Figures (2)  Tables (3)

    • Figure 1.  General structure of (a) flavonol aglycones and (b) main glycosides.

    • Figure 2.  Representative flavonol biosynthetic pathways. The pathways utilize naringenin chalcone, produced from phenylalanine and malonyl-CoA, highlighted in grey. The metabolic pathway of 5,7-oxo flavonols is highlighted in yellow, and biosynthetic pathways for 5-deoxy flavonols are highlighted in green. CHR: chalcone reductase; CHI: chalcone isomerase; F3H: flavanone 3-hydroxylase; F3’H: flavonoid 3’-hydroxylase; F3’5’H: flavonoid 3’5’-hydroxylase; OMT: O-methyltransferases; FLS: flavonol synthase.

    • Aglycones56782’3’4’5’6’Reference
      KaempferolOHHOHHHHOHHH[16]
      QuercetinOHHOHHHOHOHHH[16]
      MyricetinOHHOHHHOHOHOHH[16]
      GalanginOHHOHHHHHHH[19,20]
      GossypetinOHHOHOHHOHOHHH[30]
      KaempferideOHHOHHHHOCH3HH[25]
      quercetagetinOHOHOHHHOHOHHH[31]
      LaricitrinOHHOHHHOCH3OHOHH[25]
      MorinOHHOHHOHHOHHH[17]
      IsorhamnetinOHHOHHHOCH3OHHH[16]
      NatsudaidainOCH3OCH3OCH3OCH3HHOCH3OCH3H[32]
      SyringetinOHHOHHHOCH3OHOCH3H[33]
      SexangularetinOHHOHOCH3HHOHHH[34]
      RhamnetinOHHOCH3HHOHOHHH[17]
      FisetinHHOHHHHOHOHH[17]

      Table 1.  Summary of flavonol aglycones identified in fruits.

