(1) Background: Alfalfa is an important legume forage throughout the world. Although alfalfa is considered moderately tolerant to salinity, its production and nitrogen-fixing activity are greatly limited by salt stress. (2) Methods: We examined the physiological changes and proteomic profiles of alfalfa with active nodules (NA) and without nodules (NN) under NaCl treatment. (3) Results: Our data suggested that NA roots showed upregulation of the pathways of abiotic and biotic stress responses (e.g., heat shock proteins and pathogenesis-related proteins), antioxidant enzyme synthesis, protein synthesis and degradation, cell wall degradation and modification, acid phosphatases, and porin transport when compared with NN plants under salt stress conditions. NA roots also upregulated the processes or proteins of lipid metabolism, heat shock proteins, protein degradation and folding, and cell cytoskeleton, downregulated the DNA and protein synthesis process, and vacuolar H⁺-ATPase proteins under salt stress. Besides, NA roots displayed a net H⁺ influx and low level of K⁺ efflux under salt stress, which may enhance the salt tolerance of NA plants. (4) Conclusions: The rhizobium symbiosis conferred the host plant salt tolerance by regulating a series of physiological processes to enhance stress response, improve antioxidant ability and energy use efficiency, and maintain ion homeostasis.

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-associated proteins are a class of transmembrane proteins involved in intracellular trafficking pathways. However, the functions of many SNARE domain-containing proteins remain unclear. We have previously identified a SNARE-associated gene in alfalfa (Medicago sativa) KILLING ME SLOWLY1 (MsKMS1), which is involved in various abiotic stresses. In this study, we investigated the function of MsKMS1 in the seed germination of transgenic tobacco (Nicotiana tabacum). Phylogenetic analysis showed that MsKMS1 was homologous to the SNARE-associated or MAPR component-related proteins of other plants. Germination assays revealed that MsKMS1 negatively regulated seed germination under normal, D-mannitol and abscisic acid-induced stress conditions, yet MsKMS1-overexpression could confer enhanced heat tolerance in transgenic tobacco. The suppressive effect on germination in MsKMS1-overexpression lines was associated with higher abscisic acid and salicylic acid contents in seeds. This was accompanied by the upregulation of abscisic acid biosynthetic genes (ZEP and NCED) and the downregulation of gibberellin biosynthetic genes (GA20ox2 and GA20ox3). Taken together, these results suggested that MsKMS1 negatively regulated seed germination by increasing abscisic acid and salicylic acid contents through the expression of genes related to abscisic acid and gibberellin biosynthesis. In addition, MsKMS1 could improve heat tolerance during the germination of transgenic tobacco seeds.

Drought severely limits maize yields. Water–saving irrigation methods like partial root–zone drying (PRD) can improve water use efficiency (WUE) but often result in variable yield responses among genotypes. We hypothesized that differences in root hydrotropism might contribute to some of this variability. Seven maize varieties were evaluated for hydrotropic response in a controlled moisture–gradient assay and then grown for five weeks under fixed PRD versus full irrigation in a greenhouse. The different maize varieties exhibited distinct hydrotropic behaviors: roots of V6 and V7 bent toward water much faster and more strongly, while V2 responded slowly with minimal curvature. Under PRD, genotypes also differed in root distribution and shoot performance. However, hydrotropism alone did not guarantee good shoot maintenance. One strongly hydrotropic genotype (V7) still suffered a large biomass reduction under PRD. Overall, genotypes that maintained better shoot water status, along with larger stem diameter and higher shoot water content, achieved the highest WUE under PRD. These results indicate that root hydrotropism varies widely in maize varieties. This variation was associated with shoot traits and WUE under PRD, suggesting that the benefit of hydrotropism for drought adaptation may depend on complementary shoot characteristics. Breeding for drought–resilient maize may therefore require combining strong root hydrotropism with the ability to maintain shoot function under water deficit.