The Balance of Expression of Dihydroflavonol 4-reductase and Flavonol Synthase Regulates Flavonoid Biosynthesis and Red Foliage Coloration in Crabapples

Abstract

Red leaf color is an attractive trait of Malus families, including crabapple (Malus spp.); however, little is known about the molecular mechanisms that regulate the coloration. Dihydroflavonols are intermediates in the production of both colored anthocyanins and colorless flavonols, and this current study focused on the gene expression balance involved in the relative accumulation of these compounds in crabapple leaves. Levels of anthocyanins and the transcript abundances of the anthocyanin biosynthetic gene, dihydroflavonol 4-reductase (McDFR) and the flavonol biosynthetic gene, flavonol synthase (McFLS), were assessed during the leaf development in two crabapple cultivars, ‘Royalty’ and ‘Flame’. The concentrations of anthocyanins and flavonols correlated with leaf color and we propose that the expression of McDFR and McFLS influences their accumulation. Further studies showed that overexpression of McDFR, or silencing of McFLS, increased anthocyanin production, resulting in red-leaf and red fruit peel phenotypes. Conversely, elevated flavonol production and green phenotypes in crabapple leaves and apple peel were observed when McFLS was overexpressed or McDFR was silenced. These results suggest that the relative activities of McDFR and McFLS are important determinants of the red color of crabapple leaves, via the regulation of the metabolic fate of substrates that these enzymes have in common.

McMYB12 Transcription Factors Co-regulate Proanthocyanidin and Anthocyanin Biosynthesis in Malus Crabapple

“…We previously reported that the anthocyanin concentration in ever-red leaves, was significantly higher than that in ever-green leaves17, and that a competitive relationship between anthocyanin and flavonol is important for leaf coloration46. We characterized PAs accumulation patterns during five leaf developmental stages (1–5) of the ever-red leaf cultivar ‘Royalty’ and the ever-green leaf cultivar ‘Flame’, using high pressure liquid chromatography (HPLC) (Fig.…”

“…In addition, up-regulation in the expression of the PAs regulator McMYB12b significantly enhanced the accumulation of PAs, and inhibited the biosynthesis of anthocyanins (Figs 6A and 8). We deduced from these data that there is a metabolic balance between flavonol and anthocyanin biosynthesis46, and that the anthocyanin and PAs biosynthetic pathways have a competitive relationship in crabapple leaves. The massive expression of McCHS , an upstream enzyme in flavonoids biosynthesis, may promote the accumulation of anthocyanins in McMYB12a -overexpression lines.…”

“…The infiltration protocol and culture methods for apple fruits were adapted as previously described46.…”

Identification of Genes Involved in Flavonoid Biosynthesis in Sophora japonica Through Transcriptome Sequencing

“…Upon silencing of Nt FLS in tobacco by RNAi, the content of flavonol in transgenic plants decreased by 25 – 93%, while the contents of catechins, epicatechin and epigallocatechin increased . Overexpression of McFLS in Malus crabapple using transient expression systems revealed significant increase in flavonol content at the injection site and significant decrease in anthocyanin content . Thus, there was competitive relationship between production of flavonols and anthocyanins.…”

An optimized TRV-based virus-induced gene silencing protocol for Malus crabapple

“…Stem tips were used as explants and the explants of the two cultivars were harvested from 1 year-old branches before spring bud germination. Stem tip sections were rinsed with water for 2 h and disinfected with 0.15 % HgCl 2 for 8 min 2.0-3.0 mm long stem tips were cultured on Murashige and Skoog (MS) medium supplemented with 0.1 mg/L 6-BA and 2.0 mg/L 2, 4-D at 23°C for a 16 h light (200 lmol s -1 m -2 )/8 h dark period for 60 days, prior to Plant Cell Tiss Organ Cult VIGS infiltration (Tian et al 2015a). After infiltration, all crabapple tissue culture plantlets were rinsed with distilled water and cultured in MS medium supplemented with 50 mg/L kanamycin and 100 mg/L sodium cefotaxime.…”