Soluble sugars are not only an important contributor to fruit quality, but also serve as the osmotic regulators in response to abiotic stresses. Early drought stress promotes sugar accumulation, while specific sugar transporters govern the cellular distribution of the sugars. Here, we show that apple plantlets accumulate soluble sugars in leaf tissues under drought stress. Transcriptional profiling of stressed and control plantlets revealed differential expression of several plasma membrane—or vacuolar membrane-localized sugar transporter genes. Among these, four previously identified vacuolar sugar transporter (VST) genes (MdERDL6–1, MdERDL6–2, MdTST1, and MdTST2) showed higher expression under drought, suggesting their roles in response to drought stress. Promoter cis-elements analyses, yeast one-hybrid, and dual-luciferase tests confirmed that the drought-induced transcription factor MdDREB2A could promote the expression of MdERDL6–1/−2 and MdTST1/2 by binding to their promoter regions. Moreover, overexpressing of each of these four MdVSTs alone in transgenic apple or Arabidopsis plants accumulated more soluble sugars and abscisic acid (ABA), and enhanced drought resistance. Furthermore, apple plants overexpressing MdERDL6–1 also showed reduced water potential, facilitated stomatal closure, and reactive oxygen species scavenging under drought conditions compared to control plants. Overall, our results suggest a potential strategy to enhance drought resistance and sugar accumulation in fruits through manipulating the genes involved in vacuolar sugar transport.

中文翻译：

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受 MdDREB2A 调控的苹果液泡糖转运蛋白通过促进可溶性糖的积累和激活 ABA 信号传导来增强抗旱性


可溶性糖不仅是水果品质的重要贡献者，而且还是响应非生物胁迫的渗透调节剂。早期干旱胁迫促进糖的积累，而特定的糖转运蛋白控制糖的细胞分布。在这里，我们表明苹果植株在干旱胁迫下会在叶片组织中积累可溶性糖。应激植株和对照植株的转录分析揭示了几种质膜或液泡膜定位的糖转运蛋白基因的差异表达。其中，四个先前鉴定的液泡糖转运蛋白 （VST） 基因 （MdERDL6-1、MdERDL6-2、MdTST1 和 MdTST2） 在干旱下表现出更高的表达，表明它们在响应干旱胁迫中的作用。启动子顺式元件分析、酵母单杂交和双荧光素酶测试证实，干旱诱导的转录因子 MdDREB2A 可以通过结合其启动子区域来促进 MdERDL6-1/-2 和 MdTST1/2 的表达。此外，在转基因苹果或拟南芥植株中单独过表达这四种 MdVSTs 中的每一种都积累了更多的可溶性糖和脱落酸 （ABA），并增强了抗旱性。此外，与对照植物相比，过表达 MdERDL6-1 的苹果植物在干旱条件下也显示出水势降低，促进了气孔关闭和活性氧清除。总体而言，我们的研究结果提出了一种通过操纵参与液泡糖运输的基因来增强水果抗旱性和糖分积累的潜在策略。