    • Fruit speciesDivergent flavonolsReference
      Apple
      		Quercetin 3-O-rhamnoside; Quercetin 3-O-galactoside; Quercetin 3-O-arabinoside; Quercetin 3-O-glucoside; Quercetin 3-O-xyloside; Quercetin 3-O-robinobioside; Quercetin 3-O-rutinoside; Quercetin 3-O-neohesperidoside; Kaempferol 3-O-galactoside; Kaempferol 3-O-arabinoside; Isorhamnetin 3-O-galactoside; Isorhamnetin 3-O-glucoside; Rhamnetin 3-O-rutinoside[10,35]
      Pear
      		Quercetin 3-O-glucoside; Isorhamnetin 3-O-galactoside; Isorhamnetin 3-O-rutinoside; Isorhamnetin 3-O-malonylglucoside; Isorhamnetin hexoside; Isorhamnetin 3-O-malonylgalactoside; Isorhamnetin 3-O-glucoside; Isorhamnetin; Quercetin 3-O-galactoside; Quercetin 3-O-galactosyl-glucoside; Quercetin 3-O-rutinoside; Quercetin 3-O-arabinoside; Quercetin O-acetylhexoside; Quercetin 5-O-malonylhexosyl-hexoside; Quercetin 7-O-malonylhexosyl-hexoside; Quercetin 4’-O-glucoside; Kaempferol 3-O-galactoside; Kaempferol 3-O-rutinoside; Kaempferol 3-O-acetylglucoside; Kaempferol 3-O-rhamnoside; Rhamnetin hexoside;[21,36,37,38]
      Peach
      		Quercetin 3-O-glucoside; Isorhamnetin 3-O-rutinoside; Isorhamnetin 3-O-glucoside; Quercetin 3-O-rhamnoside; Quercetin 3-O-galactoside; Quercetin 3-O-rutinoside; Kaempferol 3-O-rutinoside; Kaempferol 3-O-glucoside[22,28]
      Loquat
      		Quercetin 3-O-glucoside; Quercetin 3-O-galactoside; Kaempferol 3-O-sophoroside; Quercetin 3-O-rhamnoside; Quercetin 3-O-rutinoside; Quercetin 3-O-neohesperidoside; Quercetin 3-O-sophoroside; Quercetin-3-O-galactosyl-glucoside; Quercetin 3-O-sambubioside; Kaempferol 3-O-neohesperidoside; Kaempferol 3-O-sambubioside; Kaempferol 3-O-rhamnoside; Kaempferol 3-O-glucoside; Kaempferol 3-O-rutinoside[39,40]
      Hawthorn
      		Quercetin 3-O-galactoside; Quercetin 3-O-glucoside; Quercetin 3-O-rutinoside;
      Kaempferol 3-O-glucoside; Kaempferol 3-O-neohesperidoside; Sexangularetin; Sexangularetin 3-O-neohesperidoside; Sexangularetin 3-O-glucoside      		[27,34]
      Grape
      		Quercetin 3-O-glucoside; Quercetin 3-O-glucuronide; Myricetin 3-O-glucoside; Quercetin 3-O-galactoside; Quercetin 3-O-rutinoside; Quercetin; Kaempferol 3-O-galactoside; Kaempferide coumaroylhexoside; Kaempferol 3-O-glucoside; Myricetin 3-O-glucuronide; Myricetin dihexoside; Myricetin glucoside-glucuronide; Isorhamnetin 3-O-glucoside; Isorhamnetin 3-O-glucoside; Isorhamnetin glucuronide; Isorhamnetin coumaroylglucoside; Isorhamnetin; Laricitrin 3-O-glucoside; Syringetin-dihexoside; Syringetin 3-O-glucoside; Syringetin 3-O-galactoside[18,23,41]
      Blueberry
      		Quercetin 3-O-galactoside; Quercetin 3-O-rhamnoside; Quercetin 3-O-rutinoside; Quercetin 3-O-glucoside; Quercetin 3-O-pentoside; Quercetin 3-O-glucoside acetate; Quercetin 3-O-arabinoside; Myricetin 3-O-galactoside; Myricetin 3-O-glucoside; Myricetin 3-O-pentoside; Myricetin 3-O-rhamnoside; Kaempferol 3-O-rutinoside; Kaempferol 3-O-glucoside; Laricitrin 3-O-galactoside; Laricitrin 3-O-glucoside; Laricitrin 3-O-rhamnoside; Laricitrin 3-O-pentoside; Isorhamnetin 3-O-galactoside; Isorhamnetin 3-O-rhamnoside; Isorhamnetin 3-O-glucoside; Syringetin 3-O-glucoside; Syringetin 3-O-rhamnoside; Syringetin 3-O-pentoside; Syringetin 3-O-galactoside[20,25,42]
      Bayberry
      		Myricetin 3-O-rhamnoside; Quercetin 3-O-galactoside; Quercetin 3-O-rhamnoside; Myricetin 3-O-glucoside; Myricetin deoxyhexoside-gallate; Quercetin 3-O-glucuronide; Quercetin 3-O-arabinoside; Kaempferol 3-O-rhamnoside; Kaempferol 3-O-galactoside; Kaempferol 3-O-glucoside; Isorhamnetin 3-O-rhamnoside; Isorhamnetin 3-O-glucoside[11,43]
      Mulberry
      		Quercetin 3-O-rutinoside; Kaempferol 3-O-glucoside; Quercetin 3-O-glucoside; Quercetin 3-O-rhamnoside; Quercetin 3-O-galactoside; Quercetin 3-O-glucuronide; Quercetin; Myricetin 3-O-rhamnoside; Isorhamnetin 3-O-glucoside; Myricetin; Kaempferol; Isorhamnetin; Fisetin; Morin; Rhamnetin; Galangin; Kaempferide[17]
      Strawberry
      		Quercetin glucuronide; Quercetin pentoside; Kaempferol coumaroylhexoside; Quercetin 3-O-glucoside; Quercetin 7-O-glucoside; Quercetin 4’-O-glucoside; Kaempferol 3-O-glucoside; Kaempferol 7-O-glucoside; Kaempferol 4’-O-glucoside; Kaempferol glucuronide; Isorhamnetin 3-O-glucoside; Isorhamnetin 7-O-glucoside; Isorhamnetin 4’-O-glucoside; Isorhamnetin glucuronide[24,44]
      Cherry
      		Quercetin 3-O-rutinoside; Kaempferol 3-O-rutinoside; Quercetin 3-O-glucosil-rutinoside; Quercetin 3-O-rhamnoside; Quercetin 3-O-galactoside; Quercetin 3-O-glucoside; Quercetin 3-O-diglucoside; Kaempferol 3-O-glucoside; Kaempferol 3-O-rhamnoside; Isorhamnetin 3-O-rutinoside[45]
      Tomato
      		Quercetin 3-O-rutinoside; Kaempferol 3-O-rutinoside; Quercetin glucosyl-glucoside rhamnoside; Quercetin 3-O-rutinoside-7-O-glucoside; Quercetin 3-O-glucoside; Quercetin 3,7-O-glucoside; Kaempferol glucosyl-glucoside rhamnoside; Kaempferol 3-O-glucoside; Kaempferol 3,7-O-glucoside; Kaempferol 3-O-rutinoside-7-O-glucoside[46,47,48]
      Mango
      		Quercetin 3-O-galactoside; Quercetin 3-O-glucoside; Quercetin 3-O-xyloside; Quercetin diglycoside; Quercetin 3-O-arabinopyranoside; Quercetin 3-O-arabinofuranoside; Quercetin 3-O-rhamnoside; Rhamnetin 3-O-galactoside; Rhamnetin 3-O-glucoside; Rhamnetin 3-O-galactopyranoside; Rhamnetin 3-O-glucopyranoside; Kaempferol 3-O-glucoside; Quercetin; Isorhamnetin 3-O-glucoside[26]
      Litchi
      		Quercetin rhamnosyl-rutinoside; Quercetin 3-O-rutinoside; Isorhamnetin rhamnosyl-rutinoside; Quercetin rhamnosyl-glucoside; Isomer of Quercetin rhamnosyl-glucoside; Quercetin 3-O-rutinoside-O-rhamnoside; Quercetin glucosyl-rutinoside; Quercetin rhamnosyl-glucosyl-rutinoside; Kaempferol rhamnosyl-rutinoside; Kaempferol 3-O-rutinoside-O-rhamnoside; Kaempferol 3-O-rutinoside; Keampferol rhamnosyl-glucosyl-rutinoside; Isorhamnetin 3-O-rutinoside; Isorhamnetin 3-O-rutinoside-O-rhamnoside; Isorhamnetin glucosyl-rutinoside; Myricetin rutinoside[49,50]
      Citrus
      		Quercetin 3-O-glucoside; Quercetin 3-O-rutinoside; Quercetin 7-O-glucoside; Quercetin 7-O-rutinoside; Quercetin 3-O-glucofuranoside; Kaempferol 3-O-glucoside; Kaempferol 3-O-rutinoside; Kaempferol 7-O-glucoside; Kaempferol 7-O-rutinoside[51,52]
      Kiwi fruit
      		Quercetin 3-O-rutinoside; Quercetin 3-O-glucoside; Kaempferol 3-O-rutinoside;
      Quercetin 3-O-arabinofuranoside; Quercetin 3-O-rhamnoside; Quercetin 4’-O-glucoside; Kaempferol 3-O-galactoside; Kaempferol 3-O-rhamnoside; Kaempferol 3-O-robinobioside; Kaempferol 3,7-O-diglucoside 8-prenyl derivative; Myricetin 3-O-galactoside; Syringetin      		[33]

