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Figure 1.
Sugar metabolism and accumulation in apple fruit. In apples, both sorbitol (Sor) and sucrose (Suc) are transported from photosynthetic cells to the sieve element/ companion cell (SE-CC) complex in fruit, then unloaded into the cell wall space between SE-CC and parenchyma cells by unknown transporters. In cell wall space, Sor is taken up into parenchyma cells by sorbitol transporter (SOT). Suc is directly transported into parenchyma cells by sucrose transporter/carrier (SUT/SUC), or converted to fructose (Fru) and glucose (Glc) in the cell wall space by cell wall invertase (CWINV), and then transported into the parenchyma cells by hexose transporters (HT). After entering into the cytoplasm, Sor is converted to Fru by sorbitol dehydrogenase (SDH), while Suc is converted to Fru and Glc by neutral invertase (NINV) or to Fru and UDP-glucose by sucrose synthase (SUSY). The produced Fru and Glc can be phosphorylated to fructose-6-P (F6P) and gluctose-6-P (G6P) by fructokinase (FRK) or hexose kinase (HxK). The resulting G6P, F6P, G1P and UDPG enter glycolysis/TCA cycle, or are used for starch synthesis or other metabolic processes. Exceeded UDPG could be combined with F6P for re-synthesis of Suc via sucrose phosphate synthase (SPS) and sucrose-phosphatase (SPP). Most of the Fru, Glc and Suc that have not been metabolized are imported by special tonoplast transporters (including tonoplast sugar transporter, TST, SUC4, or SWEET) into vacuole for storage. Inside the vacuole, Suc can be also converted to Glc and Fru by acid invertase (AINV). In addition, the Glc in the vacuole could be transported to the cytoplasm by the Glc exporter early response to dehydration like 6 (ERDL6) protein.
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Chromosome Localization (cM) Reference Hybrid population Brix/SSC Fructose Glucose Sucrose Sorbitol LOD score/ Bayes factor Peoportion of phenotypic variation explained by QTLs Notes LG01 59.8−85.7 cM/ 59.8−76.3 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 32.2/31.1 34%/45% 60.9−76.3 cM/ 61.1−85.7 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 11.4/11.1 22%/19% 54.6−76.3 cM/ 60.9−76.3 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 9.7/33.0 17%/36% 62.9−85.7 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 10.4 21% 32.81−42.74 cM Sun et al. (2015)[50] 'Jonathan' × 'Golden Delicious' √ LOD 4.3 ('Jonathan') 28.5% ('Jonathan') 48.60−50.57 cM Sun et al. (2015)[50] 'Jonathan' × 'Golden Delicious' √ LOD 3.5 ('Golden Delicious') 17.5% ('Golden Delicious') / Liao et al. (2021)[64] 497 Malus accessions √ / / / Liao et al. (2021)[64] 497 Malus accessions √ / / 95.51−97.97 cM/ 113.14−116.40 cM/
97.67−95.00 cM/112.45−123.09 cM/
47.25−49.39 cM/ 86.85−93.56 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.29/4.71/3.00/4.14 ('Honeycrisp'); LOD 3.46/3.60 ('Qinguan') 12.5%/17.5%/13.5%/18.2% ('Honeycrisp'); 15.4%/16.0% ('Qinguan') LG02 / Kenis et al. (2008)[61] 'Telamon' ×'Braeburn' √ LOD 3.3/ 3.8 ('Telamon');
LOD 3.4/4.0 ('Braeburn')6.5%/8.0% ('Telamon');
7.4%/8.1% ('Braeburn')75.8−84.4 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 3.2 6% 1.2−12.8 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 7.2 13% QTLs after 20 weeks of refrigerated storage 51.08−56.67 cM/ 10.20−21.00 cM Wang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.42 ('Honeycrisp');
