The accumulation of soluble sugars in fleshy fruits largely determines their sweetness or taste. A spontaneous sweet orange mutant 'Hong Anliu' (HAL, Citrus sinensis) accumulates low soluble sugar content in fruit juice sacs than its wild type, 'Anliu' (AL) orange; however, the cause of reduced sugar content in 'HAL' fruit remains unclear. In this study, sugar content and expression profiles of genes involved in sugar metabolism and transport were compared between 'HAL' and 'AL' fruit juice sacs. In both cultivars, fructose and glucose displayed the increasing trends with significantly lower contents in 'HAL' than 'AL' after 160 DAF; moreover, sucrose had a declining trend in 'HAL' and increasing trend in 'AL' with fruit development. On the other hand, transcript levels of VINV, CWINV1, CWINV2, SUS4, SUS5, SPS1, SPS2, VPP-1, VPP-2, and some sugar transporter genes were significantly decreased in 'HAL' compared with 'AL' after 100 DAF or 160 DAF. Interestingly, the transcript levels of SPS2 and SUT2 exhibited a similar trend as it was found for sucrose content in both cultivars. These results suggested that the low sugar accumulation in 'HAL' fruit JS is accompanied by the reduced sink strength, sucrose-synthesis ability, and vacuolar storage ability compared with 'AL'; reduction of CWINVs, VINV, SPS2, SUT2, VPP-1, and VPP-2 transcript levels possibly plays a key role in the low storage of soluble sugars in the vacuoles of mutant juice sacs.

中文翻译：

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糖和糖积累相关基因表达谱的评估揭示了甜橙（柑橘）芽突变体中低糖积累性状形成的新见识。

肉质水果中可溶性糖的积累在很大程度上决定了其甜度或口味。自发的甜橙突变体“洪安流”（HAL，柑桔）在果汁囊中的可溶性糖含量比野生型“安流”橙低。但是，“ HAL”水果中糖含量降低的原因仍不清楚。在这项研究中，糖含量和参与糖代谢和运输的基因的表达谱进行了比较，在'HAL'和'AL'果汁囊之间。在两个品种中，果糖和葡萄糖均显示出增加的趋势，在160 DAF后，“ HAL”中的果糖含量明显低于“ AL”。此外，随着果实的发育，蔗糖的“ HAL”含量呈下降趋势，而“ AL”含量呈上升趋势。另一方面，100 DAF或160 DAF后，与“ AL”相比，“ HAL”中VINV，CWINV1，CWINV2，SUS4，SUS5，SPS1，SPS2，VPP-1，VPP-2和某些糖转运蛋白基因的转录水平显着降低。有趣的是，SPS2和SUT2的转录水平呈现出与两个品种中蔗糖含量相似的趋势。这些结果表明，与'AL'相比，'HAL'果实JS中的低糖积累伴随着降低的沉陷强度，蔗糖合成能力和液泡贮藏能力。降低CWINVs，VINV，SPS2，SUT2，VPP-1和VPP-2转录水平可能在突变汁囊液泡中可溶性糖的低存储中起关键作用。HAL”与100 DAF或160 DAF后的“ AL”相比。有趣的是，SPS2和SUT2的转录水平呈现出与两个品种中蔗糖含量相似的趋势。这些结果表明，与'AL'相比，'HAL'果实JS中的低糖积累伴随着降低的沉陷强度，蔗糖合成能力和液泡贮藏能力。降低CWINVs，VINV，SPS2，SUT2，VPP-1和VPP-2转录水平可能在突变汁囊液泡中可溶性糖的低存储中起关键作用。HAL”与100 DAF或160 DAF后的“ AL”相比。有趣的是，SPS2和SUT2的转录水平呈现出与两个品种中蔗糖含量相似的趋势。这些结果表明，与'AL'相比，'HAL'果实JS中的低糖积累伴随着降低的沉陷强度，蔗糖合成能力和液泡贮藏能力。降低CWINVs，VINV，SPS2，SUT2，VPP-1和VPP-2转录水平可能在突变汁囊液泡中可溶性糖的低存储中起关键作用。与“ AL”相比，果实JS具有降低的沉陷强度，蔗糖合成能力和液泡贮藏能力。降低CWINVs，VINV，SPS2，SUT2，VPP-1和VPP-2转录水平可能在突变汁囊液泡中可溶性糖的低存储中起关键作用。与“ AL”相比，果实JS具有降低的沉陷强度，蔗糖合成能力和液泡贮藏能力。降低CWINVs，VINV，SPS2，SUT2，VPP-1和VPP-2转录水平可能在突变汁囊液泡中可溶性糖的低存储中起关键作用。