In recent years melatonin has emerged as a research highlight in plant studies. Melatonin has different functions in many aspects of plant growth and development. The most frequently mentioned ...functions of melatonin are related to abiotic stresses such as drought, radiation, extreme temperature, and chemical stresses. This review mainly focuses on the regulatory effects of melatonin when plants face harsh environmental conditions. Evidence indicates that environmental stress can increase the level of endogenous melatonin in plants. Overexpression of the melatonin biosynthetic genes elevates melatonin levels in transgenic plants. The transgenic plants show enhanced tolerance to abiotic stresses. Exogenously applied melatonin can also improve the ability of plants to tolerate abiotic stresses. The mechanisms by which melatonin alleviates abiotic stresses are discussed.
Melatonin is a ubiquitous molecule and exists across kingdoms including plant species. Studies on melatonin in plants have mainly focused on its physiological influence on growth and development, and ...on its biosynthesis. Much less attention has been drawn to its affect on genome-wide gene expression. To comprehensively investigate the role(s) of melatonin at the genomics level, we utilized mRNA-seq technology to analyze Arabidopsis plants subjected to a 16-hour 100 pM (low) and 1 mM (high) melatonin treatment. The expression profiles were analyzed to identify differentially expressed genes. 100 pM melatonin treatment significantly affected the expression of only 81 genes with 51 down-regulated and 30 up-regulated. However, 1 mM melatonin significantly altered 1308 genes with 566 up-regulated and 742 down-regulated. Not all genes altered by low melatonin were affected by high melatonin, indicating different roles of melatonin in regulation of plant growth and development under low and high concentrations. Furthermore, a large number of genes altered by melatonin were involved in plant stress defense. Transcript levels for many stress receptors, kinases, and stress-associated calcium signals were up-regulated. The majority of transcription factors identified were also involved in plant stress defense. Additionally, most identified genes in ABA, ET, SA and JA pathways were up-regulated, while genes pertaining to auxin responses and signaling, peroxidases, and those associated with cell wall synthesis and modifications were mostly down-regulated. Our results indicate critical roles of melatonin in plant defense against various environmental stresses, and provide a framework for functional analysis of genes in melatonin-mediated signaling pathways.
In this study, the effect of melatonin on the postharvest ripening and quality improvement of tomato fruit was carried out. The tomatoes were immersed in exogenous melatonin for 2 h, and then the ...related physiological indicators and the expression of genes during post-harvest life were evaluated. Compared with control check (CK) the 50 μM melatonin treatment significantly increased lycopene levels by 5.8-fold. Meanwhile, the key genes involved in fruit colour development, including phytoene synthase1 (PSY1) and carotenoid isomerase (CRTISO), showed a 2-fold increase in expression levels. The rate of water loss from tomato fruit also increased 8.3%, and the expression of aquaporin genes, such as SIPIP12Q, SIPIPQ, SIPIP21Q, and SIPIP22, was up-regulated 2- to 3-fold under 50 μM melatonin treatment. In addition, 50 μM melatonin treatment enhanced fruit softening, increased water-soluble pectin by 22.5%, and decreased protopectin by 19.5%. The expression of the cell wall modifying proteins polygalacturonase (PG), pectin esterase1 (PE1), β-galactosidase (TBG4), and expansin1 (Exp1) was up-regulated under 50 μM melatonin treatment. Melatonin increased ethylene production by 27.1%, accelerated the climacteric phase, and influenced the ethylene signalling pathway. Alteration of ethylene production correlated with altered 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS4) expression. The expression of ethylene signal transduction-related genes such as NR, SIETR4, SIEIL1, SIEIL3, and SIERF2, was enhanced by 50 μM melatonin. The effect of melatonin on ethylene biosynthesis, ethylene perception, and ethylene signalling may contribute to fruit ripening and quality improvement in tomato. This research may promote the application of melatonin on postharvest ripening and quality improvement of tomato fruit as well as other horticultural productions in the future.
Salt tolerance in plants is a complex trait involving multiple mechanisms. Understanding these mechanisms and their regulation will assist in developing novel strategies to engineer salt-tolerant ...crops. In the current study, we investigated salt-tolerant mechanisms in soybean (
Glycine max
) cultivar WF-7 in comparison to salt-sensitive Union. In vivo and in vitro salt assays demonstrated the salt tolerance of WF-7 at the seedling stage and during germination. After a 10-day 200 mM NaCl treatment, chlorophyll content in Union was reduced by 50 % compared to a 17 % reduction in WF-7. WF-7 was also less affected by abscisic acid (ABA) and NaCl during germination than Union. Upon ABA and NaCl treatment, the ABA-responsive genes
SCOF1
,
ASN1
,
bZIP44
, and
AAPK1
are differentially expressed in WF-7 and Union seedlings. These results suggest that salt tolerance in WF-7 is in part regulated through an ABA-dependent pathway. In addition, following a 4-day 200 mM NaCl treatment, WF-7 produced more H
2
O
2
than Union indicating the involvement of reactive oxygen species (ROS) in regulating salt tolerance in WF-7. Yet another mechanism WF-7 employs is withholding toxic chloride (Cl
−
) ions from aerial tissues. Following 200 mM NaCl treatment, Cl
−
accumulation was mostly localized to the roots of WF-7. In contrast, most of the Cl
−
in Union was transported into the stems and leaves. Taken together, our results demonstrated a role of ABA and ROS in regulating salt tolerance in WF-7, and the critical role of Cl
−
in NaCl-induced mortality in soybean.
