Soil salinity is a severe abiotic stress that damages plant growth and development. As an antioxidant and free radical scavenger, melatonin is well known for helping plants survive abiotic conditions, including salinity stress. Here, we report that the salt-related gene MsSNAT1, encoding a rate-limiting melatonin biosynthesis enzyme, is located in the chloroplast and contributes to salinity stress tolerance in alfalfa. We found that the MsSNAT1 overexpressing alfalfa lines exhibited higher endogenous melatonin levels and increased tolerance to salt stress by promoting antioxidant systems and improving ion homeostasis. Furthermore, through a combination of transcriptome sequencing, dual-luciferase assays and transgenic analysis, we identified that the basic leucine zipper (bZIP) transcription factor, MsbZIP55, is associated with salt response and MsSNAT1 expression. EMSA analysis and ChIP-qPCR uncovered that MsbZIP55 can recognize and directly bind to the MsSNAT1 promoter in vitro and in vivo. MsbZIP55 acts as a negative regulator of MsSNAT1 expression, thereby reducing melatonin biosynthesis. Morphological analysis revealed that overexpressing MsbZIP55 conferred salt sensitivity to transgenic alfalfa through a higher Na+/K+ ratio and lower antioxidant activities, which could be alleviated by applying exogenous melatonin. Silencing of MsbZIP55 by RNA interference in alfalfa resulted in higher expression of MsSNAT1 and promoted salt tolerance by enhancing the antioxidant system enzyme activities and ion homeostasis. Our findings indicate that the MsbZIP55-MsSNAT1 module plays a crucial role in regulating melatonin biosynthesis in alfalfa while facilitating protection against salinity stress. These results shed light on the regulatory mechanism of melatonin biosynthesis related to the salinity stress response in alfalfa.

Soil salinity induces osmotic stress and ion toxicity in plants, detrimentally affecting their growth. Potato (So- lanum tuberosum) suffers yield reductions under salt stress. To understand salt-stress resilience mechanisms in potatoes, we studied three cultivars with contrasting salt sensitivity: Innovator, Desiree, and Mozart. Innovator emerged as the most resilient under salt stress, displaying minimal reductions in growth and plant tolerance index with no tuber yield loss, despite notable water loss. Conversely, Desiree experienced a significant tuber yield reduction but maintained better water retention. Mozart showed a low plant tolerance index and high water loss. Interestingly, ions measurement across different tissues revealed that, unlike chloride, sodium does not accumulate in tubers under salt stress in these cultivars, suggesting existence of an active sodium exclusion mechanism. A whole root transcriptomic analysis of these cultivars revealed a conserved salt stress response between potato and Arabidopsis. This response includes activation of various abiotic stress pathways and involves sequential activation of various transcription factor families. Root analyses showed that Innovator has lower suberin and lignin deposition, along with stronger K+ leakage in control conditions, resulting in a higher early stress response and increased ABA accumulation shortly after salt stress induction. This could explain Innovator has a more divergent transcriptomic response to salt stress compared to Desiree and Mozart. Nevertheless, Innovator displayed high suberin and lignin levels and ceased K+ leakage after salt stress, suggesting a high acclimation ability. Altogether, our results indicate that acclimation ability, rather than initial root protection against salt prevails in long-term salt-stress resilience of potato.

Soybean (Glycine max L.) is an important oilseed crop but is known to be sensitive to environmental challenges. Soil salinity is known to hamper soybean growth and yield significantly. Through this investigation, we tried to uncover the important insights into physiological, biochemical, and molecular responses and adaptive strategies of two Indian soybean cultivars - MAUS-47 (salt-tolerant) and Gujosoy-2 (salt-sensitive) to salinity stress. In a completely randomized block design experiment, plants of both cultivars were subjected to control (no salt treatment) and salt treatment (100 mM NaCl) at the trifoliate stage (10 plants of each cultivar per treatment with three biological replicates). Salinity stress generated reactive oxygen species (ROS), both free and non-free-radical forms, which seemingly triggered cell death as revealed by spectrophotometric histochemical analyses with significant varietal differences. Cultivars showed differential ROS-scavenging (enzymatic/non- antioxidative machinery) capabilities. The functioning of ion-accumulating channels differed between the two cultivars, with the sensitive cultivar exhibiting a higher intake of Na+ ions, leading to the replacement of essential K+, P+, and Mg2+ ions and thus ionic imbalances. This ion imbalance could be attributed to the yield damage, growth, and developmental delays in the sensitive cultivar under salt stress conditions. The expression pattern of 5 key genes representing salt-overly-sensitive (SOS) pathways, transcription factors, and antioxidant enzymes was revealed by qRT-PCR analysis. Differential expressions were observed for the genes corresponding to Na+/H+ antiporter (SOS1), transcription factors (WRKY and MYB), nitrate reductase-1, and superoxide dismutase (Cu-Zn). These findings thus shed light on the intricate mechanisms underlying salt stress responses in soybean and how tolerant and sensitive cultivars show differential strategies, offering valuable insights for developing salt-tolerant varieties and improved agricultural practices.