      Table 2.  Distribution of divergent flavonols in fruits. The first three listed compounds are the major flavonols in each fruit.

    • SpeciesGenesMetabolitesSubgroupReference
      Fragaria ananasaFaMYB1Flavonol, AnthocyaninSG4[76]
      Vitis viniferaVvMYB5aFlavonol, AnthocyaninSG6[84,85]
      VvMYBF1FlavonolSG7[86]
      VvMYB12FlavonolSG7[85]
      VvibZIPC22Flavonol, AnthocyaninbZIPC[81]
      VvMYBA2Flavonol, AnthocyaninSG6[87]
      VvMYB114Flavonol, AnthocyaninUnknown[82]
      Malus domesticaMdMYB3Flavonol, AnthocyaninSG4[78]
      MdMYB22FlavonolSG7[75]
      Malus crabappleMcMYB10Flavonol, AnthocyaninSG6[80]
      MdMYB8FlavonolUnknown[83]
      Pyrus bretschneideriPbMYB9Flavonol, AnthocyaninSG5[79]
      PbMYB12bFlavonolSG7[37]
      PbMYB17FlavonolSG7[36]
      Prunus persicaPpMYB15, PpMYBF1FlavonolSG7[22]
      Morella rubraMrMYB12FlavonolSG7[77]
      Solanum lycopersicumSlMYB12FlavonolSG7[88]
      Citrus sinensisCsMYBF1FlavonolSG7[89]

      Table 3.  Summary of MYB and bZIP transcription factors characterized in a wide range of fruit species regulating flavonol accumulation.