NADP-Malate Dehydrogenase of Sweet Sorghum Improves Salt Tolerance of <i>Arabidopsis thaliana</i>

Sweet sorghum is a C₄ crop that shows high salt tolerance and high yield. NADP-malate dehydrogenase (<i>NADP-ME</i>) is a crucial enzyme of the C₄ pathway. The regulatory mechanism of NADP-ME remains unclear. In this study, we isolated <i>SbNADP-ME</i> from sweet sorghum. The open reading frame of <i>SbNADP-ME</i> is 1911 bp and 637 amino acid residues. Quantitative real-time PCR analysis showed that <i>SbNADP-ME</i> transcription in sweet sorghum was enhanced by salt stress. The <i>SbNADP-ME</i> transcript level was highest under exposure to 150 mM NaCl. <i>Arabidopsis</i> overexpressing <i>SbNADP-ME</i> showed increased germination rate and root length under NaCl treatments. At the seedling stage, physiological photosynthesis parameters, chlorophyll content, PSII photochemical efficiency, and PSI oxidoreductive activity in the wild type decreased more severely than in the overexpression lines but less than in T-DNA insertion mutants under salt stress. Overexpression of <i>SbNADP-ME</i> in <i>Arabidopsis</i> may also increase osmotic adjustment and scavenging activity on DPPH and decrease membrane peroxidation. These results suggest that <i>SbNADP-ME</i> overexpression in <i>Arabidopsis</i> increases salt tolerance and alleviates PSII and PSI photoinhibition under salt stress by improving photosynthetic capacity