Melatonin Enhances Seed Germination and Seedling Growth of Medicago sativa Under Salinity via a Putative Melatonin Receptor MsPMTR1

Abstract

Alfalfa (Medicago sativa L.) is an important forage crop, and salt stress is a major limiting factor in its yield. Melatonin (MT) is a multi-regulatory molecule in plants. We showed that basal MT content was positively correlated with the salt tolerance degree of different alfalfa varieties. MT and its precursor 5-HT fully recovered seed germination while partially ameliorated seedling growth of salt-stressed alfalfa. The 5-HT showed some divergent effects from MT with regards to growth amelioration under salinity. Salt stress caused stunted plant growth in soil culture, while MT ameliorated it by elevating plant height, fresh weight, branching number, and chlorophyll content. Silencing of a putative MT receptor, MsPMTR1, which was shown to be membrane-localized, abolished the ameliorative effects of MT on salt-stressed alfalfa seedling growth, while overexpression of MsPMTR1 improved plant growth under salt stress. The RNA sequencing analysis showed that nine pathway genes were specifically induced by MT treatment compared with salt stress. These MT-responsive differentially expressed genes include basal metabolic pathway genes, such as “ribosome, elongation factor,” “sugar and lipid metabolism,” and “photosynthesis” and stress-related genes encoding “membrane integrity” related proteins, heat shock protein, peroxidase/oxidoreductase, and protease. Several abiotic stress response-related genes, such as DRE, ARF, HD-ZF, MYB, and REM were repressed by NaCl treatment while induced by MT treatment. In summary, we demonstrated the importance of MsPMTR1 in MT-mediated salt tolerance in alfalfa, and we also analyzed the regulatory mechanism of MT during alfalfa seed germination under salt stress.

Antioxidant Machinery and Glyoxalase System Regulation Confers Salt Stress Tolerance to Wheat (Triticum aestivum L.) Plants Treated with Melatonin and Salicylic Acid

“…In 1995, the MT was detected in the plant kingdom (Dubbels et al 1995) and now recognized as a ubiquitous biomolecule synthesized in all kingdoms, from prokaryotes to eukaryotes, from animals to plants (Arnao and Hernández-Ruiz 2014). Evidences indicate that MT is a plant master regulator that promote plant growth (Park et al 2021;Yu et al 2021) and crop yield (Zahedi et al 2020). Moreover, MT plays an important role in plant stress tolerance (Sun et al 2018;Khan et al 2020;Shafi et al 2021).…”

“…Exogenous application of MT induces tolerance to salt stress via enhancing photosynthetic efficiency, nitrogen metabolism, ion uptake, and antioxidant defense system (Ahmad et al 2021;Park et al 2021;Talaat 2021a,b;Talaat and Shawky 2022). There are also reports that exogenous MT improves crop salt tolerance by improving redox homeostasis, transcription factors, and plant hormones (Chen et al 2021;Zhang et al 2021b;Yu et al 2021). Treatment with exogenous MT has been shown to elevate the endogenous MT content (Li et al 2018a;Ni et al 2018).…”

The phytomelatonin receptor PMTR1 regulates seed development and germination by modulating abscisic acid homeostasis in Arabidopsis thaliana

“…20,21 Recently, putative MLT receptors also have been identified in Medicago sativa and maize, and they are proved to be involved in salinity, osmotic, and drought, respectively. 22,23 Beyond its role as a plant hormone, MLT also has been considered as an important regulator with diverse physiological functions in plant growth and development, due to its potential to modulate the expression of remarkable gene elements. 8 For example, MLT regulates the expression of the elements related to secondary metabolism, plant hormones biosynthesis, and catabolism.…”

“…PMTR1 was reported to function in governing the receptor‐dependent stomatal closure and osmotic stress tolerance 20,21 . Recently, putative MLT receptors also have been identified in Medicago sativa and maize, and they are proved to be involved in salinity, osmotic, and drought, respectively 22,23 …”

Overexpression of a Thioredoxin-Protein-Encoding Gene, MsTRX, from Medicago sativa Enhances Salt Tolerance to Transgenic Tobacco

“…Salinity, irrigation, and low temperature are the main limiting factors in alfalfa growth and production in northern China. Although alfalfa is considered a moderately salt-tolerant plant, planting alfalfa can reduce the salt content and improve the soil's physical and chemical properties [16]. Therefore, a comprehensive study and understanding of the salt-tolerant genes of alfalfa are helpful for the molecular breeding of alfalfa with salt tolerance.…”