Generation of Yellow Flowers of the Japanese Morning Glory by Engineering Its Flavonoid Biosynthetic Pathway toward Aurones

Abstract

Wild-type plants of the Japanese morning glory (Ipomoea nil) produce blue flowers that accumulate anthocyanin pigments, whereas its mutant cultivars show wide range flower color such as red, magenta and white. However, I. nil lacks yellow color varieties even though yellow flowers were curiously described in words and woodblocks printed in the 19th century. Such yellow flowers have been regarded as ‘phantom morning glories’, and their production has not been achieved despite efforts by breeders of I. nil. The chalcone isomerase (CHI) mutants (including line 54Y) bloom very pale yellow or cream-colored flowers conferred by the accumulation of 2′, 4′, 6′, 4-tetrahydoroxychalcone (THC) 2′-O-glucoside. To produce yellow phantom morning glories, we introduced two snapdragon (Antirrhinum majus) genes to the 54Y line by encoding aureusidin synthase (AmAS1) and chalcone 4′-O-glucosyltransferase (Am4′CGT), which are necessary for the accumulation of aureusidin 6-O-glucoside and yellow coloration in A. majus. The transgenic plants expressing both genes exhibit yellow flowers, a character sought for many years. The flower petals of the transgenic plants contained aureusidin 6-O-glucoside, as well as a reduced amount of THC 2′-O-glucoside. In addition, we identified a novel aurone compound, aureusidin 6-O-(6″-O-malonyl)-glucoside, in the yellow petals. A combination of the coexpression of AmAS1 and Am4′CGT and suppression of CHI is an effective strategy for generating yellow varieties in horticultural plants.

Contribution of phenylpropanoid metabolism to plant development and plant–environment interactions

“…Genetically engineered plants with altered lignin composition and content are being applied in the pulp and paper industry to improve pulp yields and decrease energy consumption and environmental pollution, and in forage grasses to improve digestibility (Chabannes et al, 2001; Chanoca et al, 2019; Halpin, 2019). In addition, MFR through manipulation of flavonoid structural genes gives rise to flowers with novel colors in horticultural plants (Hoshino et al, 2019). With the rapid advancement of metabolic engineering and precise genome editing, the genetic control of metabolic flux of phenylpropanoid metabolism using a molecular design strategy is a promising approach to breeding high‐yield, stress‐resistant, and high‐nutritional content crops.…”

Chemical Constituents and Molecular Mechanism of the Yellow Phenotype of Yellow Mushroom (Floccularia luteovirens)

“…As it is a food with high nutritional value, research on yellow mushroom is imminent, but the molecular mechanisms of the yellow phenotype are still unclear. So far, a number of studies have reported that carotenoids, flavonoids, and other compounds contribute to the yellow flower color or fruit color of angiosperms, but few studies focus on fungi [ 11 , 12 ]. In the absence of chloroplasts, the yellow phenotype of yellow mushroom may be quite different [ 13 , 14 ].…”

The Flavonoid Biosynthesis Network in Plants

“…AS, a homolog of plant polyphenol oxidase (PPO), catalyzes the 4-monohydroxylation or 3,4-dihydroxylation of ring B to produce aurone, followed by oxidative cyclization by oxygenation [ 49 ]. Both in Ipomoea nil [ 50 ] and Torenia [ 45 ], the co-overexpression of the AmCH4′GT and AmAS1 genes leads to the accumulation of aurone 6- O -glucoside. Furthermore, various classical substitution patterns, such as hydroxylation, methoxylation, and glycosylation, lead to the formation of a series of aurone compounds, with over 100 structures having been reported to date [ 48 ].…”