LOD 3.80 ('Qinguan')15.3% ('Honeycrisp');
14.4% ('Qinguan')LG03 / Liebhard et al. (2003)[36] 'Fiesta' × 'Discovery' √ LOD 2.0 ('Fiesta') 5% ('Fiesta') 28.8−38.0 cM/54.0−77.2 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 3.3/10.6 3%/22% 14.2−28.9 cM/5.0−13.5 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 5.4/9.2 10%/15% 54.0−71.3 cM/73.3−87.0 cM/
49.2−69.3 cMGuan et al. (2015)[21] 274 representative germplasm √ BF 4.8/10.2/9.6 7%/26%/23% QTLs after 10 weeks /20 weeks/10 weeks of refrigerated storage 5.0−25.2 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 6.7 10% QTLs after 20 weeks of refrigerated storage 49.2−69.3 cM/73.3−87.0 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 11.3/3.9 22%/5% QTLs after 10 weeks/20 weeks of refrigerated storage 34.94−69.34 cM Ma et al. (2016)[17] 'Jiguan' × 'Wangshanhong' √ LOD 5.75 ('Wangshanhong') 20.6% ('Wangshanhong') 38.06−60.34 cM Ma et al. (2016)[17] 'Jiguan' × 'Wangshanhong' √ LOD 4.47 ('Wangshanhong') 17.1% ('Wangshanhong') 45.47−58.34 cM Ma et al. (2016)[17] 'Jiguan' × 'Wangshanhong' √ LOD 3.41 ('Wangshanhong') 11.7% ('Wangshanhong') 34.94−90.29 cM Ma et al. (2016)[17] 'Jiguan' × 'Wangshanhong' √ LOD 7.73 ('Wangshanhong') 28.0% ('Wangshanhong') / Liao et al. (2021)[64] 497 Malus accessions √ / / 19.93−23.31 cM/ 20.95−23.31 cM/
73.86−76.66 cM/ 14.39−19.69 cM/
24.77−32.25 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.31/3.28/3.18 ('Honeycrisp'); LOD 3.47/4.52 ('Qinguan') 12.6%/14.7%/14.3% ('Honeycrisp'); 13.2%/16.8% ('Qinguan') LG04 7.9−16.1 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 7.4 8% 28.77−0.37 cM Ma et al. (2016)[17] 'Jiguan' × 'Wangshanhong' √ LOD 4.49 ('Wangshanhong') 16.7% ('Wangshanhong') 30.08−30.72 cM/ 37.09−37.79 cM/
44.60−45.53 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.42/3.38/3.26 ('Qinguan') 13.0%/12.9%/12.4% ('Qinguan') LG05 / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.34 ('Akane') 12.4% ('Akane') 3.2−10.8 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 2.3 2% LG06 / Liebhard et al. (2003)[36] 'Fiesta' × 'Discovery' √ LOD 4.9 ('Fiesta');
LOD 4.2 ('Discovery')17% ('Fiesta');
15% ('Discovery')/ Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.27 ('Akane') 10.9% ('Akane') / Costa F (2015)[62] 'Fuji' × 'Delearly', 'Fuji' × 'Cripps Pink_Pink Lady', 'Golden Delicious' × 'Scarlet', and 'Golden Delicious' × 'Braeburn' √ / / LG07 / Liao et al. (2021)[64] 497 Malus accessions √ / / 64.33−78.37 cM/ 84.51−116.22 cM/
128.14−134.43 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.74/3.98/3.62 ('Honeycrisp') 14.1%/15.0%/13.7% ('Honeycrisp') LG08 / Liebhard et al. (2003)[60] 'Fiesta' × 'Discovery' √ LOD 1.9 ('Discovery') 4% ('Discovery') / Costa F (2015)[62] 'Fuji' × 'Delearly', 'Fuji' × 'Cripps Pink_Pink Lady', 'Golden Delicious' × 'Scarlet', and 'Golden Delicious' × 'Braeburn' √ / / 10.57−14.54 cM/ 32.37−49.38 cM/
57.76−62.73 cM/ 71.73−74.36 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.96/16.6/15.7/15.7 ('Qinguan') 14.9%/16.6%/15.7%/15.7% ('Qinguan') LG09 / Liebhard et al. (2003)[36] 'Fiesta' × 'Discovery' √ LOD 3.3 ('Discovery') 7% ('Discovery') 0.7−19.6 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 6.4 24% 40.2−49.1 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 2.1 1% / Liao et al. (2021)[64] 497 Malus accessions √ / / LG10 / Kenis et al. (2008)[61] 'Telamon' ×'Braeburn' √ LOD 5.8/12.4 ('Telamon');
