Figures (2)  Tables (1)

    • Figure 1. 

      The reported vacuolar sugar transporters in fruit crops. (1) Malus domestica sucrose transporters, MdSUT4; (2) Citrus sinensis sucrose transporters, CsSUT4; (3) Beta vulgaris sucrose transporters, BvSUT1; (4) Vitis vinifera tonoplast sugar transporter, VvTMT1 and VvTMT2; (5) Malus domestica tonoplast sugar transporter, MdTMT1 and MdTMT2; (6) Cucumis melo tonoplast sugar transporter, CmTST1 and CmTST2; (7) Pyrus bretschneideri tonoplast sugar transporter, PbTMT4; (8) Citrullus lanatus tonoplast sugar transporter, ClTST2; (9) Beta vulgaris tonoplast sugar transporter, BvTST2.1; (10) Solanum tuberosum tonoplast sugar transporter, StTST3.1; (11) Solanum tuberosum tonoplast sugar transporter, StTST3.2; (12) Prunus persica tonoplast sugar transporter, PpTST1; (13) Fragaria vesca tonoplast sugar transporter, FvTST1; (14) Malus domestica vacuolar glucose transporter, MdVGT1. (15) Malus domestica early response to dehydration-like 6, MdERDL6-1; (16) Citrus sinensis sugars will eventually be exported transporter, CsSWEET16.

    • Figure 2. 

      The reported vacuolar acid transporters and proton pumps in fruit crops. (1) Vitis vinifera aluminum-activated malate channel protein, VvALMT9; (2) Malus domestica V-ATPase (vacuolar H+-ATPase, abbreviated VHA), MdVHA-A; (3) Malus domestica V-PPase (vacuolar H+-pyrophosphatase, abbreviated VHP), MdVHP1; (4) Citrus sinensis citrate transporter 1, CsCit1; (5) Malus domestica aluminum-activated malate channel protein, MdALMT9; (6) Ziziphus jujuba aluminum-activated malate channel protein, ZjALMT4;(7) Solanum lycopersicum aluminum-activated malate channel protein, SlALMT5;(8) Solanum lycopersicum aluminum-activated malate channel protein, SlALMT9; (9) Solanum lycopersicum tonoplast dicarboxylic transporter, SlTDT1; (10) Malus domestica tonoplast dicarboxylic transporter, MdTDT1; (11) Malus domestica P-type ATPases, MdPH1 and MdPH5; (12) Citrus sinensis P-type ATPases, CsPH1 and CsPH5; (13) Citrus sinensis V-ATPase (vacuolar H+-ATPase, abbreviated VHA), MdVHA-A.

