The aim of this work was to evaluate the general role of the vacuolar pyrophosphatase proton pump (V-PPase) in sucrose accumulation in citrus species. First, three citrus V-PPase genes, designated CsVPP-1, CsVPP-2, and CsVPP-4, were identified in the citrus genome. CsVPP-1 and CsVPP-2 belonging to citrus type I V-PPase genes are targeted to the tonoplast, and CsVPP-4 belonging to citrus type II V-PPase genes is located in the Golgi bodies. Moreover, there was a significantly positive correlation between transcript levels of type I V-PPase genes and sucrose, rather than hexose, content in fruits of seven citrus cultivars. Drought and abscisic acid treatments significantly induced the CsVPP-1 and CsVPP-2 transcript levels, as well as the sucrose content. The overexpression of type I V-PPase genes significantly increased PPase activity, decreased pyrophosphate contents, and increased sucrose contents, whereas V-PPase inhibition produced the opposite effect in both citrus fruits and leaves. Furthermore, altering the expression levels of type I V-PPase genes significantly influenced the transcript levels of sucrose transporter genes. Taken together, this study demonstrated that CsVPP-1 and CsVPP-2 play key roles in sucrose storage in the vacuole by regulating pyrophosphate homeostasis, ultimately the sucrose biosynthesis and transcript levels of sucrose transport genes, providing a novel lead for engineering or breeding modified taste in citrus and other fruits.

中文翻译：

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I型H +-焦磷酸酶调节柑橘类水果中蔗糖的液泡储存。

这项工作的目的是评估液泡焦磷酸酶质子泵（V-PPase）在柑桔物种蔗糖积累中的一般作用。首先，在柑橘基因组中鉴定出三个名为CsVPP-1，CsVPP-2和CsVPP-4的柑橘V-PPase基因。属于柑橘I型V-PPase基因的CsVPP-1和CsVPP-2靶向液泡膜，而CsVPP-4属于柑橘II型V-PPase基因的基因位于高尔基体中。此外，在七个柑橘品种的果实中，I型V-PPase基因的转录水平与蔗糖含量而不是己糖含量之间存在显着的正相关。干旱和脱落酸处理显着诱导了CsVPP-1和CsVPP-2转录水平以及蔗糖含量。I型V-PPase基因的过表达显着提高了PPase的活性，降低了焦磷酸盐的含量，并增加了蔗糖的含量，而V-PPase的抑制作用在柑橘类水果和叶片中均产生了相反的作用。此外，改变I型V-PPase基因的表达水平显着影响了蔗糖转运蛋白基因的转录水平。两者合计，这项研究表明CsVPP-1和CsVPP-2通过调节焦磷酸稳态，最终改变蔗糖转运基因的蔗糖生物合成和转录水平，在液泡中的蔗糖储存中发挥关键作用，为工程或育种改良口味提供了新的线索在柑橘和其他水果中。