Anthocyanin and Flavonol Glycoside Metabolic Pathways Underpin Floral Color Mimicry and Contrast in a Sexually Deceptive Orchid

Abstract

Sexually deceptive plants secure pollination by luring specific male insects as pollinators using a combination of olfactory, visual, and morphological mimicry. Flower color is a key component to this attraction, but its chemical and genetic basis remains poorly understood. Chiloglottis trapeziformis is a sexually deceptive orchid which has predominantly dull green-red flowers except for the central black callus projecting from the labellum lamina. The callus mimics the female of the pollinator and the stark color contrast between the black callus and dull green or red lamina is thought to enhance the visibility of the mimic. The goal of this study was to investigate the chemical composition and genetic regulation of temporal and spatial color patterns leading to visual mimicry, by integrating targeted metabolite profiling and transcriptomic analysis. Even at the very young bud stage, high levels of anthocyanins were detected in the dark callus, with peak accumulation by the mature bud stage. In contrast, anthocyanin levels in the lamina peaked as the buds opened and became reddish-green. Coordinated upregulation of multiple genes, including dihydroflavonol reductase and leucoanthocyanidin dioxygenase, and the downregulation of flavonol synthase genes (FLS) in the callus at the very young bud stage underpins the initial high anthocyanin levels. Conversely, within the lamina, upregulated FLS genes promote flavonol glycoside over anthocyanin production, with the downstream upregulation of flavonoid O-methyltransferase genes further contributing to the accumulation of methylated flavonol glycosides, whose levels peaked in the mature bud stage. Finally, the peak anthocyanin content of the reddish-green lamina of the open flower is underpinned by small increases in gene expression levels and/or differential upregulation in the lamina in select anthocyanin genes while FLS patterns showed little change. Differential expression of candidate genes involved in specific transport, vacuolar acidification, and photosynthetic pathways may also assist in maintaining the distinct callus and contrasting lamina color from the earliest bud stage through to the mature flower. Our findings highlight that flower color in this sexually deceptive orchid is achieved by complex tissue-specific coordinated regulation of genes and biochemical pathways across multiple developmental stages.

Metabolic profile and transcriptome reveal the mystery of petal blotch formation in rose

“…No avone but only avonols were also detected in petals of Rhododendron, except for quercetin glycosides and kaempferol glycosides, gossypetin, myricetin, and azaleatin derivatives also existed [49]. The same phenomenon can also be seen in orchid, besides quercetin glycosides and kaempferol glycosides, isorhamnetin derivatives also existed [50]. In petals of other plants, avone and avonol usually coexist.…”

Conserved pigment pathways underpin the dark insectiform floral structures of sexually deceptive Chiloglottis (Orchidaceae)

“…Developmental stage and tissue-specific differential expression of genes encoding dihydroflavonol reductase, leucoanthocyanidin dioxygenase, flavonol synthase, and flavonoid O-methyltransferase that controls specific branch point into respective anthocyanin and flavonol glycoside biosynthesis (and their methylated derivatives) may also assist in maintaining the color from the earliest bud stage through to the mature flower. These findings highlight the multi-gene and regulatory complexity of the floral color adaptations involved in securing pollination by sexual deception ( Wong et al, 2022 ).…”

“…Our study builds on this large body of prior work, and in particular on recent work on the chemical composition and genetic regulation of the temporal and spatial color patterns underpinning the visual mimicry in Chiloglottis trapeziformis ( Wong et al, 2022 ). Targeted metabolite profiling in this species revealed that the localized distribution of abundant cyanidin-based anthocyanins and diverse flavonol glycoside co-pigments give the black callus structure its distinct dark color.…”

Integrated metabolic, transcriptomic and chromatin accessibility analyses provide novel insights into the competition for anthocyanins and flavonols biosynthesis during fruit ripening in red apple

“…Moreover, the numbers of increased DAMs belonging to phenolic acids, flavonoids, lipids, terpenoids, lignans and coumarins were much lower than the decreased ones in the comparison PS5_vs_PS1, but were much higher than the increased ones in the comparison PS9_vs_PS5, suggesting that the accumulations of these kinds of metabolites are associated with the red apple ripening process. Given that they share the same biosynthesis substrates, competition occurred between anthocyanins and flavonols biosynthesis pathways in many plants (Luo et al, 2016;Zhong et al, 2020;Wong et al, 2022). For example, a comparison of anthocyanins and flavonols contents in the petals of ten Rhododendron species revealed that species with low anthocyanin contents had high flavonols (Liu et al, 2016); in Malus, competition between anthocyanins and kaempferol glycosides was found to be related to pollen tube growth and seed set (Chen et al, 2021); in bilberry, procyanidins and quercetins were identified as the major flavonoids in the early fruit ripening stage, but anthocyanins accounted for the largest fraction in the later ripening stages (Jaakola et al, 2002).…”

“…By using the white-flowered, flavonol accumulating Mitchell line of petunia as material, Davies et al (2003) found that overexpression both of 35SCaMV-DFR sense and/or FLS antisense transgene led to the anthocyanins production and resulted in a pink-flowered phenotype. Constitutive overexpression of FLS genes from Rosa rugosa, Prunus persica, and Petunia hybrida in tobacco all resulted in white flowers, while the heterologous overexpression of DFR genes resulted in increased anthocyanins accumulations and redder flowers (Luo et al, 2016;Wong et al, 2022). Liu et al (2019b) reported that heterologous expression of the Muscari aucheri MaFLS gene in tobacco increased NtFLS expression, but inhibited the expression of tobacco anthocyanins biosynthesis genes, such as NtDFR, NtANS and NtAN2, and reduced the pigmentation of tobacco petals.…”