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SnRK2 protein kinase family plays an important role in plant response to abiotic stress and has been identified in various plants. This study aimed to identify SnRK2 genes in tobacco and systematically analyze their expression under abscisic acid treatment and abiotic stress. We identified 22 NtSnRK2 members, which were divided into three groups and located on 13 chromosomes, mainly at both ends of the chromosomes; additionally, 11 duplicated NtSnRK2 gene pairs were observed. Phylogenetic analysis showed that these SnRK2 members were divided into three groups in tobacco. The motifs of NtSnRK2 proteins in the same group were highly similar. Subcellular localization indicated that NtSnRK2s in Group3 were present in the nucleus, cytomembrane, and cytoplasm. Gene expression pattern analysis revealed that NtSnRK2 genes played a role in the responses to several abiotic stresses (salt, drought, and low-temperature stress), indicating that they are widely involved in the adaptation of tobacco to adverse environmental conditions. [ABSTRACT FROM AUTHOR]

Melatonin is a well-known signaling molecule that mediates a range of physiological activities and various stress reactions in plants. We comprehensively tested the effect of melatonin on the development of root hairs and glandular trichomes and found that melatonin pretreatment of tobacco seeds significantly increased the length of root hairs. Furthermore, melatonin-treated tobacco exhibited significantly higher density of trichomes and larger glandular heads on long-stalk glandular trichomes than untreated plants, which resulted in enhanced secretion in glandular trichomes. Exogenous melatonin enhanced the aphid resistance of plants by facilitating the accumulation of cembranoids in the glandular trichomes and alleviated cadmium toxicity by increasing the Cd-exudation capacity of long glandular trichomes. Metabolic analysis indicated that the contents of 108 metabolites significantly changed upon melatonin treatment, with the contents of those that are directly/indirectly involved in melatonin metabolism changing the most. Further, KEGG pathway analysis suggested that the metabolic pathways of amino acids, reducing sugar, secondary metabolites, indole alkaloid biosynthesis, purine, pyrimidine, and ABC transporters were greatly influenced by exogenous melatonin application. Moreover, metabolisms of melatonin-related antioxidants and pyrimidine nucleoside antibiotics were enhanced after melatonin treatment. Melatonin improved tobacco resistance to high salinity, drought, and extreme temperature stresses, as indicated by improved photosynthetic and antioxidant capacities in treated vs. untreated plants. This study lays a foundation for the comprehensive application of melatonin to increase the stress tolerance of plants. [Display omitted] • Melatonin promoted the development of root hairs and glandular trichomes. • Exogenous melatonin enhanced aphid resistance of tobacco plants. • Melatonin facilitated the secretion of glandular trichomes. • Melatonin treatment alleviated cadmium toxicity in tobacco plants. • Exogenous melatonin enhanced the metabolism of some antioxidants. [ABSTRACT FROM AUTHOR]