**5. Conclusions**

The present experiment has identified that the apple genome harbors 42 genes encoding putative AQPs. It is necessary for the future to comprehensively understand the process of water and small solutes flues through the membrane and related molecular-regulating mechanisms in the apple tree. In *A. thaliana,* plants were engineered to heterologously express one of these genes (*MpPIP2;1*), a gene which is strongly transcribed in the root of *M. prunifolia*. The transgenic plants exhibited an improved level of tolerance to both drought and salinity stress, which implies that in the apple, the product of *PIP2;1* is an important component of the plant's response to moisture stress. This latter finding suggests a strategy for enhancing the stress tolerance of the apple using a molecular approach.

**Author Contributions:** Conceptualization, J.L.; data curation, J.L.; methodology, H.L. and L.Y.; project administration, F.M.; writing—original draft, M.X.; writing—review & editing, J.L.

**Funding:** This work was supported by the National Natural Science Foundation of China (31401839).

**Conflicts of Interest:** The authors declare no conflict of interest.

## **Abbreviations**


## **References**


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