Overexpression of Tyrosine Decarboxylase (mdtydc) Enhances Drought Tolerance in Malus Domestica

Dopamine is produced in plants and plays a vital role in improving plant responses to abiotic stress. Tyrosine decarboxylase (TYDC) synthesizes tyramine from tyrosine, thereby providing the substrate for dopamine production. However, the function of TYDC in response to drought stress in apple plants remains unclear. In this study, transgenic apple plants that overexpressed MdTYDC were exposed to drought, in order to explore the biological function of TYDC in drought stress. Overexpression of MdTYDC significantly increased apple dopamine content. Transgenic apple plants that overexpressed MdTYDC exhibited less electrolyte leakage, a lower water loss rate, higher photosynthetic pigment contents, and enhanced photosynthetic performance under drought conditions. MdTYDC overexpression also improved reducing power by increasing the ratios of ascorbate to dehydroascorbate and reduced to oxidized glutathione. It influenced leaf water retention capacity and stomatal movement by modulating cellular abscisic acid (ABA) levels and ABA sensitivity. Transcriptomic analyses indicated that MdTYDC overexpression enhanced drought tolerance by regulating the expression of ABA- and drought-related transcription factors, including those from the NAC, ERF, and WRKY families. These results provide evidence for the involvement of MdTYDC and dopamine in enhancing the drought tolerance of apple plants.