Overexpression of the MhTGA2 gene from crab apple (Malus hupehensis) confers increased tolerance to salt stress in transgenic apple (Malus domestica)

Abstract

SUMMARYLeaves of Nagafu No. 6 were transformed by the Agrobacterium tumefaciens-mediated method, and 158 hyg-resistant buds were obtained. Using fresh leaf tissue, seven positive lines were obtained by polymerase chain reaction (PCR) with total DNA, and four by reverse transcriptase–polymerase chain reaction (RT–PCR) with total RNA. The results showed that the MhTGA2 gene was successfully transformed into Nagafu No. 6 plants and expressed. At 4 months after transplanting, photosynthetic parameters of young leaves were determined using transgenic and control plants prior to the determination of leaf surface characteristics (epidermal structure and stomatal distribution) by scanning electronic microscopy. The results showed that the net photosynthesis rate, the instantaneous carboxylation rate and stomatal conductance of transgenic plants were higher than the control, whereas the internal carbon dioxide (CO2) concentrations of the transgenic plants were lower. Under non-saline conditions, the stomata of the transgenic plants were better distributed than in the control. Under saline conditions, the epidermal structure of the control leaves was severely hypohydrated and the quantity of stomata was significantly decreased. Conversely, the epidermal structure of transgenic leaves was not significantly altered, indicating salt-stress tolerance. The overall results suggested that MhTGA2 may play a crucial role in the response to salt stress in Nagafu No. 6.