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Co-expression of Arabidopsis AtAVP1
 and AtNHX1
 to Improve Salt Tolerance in Soybean

Salinity is one of the major abiotic stresses affecting plant productivity. Soybean [Glycine max (L.) Merr.] is moderately sensitive to saltaffected soils. In this study, Arabidopsis vacuolar H+-pyrophosphatase gene (AtAVP1) and a vacuolar Na+/H+ antiporter gene (AtNHX1) were co-expressed to determine if the compartmentation of Na+ in vacuole is feasible to improve salt tolerance in soybean. The transgenic plants co-expressing AtAVP1 and AtNHX1 enhanced salt tolerance compared with those expressing individual AtAVP1 or AtNHX1, which were more tolerant than the nontransgenic control plants. These transgenic plants had higher chlorophyll content, cell membrane stability, and photosynthetic rate under both 100 and 200 mM NaCl treatments, whereas biomass was different only in the treatment of 100 mM NaCl. Analyses of Na+ content in roots and leaves showed that the tolerance of the transgenic plants was likely the contribution of both higher Na+ sequestration in the vacuoles and cellular protection mechanisms. Under longer exposure to mild NaCl stress condition (electrical conductivity ? 7.5 dS m−1); however, the transgenic plants did not have higher biomass and grain yield than the nontransgenic soybean. The data suggest that the expression of AtAVP1 and AtNHX1 benefits the transgenic soybean in short-term salinity. For longer salt exposure, they might be more beneficial if coupled with lower Na+ accumulation regulators. To this end, coupling their expression with genes controlling Na+ uptake and long-distance transport such as SOS1, a plasma membrane Na+/H+ antiporter, might be more efficient in improving salt tolerance in soybean. N.T. Nguyen, T.T. Nguyen, L.-A.T. Nguyen, M.-C.D. Nguyen, K.T. Nguyen, and T.N. Quach, Dep. of Plant Physiology, Biochemistry and Product Quality, Field Crops Research Institute, Hanoi, Vietnam; H.T. Vu, Vietnam National Univ. of Agriculture, Hanoi, Vietnam; K.L. Hoang and T.N. Quach, Center for Plant Science Innovation, Univ. of Nebraska Lincoln, NE 68588. Received 22 Oct. 2018. Accepted 24 Jan. 2019. *Corresponding author (Tquach2@unl.edu). Assigned to Associate Editor Rongda Qu. Abbreviations: EC, electrical conductivity; PCR, polymerase chain reaction; WT, wild type. Published in Crop Sci. 59:1133–1143 (2019). doi: 10.2135/cropsci2018.10.0640 © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Published May 16, 2019