Evidence that miR168a contributes to salinity tolerance of Brassica rapa L. via mediating melatonin biosynthesis

Abstract

Melatonin is a master regulator of diverse biological processes, including plant's abiotic stress responses and tolerance. Despite the extensive information on the role of melatonin in response to abiotic stress, how plants regulate endogenous melatonin content under stressful conditions remains largely unknown. In this study, we computationally mined Expressed Sequence Tag (EST) libraries of salinity‐exposed Chinese cabbage (Brassica rapa) to identify the most reliable differentially expressed miRNA and its target gene(s). In light of these analyses, we found that miR168a potentially targets a key melatonin biosynthesis gene, namely O‐METHYLTRANSFERASE 1 (OMT1). Accordingly, molecular and physiochemical evaluations were performed in a separate salinity experiment using contrasting B. rapa genotypes. Then, the association between B. rapa salinity tolerance and changes in measured molecular and physiochemical characteristics was determined. Results indicated that the expression profiles of miR168a and OMT1 significantly differed between B. rapa genotypes. Moreover, the expression profiles of miR168a and OMT1 significantly correlated with more melatonin content, robust antioxidant activities, and better ion homeostasis during salinity stress. Our results suggest that miR168a plausibly mediates melatonin biosynthesis, mainly through the OMT1 gene, under salinity conditions and thereby contributes to the salinity tolerance of B. rapa. To our knowledge, this is the first report on the role of miR168a and OMT1 in B. rapa salinity response.

Elucidating the modulatory effect of melatonin on enzyme activity and oxidative stress in wheat: a global meta‐analysis

“…Melatonin substantially enhanced the SOD, POD, CAT, and APX activities, likely due to its role as a signaling molecule in plant stress responses (Li et al 2019). It regulated the expression of genes associated with the antioxidant defense system, thereby upregulating enzymes' activity and mitigating oxidative stress caused by ROS production (Buttar et al 2020, Shamloo‐Dashtpagerdi et al 2023). Meta‐analysis showed that enzyme upregulation is particularly effective under temperature stress, suggesting that melatonin plays a crucial role in thermal stress tolerance in wheat (Buttar et al 2020, Iqbal et al 2021, Sehar et al 2023).…”

“…These variations may be attributed to melatonin's distinct modulation of stress‐specific pathways (Luo et al 2023, Zhang et al 2023). These studies highlight the need for a more comprehensive understanding of melatonin's role across various application method, concentrations, and experimental conditions to explore the stress‐specific regulatory mechanisms in wheat (Yang et al 2019, Shamloo‐Dashtpagerdi et al 2023).…”

Potential role of the regulatory miR1119-MYC2 module in wheat (Triticum aestivum L.) drought tolerance

“…Responses to drought include ROS bursts induced by osmotic stress, which cause membrane oxidation and damage ( Sachdev et al., 2021 ; Mansoor et al., 2022 ). Both enzymatic mechanisms (involving SOD, POD and CAT) and non-enzymatic mechanisms (involving proline and various antioxidants) detoxify ROS, maintain cellular ROS homeostasis (to varying genotype- and stress level-dependent degrees), and contribute to plants’ overall drought tolerance ( Laxa et al., 2019 ; Shamloo-Dashtpagerdi et al., 2022 ; Shamloo-Dashtpagerdi et al., 2022a ). ABA plays a major role in the induction of such adaptive responses in wheat to stresses, including drought ( Bano et al., 2012 ; Yu et al., 2020 ; Wang et al., 2021 ).…”

“…Water deficits also reportedly reduce expression of the miRNA-target modules miR159 - MYB , miR396 - GRF , miR535 - SPL , miR166b - HD-ZIP III and miR167 - ARF in cardamom ( Elettaria cardamomum Maton) ( Anjali et al., 2019 ). In addition, the miR168a - OMT1 module contributes to the salinity tolerance of Brassica rapa L., mainly through the regulation of melatonin biosynthesis ( Shamloo-Dashtpagerdi et al., 2022 ). There is also some evidence that the miR1118 - PIP1;5 module participates in wheat plants’ salinity tolerance through adjustment of their water status and ion homeostasis, and mitigation of membrane damage ( Shamloo-Dashtpagerdi et al., 2022c ).…”

Role of Melatonin in Directing Plant Physiology

“…CrCOMT from Carex iridescent overexpression alters MT production in Arabidopsis thaliana and causes an increase in salt stress [208]. In Brassica rapa, miR168a enhances the MT level through increased expression of the O-METHYLTRANSFERASE 1 (OMT1) gene, which is responsible for MT biosynthesis [209].…”