LOD 3.7/12.6 ('Braeburn')12.4%/30.1% ('Telamon');
9.0%/29.3% ('Braeburn')/ Kenis et al. (2008)[61] 'Telamon' ×'Braeburn' √ LOD 8.5 ('Telamon');
LOD 8.9 ('Braeburn')19.5% ('Telamon');
20.6% ('Braeburn')/ Liao et al. (2021)[64] 497 Malus accessions √ / / 23.9−28.45 cM/ 36.36−38.23 cM/
25.66−27.27 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 4.24/3.43 ('Honeycrisp');
LOD 3.15 ('Qinguan')15.9%/13.0% ('Honeycrisp');
12.1% ('Qinguan')LG11 39.2−57.5 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 4.7 7% / Liao et al. (2021)[64] 497 Malus accessions √ / / 49.95−50.72 cM Wang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.02 ('Qinguan') 11.6% ('Qinguan') LG12 / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 2.79 ('Orin') 10.5% ('Orin') 41.5−48.3 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 5.3 12% QTLs after 10 weeks of refrigerated storage / Costa F (2015)[62] 'Fuji' × 'Delearly', 'Fuji' × 'Cripps Pink_Pink Lady', 'Golden Delicious' × 'Scarlet', and 'Golden Delicious' × 'Braeburn' √ / / 34.53−39.20 cM/ 69.64−72.66 cM/
99.01−104.04 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 4.37 ('Honeycrisp');
LOD 3.29/3.32 ('Qinguan')16.3% ('Honeycrisp');
14.7%/14.9% ('Qinguan')LG13 54.2−71.5 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 3.1 7% 99.8−162.8 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 5.6 27% QTLs after 20 weeks of refrigerated storage 36.64−38.77 cM/ 47.21−47.62 cM/ 86.29−94.41cM Wang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.99 ('Honeycrisp');
LOD 3.43/3.47 ('Qinguan')15.0% ('Honeycrisp');
13.1%/15.5% ('Qinguan')LG14 / Liebhard et al. (2003)[36] 'Fiesta' × 'Discovery' √ LOD 4.2 ('Fiesta');
LOD 3.3 ('Discovery')11% ('Fiesta');
7% ('Discovery')22.59−25.67 cM/ 55.87−56.63 cM Wang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.20 ('Honeycrisp');
LOD 3.39 ('Qinguan')12.2% ('Honeycrisp');
12.9% ('Qinguan')LG15 / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 4.88 ('Orin') 13.2% ('Orin') / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.06 ('Akane') 10.1% ('Akane') 75.8−77.1 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 4.9 10% 94.7−104.3 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 4.4 5% 31.7−38.4 cM/ 34.1−40.3 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 4.7/5.6 17%/13% QTLs after 20 weeks/10 weeks of refrigerated storage 94.7−99.5 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 5.4 12% QTLs after 10 weeks of refrigerated storage LG16 / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 8.26 ('Orin') 22.5% ('Orin') / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.03 ('Akane') 10.2% ('Akane') / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.00 ('Akane') 10.0% ('Akane') / Kunihisa et al. (2014)[22] 'Orin' × 'Akane' √ LOD 3.74 ('Akane') 13.8% ('Akane') 2.4−8.8 cM Guan et al. (2015)[21] 274 representative germplasm √ BF 4.2 6% 65.35−70.60 cM/ 98.75−91.75 cM/
17.71−29.61 cM/35.81−37.07 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.25/3.18 ('Honeycrisp');
LOD 3.45/3.31 ('Qinguan')12.4%/12.2% ('Honeycrisp');
13.1%/12.6% ('Qinguan')LG17 74.02−75.17 cM/ 85.49−86.03 cM/
73.21−74.18 cMWang et al. (2022)[18] 'Honeycrisp' × 'Qinguan' √ LOD 3.65/3.44/3.59 ('Qinguan') 13.8%/13.1%/16.0 ('Qinguan') Table 1.
QTL analysis of sugar content in apples.
Figures
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Tables
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