Drought poses a major threat to apple fruit production and quality. Because of the apple’s long juvenile phase, developing varieties with improved drought tolerance using biotechnology approaches is needed. Here, we used the RNAi approach to knock down six GH3 genes in the apple. Under prolonged drought stress, the MdGH3 RNAi plants performed better than wild-type plants and had stronger root systems, higher root-to-shoot ratio, greater hydraulic conductivity, increased photosynthetic capacity, and increased water use efficiency. Moreover, MdGH3 RNAi plants promoted the drought tolerance of scion when they were used as rootstocks, as compared with the wild type and M9-T337 rootstocks. Scion grafted onto the MdGH3 RNAi plants showed increased plant height, stem diameter, photosynthetic capacity, special leaf weight, and water use efficiency. The use of the MdGH3 RNAi plants as rootstocks can also increase the C/N ratio of the scion and achieve the same effect as the M9-T337 rootstock in promoting the flowering and fruiting of the scion. Notably, using MdGH3 RNAi plants as rootstocks did not reduce fruit weight and scion quality compared with using M9-T337 rootstock. Our research provides candidate genes and demonstrates a general approach that could be used to improve the drought tolerance of fruit trees without sacrificing the yield and quality of scion fruits.

中文翻译：

---

通过敲低 6 个 GH3 基因来设计耐旱苹果以及转基因苹果作为砧木的潜在应用

干旱对苹果果实的生产和质量构成重大威胁。由于苹果的幼年期较长，因此需要使用生物技术方法开发具有更高耐旱性的品种。在这里，我们使用 RNAi 方法敲除苹果中的六个 GH3 基因。在长期干旱胁迫下，MdGH3 RNAi 植物比野生型植物表现更好，具有更强的根系、更高的根冠比、更大的水力传导性、增加的光合能力和水分利用效率。此外，与野生型和M9-T337砧木相比，MdGH3 RNAi植物在接穗用作砧木时提高了其耐旱性。嫁接到 MdGH3 RNAi 植物上的接穗显示出增加的株高、茎粗、光合能力、特殊叶重和水分利用效率。使用MdGH3 RNAi植物作为砧木还可以提高接穗的C/N比，在促进接穗开花结果方面达到与M9-T337砧木相同的效果。值得注意的是，与使用 M9-T337 砧木相比，使用 MdGH3 RNAi 植物作为砧木并不会降低果实重量和接穗质量。我们的研究提供了候选基因，并展示了一种通用方法，该方法可用于在不牺牲接穗果实产量和质量的情况下提高果树的耐旱性。