Salinity is one of the most severe forms of abiotic stress and affects crop yields worldwide. Plants respond to salinity stress via a sophisticated mechanism at the physiological, transcriptional and metabolic levels. However, the molecular regulatory networks involved in salt and alkali tolerance have not yet been elucidated. We developed an RNA-seq technique to perform mRNA and small RNA (sRNA) sequencing of plants under salt (NaCl) and alkali (NaHCO₃) stress in tobacco. Overall, 8064 differentially expressed genes (DEGs) and 33 differentially expressed microRNAs (DE miRNAs) were identified in response to salt and alkali stress. A total of 1578 overlapping DEGs, which exhibit the same expression patterns and are involved in ion channel, aquaporin (AQP) and antioxidant activities, were identified. Furthermore, genes involved in several biological processes, such as “photosynthesis” and “starch and sucrose metabolism,” were specifically enriched under NaHCO₃ treatment. We also identified 15 and 22 miRNAs that were differentially expressed in response to NaCl and NaHCO₃, respectively. Analysis of inverse correlations between miRNAs and target mRNAs revealed 26 mRNA-miRNA interactions under NaCl treatment and 139 mRNA-miRNA interactions under NaHCO₃ treatment. This study provides new insights into the molecular mechanisms underlying the response of tobacco to salinity stress.

Melatonin (MEL) is a pleiotropic agent with crucial functions reported in a variety of stress responses and developmental processes. Although MEL involvement in plant defense against natural leaf senescence has been widely reported, the precise regulatory mechanisms by which it delays stress-induced senescence remain unclear. In this study, we found that foliar spraying of melatonin markedly ameliorated dehydration-induced leaf senescence in Nicotiana tabacum, accompanied by attenuated oxidative damage, expression of senescence-related genes, and reduced endogenous ABA production. Metabolite profiling indicated that melatonin-treated plants accumulated higher concentrations of sugars, sugar alcohol, and organic acids, but fewer concentrations of amino acids in the leaves, than untreated plants after exposure to dehydration. Gene expression analysis revealed that the delayed senescence of stressed plants achieved by melatonin treatment might be partially ascribed to the upregulated expression of genes involved in ROS scavenging, chlorophyll biosynthesis, photosynthesis, and carbon/nitrogen balances, and downregulated expression of senescence-associated genes. Furthermore, hormone responses showed an extensively modulated expression, complemented by carotenoid biosynthesis regulation to achieve growth acceleration in melatonin-treated plants upon exposure to dehydration stress. These findings may provide more comprehensive insights into the role of melatonin in alleviating leaf senescence and enhancing dehydration resistance.

Maca (Lepidium meyenii Walp.) is a traditional Andean crop with great potential for various sanitarian and medical functions, which is attracting increased research attention. The majority of previous Maca studies were focused on biochemistry and pharmacodynamics, while the genetic basis of its unique characteristics lagged due to a lack of genome information. The authors perform gas chromatography-mass spectrometry (GC/MS) analysis in the hypocotyls of three Maca ecotypes and identify 79 compounds. Among them, 62 compounds have distinct profiles among Maca ecotypes. To reveal the underlying regulatory mechanism of the chemical composition differences, de novo transcriptome sequencing is performed and the transcription profiles of three Maca ecotypes are comparatively analyzed. Functional analysis indicates several key pathways, including “starch and sucrose metabolism,” “phenylpropanoid biosynthesis,” “phenylalanine metabolism” and “plant-pathogen interaction,” are involved in regulating the chemical compositions of Maca. Combining metabolomics and transcriptomics analysis indicates transcription factors such as MYB and WRKY and mediators such as protein kinase and bifunctional inhibitors might be critical regulators of chemical composition in Maca. The transcriptome reference genome and differentially expressed genes (DEGs) obtained in this study might serve as an initial step to illustrate the genetic differences in nutrient component, secondary metabolites content, medicinal function and stress resistance in Maca.