MdTyDc Overexpression Improves Alkalinity Tolerance in Malus domestica

Abstract

Tyrosine is decarboxylated to tyramine by TYDC (Tyrosine decarboxylase) and then hydroxylated to dopamine, which is involved in plant response to abiotic stress. However, little is known about the function of <i>MdTyDc</i> in response to alkaline stress in plants. In our study, it was found that the expression of <i>MdTyDc</i> was induced by alkaline stress. Therefore, the apple plants overexpressing <i>MdTyDc</i> was treated with alkali stress, and we found that <i>MdTyDc</i> played an important role in apple plants' resistance to alkali stress. Our results showed that the restriction on the growth, the decrease of membrane permeability and the accumulation of Na⁺ were alleviated to various degrees in <i>MdTyDc</i> transgenic plants under alkali stress. In addition, overexpression of <i>MdTyDc</i> enhanced the root activity and photosynthetic capacity, and improved the enzyme activity related to N metabolism, thus promoting N absorption. It is noteworthy that the dopamine content of these three transgenic lines is significantly higher than that of WT. In summary, these findings indicated that <i>MdTyDc</i> may enhance alkaline tolerance of apples by mediating dopamine content, mainly by maintaining high photosynthetic capacity, normal ion homeostasis and strong nitrogen absorption capacity.