Overexpression of the RNA binding protein MhYTP1 in transgenic apple enhances drought tolerance and WUE by improving ABA level under drought condition

MhYTP1 is involved in post-transcriptional regulation as a member of YT521-homology (YTH) domain-containing RNA-binding proteins. We previously cloned MhYTP1 and found it participated in various biotic and abiotic stress responses. However, its function in long-term moderate drought has not been verified. Thus, we explored its biological role in response to drought. Under drought condition, the net photosynthesis rate (P-n) and water use efficiency (WUE) were significantly elevated in MhYTP1-overexpressing (OE) apple plants when compared with the non-transgenic (NT) controls. Further analysis indicated MhYTP1 expression was associated with elevated ABA content, increased stomatal density and reduced stomata! aperture. In addition, to gain insight into the function of stem-specific expression of MhYTP1, grafting experiments were performed. Interestingly, lower transpiration rate (T-r) and higher WUE were observed when transgenic plants were used as scions as opposed to rootstocks and when transgenic rather than NT plants were used as rootstocks, indicating MhYTP1 plays crucial roles in grafted plants. These results define a function for MhYTP1 in promoting tolerance to drought conditions, and suggest that MhYTP1 can serve as a candidate gene for future apple drought resistance breeding with the help of biotechnology.