Fruit skin color is an important characteristic of fruit quality. The light-mediated regulation on fruit skin coloration in Actinidia arguta remains unclear. To better understand the role of light in fruit skin coloration, we performed bagging treatments in both on-tree and off-tree ‘Hongbaoshixing’, which is a kind of all-red-typed A. arguta cultivar. Non-bagging kiwifruits were used as control. For off-tree fruits, there was no difference between non-bagging and bagging treatments. For on-tree fruits, physiological and molecular changes were investigated during fruit development in non-bagging and bagging treatments. Phenotypic identification and the hue angle measurement showed that the stage of most significant color difference between non-bagging and bagging treatments was 130 days (after full bloom). Determination of five anthocyanin components suggested cyanidin-3-O-galactoside and cyanidin-3-O-xylose-galactoside made a main contribution to the fruit skin coloration. Gene expression profiles and cluster analysis showed AaLDOX and AaUFGT were highly expressed at 130 days and obviously clustered into the same class in non-bagging treatment, respectively. Correlation analysis suggested only AaLDOX expression was significantly correlated with anthocyanin content in non-bagging treatment while no correlation in bagging treatment. Similar results was observed for MYB1 transcription factor. The result of subcellular localization showed that AaLDOX was located in the cytoplasm, indicating AaLDOX is indeed structural gene that encodes leucoanthocyanidin dioxygenase participated in anthocyanin biosynthesis. All results were used to establish a possible working model, showing that light is indispensable for normal fruit skin coloration, and bagging treatment suppresses anthocyanin biosynthesis and accumulation mainly by inhibiting AaMYB1 and AaLDOX expression in A. arguta.

中文翻译：

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套袋对树上猕猴桃（Actinidia arguta）果实表皮着色的限制

果皮颜色是果实品质的重要特征。光介导对猕猴桃果皮着色的调节仍不清楚。为了更好地了解光在果实表皮着色中的作用，我们对树上和树外的“红宝十星”进行了套袋处理，这是一种全红色的 A. arguta 品种。非袋装猕猴桃用作对照。对于树外果实，不套袋和套袋处理之间没有区别。对于树上果实，研究了非套袋和套袋处理果实发育过程中的生理和分子变化。表型鉴定和色调角测量表明，非套袋和套袋处理之间色差最显着的阶段是 130 天（盛开后）。五种花青素成分的测定表明，花青素-3-O-半乳糖苷和花青素-3-O-木糖-半乳糖苷对果皮着色起主要作用。基因表达谱和聚类分析表明，AaLDOX和AaUFGT在130天时高表达，在非装袋处理中分别明显聚类为同一类。相关性分析表明，在非套袋处理中只有AaLDOX的表达与花青素含量显着相关，而在套袋处理中没有相关性。对于 MYB1 转录因子观察到类似的结果。亚细胞定位结果表明AaLDOX位于细胞质中，说明AaLDOX确实是编码参与花青素生物合成的无色花青素双加氧酶的结构基因。