    • ProteinsSpeciesFunctionsReference
      VvALMT9Vitis vinifera L.(grape)Unidirectional transport of malic acid and tartaric acid to vacuoles.[56]
      MdALMT9Malus domestica Borkh. (apple)WRKY31-ERF72-MA1 network regulates malic acid accumulation in apple fruit.[84]
      Ma1Malus domestica (apple)ma1 reduces its malic acid transport function by removing the conservative C-terminal domain of MA1, resulting in low acidity of apple fruit.[59][54]
      ZjALMT4Ziziphus jujuba Mill.(jujube)ZjWRKY7 activates the expression of ZjALMT4 to promote the accumulation of malate.[85]
      SlALMT5Solanum lycopersicum (tomato)The SLALMT5 transported malate and inorganic anions such as nitrate and chloride, but not citrate.[56]
      SlALMT9Solanum lycopersicum (tomato)SlALMT9 can determine the malic acid content and aluminum tolerance of tomato.[57]
      SlTDTSolanum lycopersicum (tomato)The overexpression of SlTDT significantly increased the content of malic acid in tomato fruit and decreased the content of citric acid.[50]
      MdTDT1Malus domestica Borkh. (apple)MdMYB1 can affect the expression of acid transporters Ma1 and MdtDT to regulate fruit acidity.[86]
      CsCit1Citrus sinensis. cv WashingtonCsCit1mediates CitH2- and CitH2--dependent H+ efflux from the vacuole and maintains vacuolar acidic pH and citric acid homeostasis.[62]
      DsSWEET17Dianthus spiculifolius (caryophyllus)Influence on sugar metabolism and tolerance to stress in Arabidopsis thaliana.[87]
      MdSUT4Malus domestica (apple)MdSUT4 may participate in the efflux of sucrose from the vacuolar membrane and may promote the synthesis of flavonoids.[28]
      CsSUT4Citrus sinensis (citrus)In the natural state, CsSUT4 mainly mediates the output of sucrose in vacuoles.[29]
      BvSUT1Beta vulgaris L.(sugar beet)BvSUT1 is a sucrose transport protein responsible for transporting sucrose to the main root of sugar beet.[26]
      VvTMT1Vitis vinifera L.(grape)VvTMT1 participates in vacuolar monosaccharide transport and plays a major role in stress response.[88]
      VvTMT2Vitis vinifera L.(grape)VvTMT2 gene is involved in the transport of hexose from cytoplasm to vacuole during berry ripening and over-ripening.[89]
      MdTMT1 and MdTMT2Malus domestica Borkh. (apple)MdTMT1 and MdTMT2 are involved in the accumulation of fructose and sucrose during apple fruit ripening.[90]
      CmTST2Cucumis melo L.(melon)CmTST2 plays an important role in sugar accumulation of melon fruit.[38]
      CmTST1Cucumis melo L.(melon)CmTST1 transports sugar into vacuoles.[33]
      PbTMT4Pyrus bretschneideri (pear)PbTMT4 participates in the sugar accumulation of vacuoles, thus affecting the growth and development of plants.[35]
      ClTST2Citrullus lanatus (watermelon)ClTST2 encodes a vacuolar membrane protein, and its expression is related to the uptake and accumulation of vacuolar membrane sugar in watermelon pulp cells.[37]
      BvTST2.1Beta vulgaris L.(sugar beet)The transporter BvTST2.1 is responsible for the uptake of vacuole sucrose in beet taproots.[40]
      PpTST1Prunus persica L. (peach)Overexpression of PpTST1 led to a decrease in organic acid content and an increase in sugar content in peach and tomato fruits, indicating that it has dual functions in sugar accumulation and organic acid content.[39,91]
      StTST3.1Solanum tuberosum L. (potato)StTST3.1-silenced leaves accumulated exceptionally high levels of maltose but low levels of sucrose and hexose.[92]
      StTST3.2Solanum tuberosum L. (potato)Silencing of StTST3.2 in potato by stable transformation resulted in significantly lower RS content in tubers at harvest or after room temperature storage.[93]
      FvTST1Fragaria vesca L. (strawberry)FvTST1 can mediate the uptake of different sugars, such as fructose, glucose, sucrose, and mannose.[94]
      MdVGT1Malus domestica Borkh. (apple)MdVGT1 and MdTMT1 interact to transport glucose into vacuole.[95]
      MdERDL6-1Malus domestica Borkh. (apple)MdERDL6-1 is a vacuole membrane H+/glucose co-transporter.[31]
      CsERD6LCitrus sinensis (citrus)The function of CsERD6L was verified to have glucose transport activity.[29]
      LeVHA-AP1Lycopersicon esculentum L. (tomato)The concentration of sucrose in fruit of antisense transgenic tomato with V-ATPase A subunit was increased, but the concentration of glucose and fructose did not change.[71]
      MdVHA-AMalus domestica Borkh. (apple)MdVHA-A was involved in malate accumulation and vacuolar acidification in apple.[70]
      CitVHA-c4C. reticulata Blanco cv. PonkanCitVHA-c4 was reported to be involved in citric acid accumulation.[68]
      MdVHP1Malus domestica Borkh. (apple)Overexpression or heterologous expression of V-PPase coding gene MdVHP1 significantly promoted the accumulation of malic acid in apple callus and tomato fruit.[96]
      MdPH1 and MdPH5Malus domestica Borkh. (apple)MdPH1 and MdPH5 have been identified and shown to be involved in vacuolaracidification and malate accumulation[70]
      CitPH1 and CitPH5Citrus sinensis. Cv WashingtonCitPH1 and CitPH5, are expressed in the fruits of sour lemon, orange, pummelo, and rangpur lime.[77]
      Ma10Malus domestica (apple)Ma10 gene encodes P3A H+- ATPase of the vacuolar membrane that controls the vacuolar acidification of apple fruit.[55]

      Table 1. 

      The reported vacuolar membrane proteins involved in sugar and acid accumulation in fruit crops.