Recent advances in flower color variation and patterning of Japanese morning glory and petunia

Abstract

The Japanese morning glory (Ipomoea nil) and petunia (Petunia hybrida), locally called “Asagao” and “Tsukubane-asagao”, respectively, are popular garden plants. They have been utilized as model plants for studying the genetic basis of floricultural traits, especially anthocyanin pigmentation in flower petals. In their long history of genetic studies, many mutations affecting flower pigmentation have been characterized, and both structural and regulatory genes for the anthocyanin biosynthesis pathway have been identified. In this review, we will summarize recent advances in the understanding of flower pigmentation in the two species with respect to flower hue and color patterning. Regarding flower hue, we will describe a novel enhancer of flavonoid production that controls the intensity of flower pigmentation, new aspects related to a flavonoid glucosyltransferase that has been known for a long time, and the regulatory mechanisms of vacuolar pH being a key determinant of red and blue coloration. On color patterning, we describe particular flower patterns regulated by epigenetic and RNA-silencing mechanisms. As high-quality whole genome sequences of the Japanese morning glory and petunia wild parents (P. axillaris and P. inflata, respectively) were published in 2016, further study on flower pigmentation will be accelerated.

CmMYB#7, an R3 MYB transcription factor, acts as a negative regulator of anthocyanin biosynthesis in chrysanthemum

“…Flower color variations often occur spontaneously in ornamental plants and produce various color hues and pigmentation patterning (venation, stripes, spots, and blotches) (Shang et al , 2011; Morita and Hoshino, 2018). Such floral color alterations are associated mainly with expression changes in pigment-related genes.…”

Ectopic Expression of PAP1 Leads to Anthocyanin Accumulation and Novel Floral Color in Genetically Engineered Goldenrod (Solidago canadensis L.)

“…Alternatively, post-transcriptional gene silencing may be responsible for the color patterning, as found for petunia cvs. Night Sky, Picotee and Star, where small interfering RNA accumulates in the white sections and spatially represses the biosynthetic enzyme chalcone synthase, resulting in a bicolored phenotype (Koseki et al, 2005; Saito et al, 2006; Morita and Hoshino, 2018). Future genomic/transcriptomic studies integrated with analyses of metabolic shunts in transgenic tissues should provide new insights into the machinery regulating phenylpropanoid biosynthesis in Solidago .…”

A P3A-Type ATPase and an R2R3-MYB Transcription Factor Are Involved in Vacuolar Acidification and Flower Coloration in Soybean

“…The early steps in the anthocyanin biosynthesis pathway are catalyzed by chalcone synthase, chalcone isomerase, and flavanone 3-hydroxylase, whereas the later steps are mediated by dihydroflavonol-4-reductase, anthocyanin synthase, and flavonoid 3-O-glucosyltransferase (3GT) (Morita and Hoshino, 2018). Anthocyanidin 3-glucosides are the first stable anthocyanins synthesized by 3GT-catalyzed glycosylation at the third carbon position of anthocyanidin aglycones (Morita and Hoshino, 2018).…”

“…The early steps in the anthocyanin biosynthesis pathway are catalyzed by chalcone synthase, chalcone isomerase, and flavanone 3-hydroxylase, whereas the later steps are mediated by dihydroflavonol-4-reductase, anthocyanin synthase, and flavonoid 3-O-glucosyltransferase (3GT) (Morita and Hoshino, 2018). Anthocyanidin 3-glucosides are the first stable anthocyanins synthesized by 3GT-catalyzed glycosylation at the third carbon position of anthocyanidin aglycones (Morita and Hoshino, 2018). In most higher plants, the anthocyanin biosynthesis pathway is reportedly regulated by a MBW complex comprising transcription factors that contain MYB, basichelix-loop-helix (bHLH), and WD-repeat (WD40) domains (Hartmann et al, 2005;Lepiniec et al, 2006;Quattrocchio et al, 2006a;Solfanelli et al, 2006;Gonzalez et al, 2008;Albert et al, 2014).…”