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Background: Salt stress seriously impacts the plantation and productivity of global alfalfa (Medicago sativa). Previously, we genetically defined the M. sativa DROUGHT-INDUCED UNKNOWN PROTEIN 1 (MsDIUP1) as a drought tolerance gene of alfalfa. However, whether it is associated with salt tolerance needs to be explored. Results: In this study, we re-classified MsDIUP1 as a putative novel late embryogenesis abundant protein, and found its promoter activity was strongly induced by salt and ABA treatment. Heterologous overexpression of MsDIUP1 in Arabidopsis led to enhanced salt tolerance and ABA insensitivity, with a higher fresh weight, lateral root number, primary root length, and survival rate compared to the wild-type (WT) plants. Similarly, homologous overexpression of MsDIUP1 also enhanced the salt tolerance of alfalfa over-expression (OE) plants, accompanied by reduced oxidative damage, higher K+/Na+ ratio, increased osmoprotectant accumulation, and improved photosynthetic capacity relative to the WT plants. In reverse, disruption of MsDIUP1 expression caused a salt-hypersensitive phenotype of alfalfa RNA interference (RNAi) plants, with higher oxidative damage, less osmoprotectant accumulation, and lower photosynthetic pigment content than that of the WT. These physiological discoveries were in accordance with differential transcript profiles of the relevant genes associated with stress signaling, antioxidant defense, and osmotic adjustment in the salt-treated alfalfa WT, OE, and RNAi lines. Furthermore, we found that alfalfa OE plants showed no apparent alteration in their forage quality compared with the WT plants. Conclusions: Overall, these results reveal that MsDIUP1 improves plant salt tolerance via regulating stress signaling, antioxidant defense, ion homeostasis, osmotic adjustment, and photosynthesis. [ABSTRACT FROM AUTHOR]

Excess copper (Cu) in soil due to industrial and agricultural practices can result in reduced plant growth. Excess Cu resulted in severely retarded root growth with severe discoloration of Alfalfa (Medicago sativa) and Medicago truncatula. Growth in the presence of hydrogen peroxide resulted in similar symptoms that could be partially recovered by the addition of the reductant ascorbic acid revealing damage was likely due to oxidative stress. The addition of proanthocyanidins (PAs) in the presence of Cu prevented much of the damage, including plant growth and restoration of lignin synthesis which was inhibited in the presence of excess Cu. Transcriptome analyses of the impact of excess Cu and the amelioration after PAs treatment revealed that changes were enriched in functions associated with the cell wall and extracellular processes, indicating that inhibition of cell wall synthesis was likely the reason for retarded growth. Excess Cu appeared to induce a strong defense response, along with alterations in the expression of a number of genes encoding transcription factors, notably related to ethylene signaling. The addition of PAs greatly reduced this response, and also induced novel genes that likely help ameliorate the effects of excess Cu. These included induction of genes involved in the last step of ascorbic acid biosynthesis and of enzymes involved in cell wall synthesis. Combined, these results show that excess Cu causes severe oxidative stress damage and inhibition of cell wall synthesis, which can be relieved by the addition of PAs. [ABSTRACT FROM AUTHOR]