Spontaneous mutations of the UDP-glucose:flavonoid 3-O-glucosyltransferase gene confers pale- and dull-colored flowers in the Japanese and common morning glories
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UDP-glucose:flavonoid 3- O -glucosyltransferase is essential for maintaining proper production quantity, acylation, and glucosylation of anthocyanin, and defects cause pale and dull flower pigmentation in morning glories.
The Japanese (Ipomoea nil) and the common (I. purpurea) morning glory display bright blue and dark purple flowers, respectively. These flowers contain acylated and glucosylated anthocyanin pigments, and a number of flower color mutants have been isolated in I. nil. Of these, the duskish mutants of I. nil produce pale- and dull-colored flowers. We found that the Duskish gene encodes UDP-glucose:flavonoid 3-O-glucosyltransferase (3GT). The duskish-1 mutation is a frameshift mutation caused by a 4-bp insertion, and duskish-2 is an insertion of a DNA transposon, Tpn10, at 1.3 kb upstream of the 3GT start codon. In the duskish-2 mutant, excision of Tpn10 is responsible for restoration of the expression of the 3GT gene. The recombinant 3GT protein displays expected 3GT enzymatic activities to catalyze 3-O-glucosylation of anthocyanidins in vitro. Anthocyanin analysis of a duskish-2 mutant and its germinal revertant showing pale and normal pigmented flowers, respectively, revealed that the mutation caused around 80 % reduction of anthocyanin accumulation. We further characterized two I. purpurea mutants showing pale brownish-red flowers, and found that they carry the same frameshift mutation in the 3GT gene. Most of the flower anthocyanins in the mutants were previously found to be anthocyanidin 3-O-glucosides lacking several caffeic acid and glucose moieties that are attached to the anthocyanins in the wild-type plants. These results indicated that 3GT is essential not only for production, but also for proper acylation and glucosylation, of anthocyanin in the morning glories.
KeywordsAnthocyanin Flavonoid Flower pigmentation Ipomoea
Quantitative reverse transcription-PCR
We thank Dr. Norio Saito for his participation in valuable discussions, Miwako Matsumoto, Chisato Matsuda, Ryoko Nakamura, Tomoyo Takeuchi, and Kazuyo Ito for their technical assistance, and the NIBB Model Plant Research Facility and the NIBB Functional Genomics Facility for the technical support. We also thank the National Bioresource Project Morning Glory and Dr. Eiji Nitasaka for Ipomoea seeds. This work was supported by grants, Grant-in-Aid for Scientific Research (No. 17207002 to S. I. and No. 18770041 to A. H.) from the Ministry of Education, Culture, Sports, Science and Technology.
Conflict of interest
The authors declare that they have no conflict of interest.
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