (Dianthus caryophyllus) leading to novel varieties with violet-blue hued flowers accumulating delphinidin-based anthocyanins. The color-modified carnations are sold in USA, EU, Japan, and other countries; the rose is sold only in Japan. Until now comparable genetically modified chrysanthemum varieties had not been developed due to recalcitrant and unpredictable expression of introduced genes; the chrysanthemum tends to shut them off by as yet unknown mechanisms.
For the first time, research teams at Florigene, Suntory, and at NARO Institute of Floricultural Science (NIFS) developed distinct genetic engineering approaches to create the long-desired violet-blue chrysanthemums, the results of which were recently reported in two papers published in the international journal Plant and Cell Physiology.
After incalculable trial and error experiments over the past 15 years, two tactics have now been found to be effective for creation of stable color modified chrysanthemum varieties. The NIFS and Suntory team of Naonobu Noda et al. optimized F3′5′H transgene expression in decorative-type chrysanthemums. They found that the use of a petal-specific promoter (the DNA sequence which lets genes work) from chrysanthemum flavanone 3-hydroxylase gene driving a canterbury bells (Campanula medium) F3′5′H gene is most suitable for production of delphinidin-base anthocyanin in the petals of chrysanthemum. The content of delphinidin in the petals of the transgenic chrysanthemum ranged as high as 95% of total anthocyanin and substitution of anthocyanin chromophore from cyanidin to delphinidin dramatically changed chrysanthemum ray floret color from magenta/pink to purple/violet.
In a second approach, described by Filippa Brugliera et al., the team of Florigene and Suntory found that expression of a pansy F3′5′H gene under the control of a chalcone synthase promoter from rose resulted in the effective diversion of the anthocyanin pathway to delphinidin, producing transgenic daisy-type chrysanthemums. The resultant flower color was bluish with 40% of total anthocyanidins based on delphinidin. Even higher levels of delphinidin (up to 80%) were achieved by down- regulation of the pathway leading to cyanidin-based pigments.
In both studies, delphinidin accumulation led to changes to bluish flower color hues unable to be obtained by conventional chrysanthemum breeding. The new flower color seems to be stable (and consistently beautiful!) in glasshouse trials. Since they are genetically modified plants, government permissions are necessary to release them to the environment for commercialization. This may present a significant challenge, as absolute sterility may be required in some countries to prevent out crossing to wild species.
Nevertheless, these findings have opened the door to more colorful chrysanthemums at the florist. Both teams continue their research: to obtain flowers with a sky blue color and varieties with sterility.
Naonobu Noda is a senior researcher at NARO Institute of Floricultural Science (NIFS), Japan. In 1995, he graduated from the Faculty of Agriculture, Tokyo University of Agriculture and in 2000 he obtained his Ph.D. in Agriculture at Kagoshima University. After moving to Aomori Green BioCenter, Aomori Prefectural Agriculture and Forestry Research Center (from 2000-2007), he joined NIFS where his research focuses on the development of blue-colored chrysanthemums. He is co-author of the paper ‘Genetic Engineering of Novel Bluer-Colored Chrysanthemums Produced by Accumulation of Delphinidin-Based Anthocyanins’, which appears in Plant Cell Physiol (2013) 54 (10): 1684-1695 (doi: 10.1093/pcp/pct111).
Yoshikazu Tanaka is general manager at the Research Institute of Suntory Global Innovation Center Ltd. After gaining a master’s degree from Osaka University, he joined Suntory Ltd. and obtained a doctoral degree at Osaka University. Since 1990, he has been working on genetic engineering of flower color modification and has successfully generated and commercialized novel blue/violet hued transgenic carnations and roses, also published in Plant & Cell Physiology (Plant Cell Physiol (1998) 39 (11): 1119-1126 and Plant Cell Physiol (2007) 48 (11): 1589-1600; doi:10.1093/pcp/pcm131, respectively). His latest work on the generation of violet/blue Chrysanthemums is reported in Plant Cell Physiol (2013) 54 (10): 1684-1695 (doi: 10.1093/pcp/pct111) and in Plant Cell Physiol (2013) 54 (10): 1696-1710 (doi: 10.1093/pcp/pct110).
Plant & Cell Physiology (PCP) is an international journal publishing high quality original research articles on broad aspects of biology, physiology, biochemistry, biophysics, chemistry, molecular genetics, epigenetics, and biotechnology of plants and interacting microorganisms.
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Image credits: All images courtesy of the scientists via Plant & Cell Physiology. Do not reproduce without prior written permission.