| Summary: | The NADP-malic enzyme (NADP-ME) catalyzes the reversible decarboxylation of L-malate to produce pyruvate, CO<sub>2</sub>, and NADPH in the presence of a bivalent cation. In addition, this enzyme plays crucial roles in plant developmental and environment responses, especially for the plastidic isoform. However, this isoform is less studied in C<sub>3</sub>–C<sub>4</sub> intermediate species under drought and salt stresses than in C<sub>3</sub> and C<sub>4</sub> species. In the present study, we characterized <i>SaNADP-ME4</i> from the intermediate woody desert species <i>Salsola laricifolia</i>. <i>SaNADP-ME4</i> encoded a protein of 646 amino acids, which was found to be located in the chloroplasts based on confocal imaging. Quantitative real-time PCR analysis showed that <i>SaNADP-ME4</i> was highly expressed in leaves, followed by stems and roots, and <i>SaNADP-ME4</i> expression was improved and reached its maximum under the 200 mm mannitol and 100 mm NaCl treatments, respectively. <i>Arabidopsis</i> overexpressing <i>SaNADP-ME4</i> showed increased root length and fresh weight under mannitol and salt stress conditions at the seedling stage. In the adult stage, <i>SaNADP-ME4</i> could alleviate the decreased in chlorophyll contents and PSII photochemical efficiency, as well as improve the expression of superoxide dismutase, peroxidase, and pyrroline-5-carboxylate synthase genes to enhance reactive oxygen species scavenging capability and proline levels. Our results suggest that <i>SaNADP-ME4</i> overexpression in <i>Arabidopsis</i> increases drought and salt stress resistance.
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