Zinc finger proteins are widely involved and play an important role in plant growth and abiotic stress. In this research, MdZAT5, a gene encoding C2H2-type zinc finger protein, was cloned and investigated. The MdZAT5 was highly expressed in flower tissues by qRT-PCR analyses and GUS staining. Promoter analysis showed that MdZAT5 contained multiple response elements, and the expression levels of MdZAT5 were induced by various abiotic stress treatments. Overexpression of MdZAT5 in apple calli positively regulated anthocyanin accumulation by activating the expressions of anthocyanin biosynthesis-related genes. Overexpression of MdZAT5 in Arabidopsis also enhanced the accumulation of anthocyanin. In addition, MdZAT5 increased the sensitivity to salt stress in apple calli. Ectopic expression of MdZAT5 in Arabidopsis reduced the expression of salt-stress-related genes (AtNHX1 and AtABI1) and improved the sensitivity to salt stress. In conclusion, these results suggest that MdZAT5 plays a positive regulatory role in anthocyanin accumulation and negatively regulates salt resistance.

Various abiotic stresses, particularly salinization, restrict plant growth and yield around the world. Lipoxygenases play essential functions in coping with various stresses. In the present study, we found an apple (Malus domestica) homolog of Arabidopsis lipoxygenase3, named MdLOX3. MdLOX3 has a typical conserved lipoxygenase domain. MdLOX3 was expressed in all tissues of apple and was highly expressed in the root and flesh tissues by a qRT-PCR analysis. In addition, the promoter of MdLOX3 consists of multiple response elements. Various abiotic stresses and ABA treatment can induce the expression of MdLOX3. The overexpression of MdLOX3 in apple calli enhanced the ability to tolerate salt stress, and the heterotopic expression of MdLOX3 in Arabidopsis elevated salt stress tolerance via enhancing the ability of scavenging ROS. Furthermore, the overexpression of MdLOX3 in transgenic plants significantly reduced the sensitivity to ABA. Through the above, this work demonstrated that MdLOX3 played an active position in salt resistance and decreased the sensitivity to ABA, providing a theoretical reference for studying the role of MdLOX3 in abiotic stresses in apple.