Key message
Withholding toxic Cl
−
ions from leaves and, to a lesser extent, stems, confers salt tolerance to soybean WF-7. In addition, ABA and ROS may be involved in salt-stress signal transduction.
The soluble protein fraction of fully developed potato (Solanum tuberosum L.) tubers is dominated by patatin, a 40 kD storage glycoprotein, and protease inhibitors. Potato multicystatin (PMC) is a ...multidomain Cys-type protease inhibitor. PMC effectively inhibits degradation of patatin by tuber proteases in vitro. Herein we show that changes in PMC, patatin concentration, activities of various proteases, and their gene expression are temporally linked during tuber development, providing evidence that PMC has a role in regulating tuber protein content in vivo. PMC was barely detectable in non-tuberized stolons. PMC transcript levels increased progressively during tuberization, concomitant with a 40-fold increase in PMC concentration (protein basis) as tubers developed to 10 g fresh wt. Further increases in PMC were comparatively modest (3.7-fold) as tubers developed to full maturity (250 g). Protease activity declined precipitously as PMC levels increased during tuberization. Proteolytic activity was highest in non-tuberized stolons and fell substantially through the 10-g fresh wt stage. Cys-type proteases dominated the pre-tuberization and earliest stages of tuber development. Increases in patatin transcript levels during tuberization were accompanied by a notable lag in patatin accumulation. Patatin did not begin to accumulate substantially on a protein basis until tubers had reached the 10-g stage, wherein protease activity had been inhibited by approximately 60%. These results indicate that a threshold level of PMC (ca. 3 μg tuber⁻¹, 144 ng mg⁻¹ protein) is needed to favor patatin accumulation. Collectively, these results are consistent with a role for PMC in facilitating the accumulation of proteins in developing tubers by inhibiting Cys-type proteases.
The role of protease inhibitors in modulating changes in protein content of potato (Solanum tuberosum L.) tubers was investigated using a mother/daughter tuber model system. Changes in patatin, ...potato multicystatin (PMC), proteases, serine (Ser) protease inhibitors, and their gene expression were temporally coordinated over a 22-mo storage interval in genotypes with short (cv. Ranger Russet) and long (cv. Russet Burbank) dormancy. Daughter tubers were initiated on Ranger Russet tubers at approximately 15 mo. PMC (Cys protease inhibitor) declined linearly (approximately 4.2-fold) in Ranger Russet mother tubers from 4 to 15 mo and then maintained low levels through 22 mo. Conversely, protease activity was low and constant from 4 to 15 mo before increasing 7.4-fold through 22 mo. This increase coincided with the most rapid decline (54%) in patatin and the formation of daughter tubers. The proteases induced during aging of mother tubers were inhibited by PMC. Ser protease inhibitors were maintained in mother tubers throughout storage. In contrast, as daughter tubers developed, PMC and Ser protease inhibitors increased, protease activity declined to 17% of initial levels, and patatin increased threefold. These results implicate a role for protease inhibitors in regulating protein content during mobilization from mother tubers and deposition in daughter tubers.
: A comprehensive investigation was carried out to determine the changes that occurred in water‐stressed cucumber (Cucumis sativus L.) in response to melatonin treatment. We examined the potential ...roles of melatonin during seed germination and root generation and measured its effect on reactive oxygen species (ROS) levels, antioxidant enzyme activities, and photosynthesis. Melatonin alleviated polyethylene glycol induced inhibition of seed germination, with 100 μm melatonin‐treated seeds showing the greatest germination rate. Melatonin stimulated root generation and vitality and increased the root:shoot ratio; therefore, melatonin may have an effect on strengthening cucumber roots. Melatonin treatment significantly reduced chlorophyll degradation. Seedlings treated with 100 μm melatonin clearly showed a higher photosynthetic rate, thus reversing the effect of water stress. Furthermore, the ultrastructure of chloroplasts in water‐stressed cucumber leaves was maintained after melatonin treatment. The antioxidant levels and activities of the ROS scavenging enzymes, i.e., superoxide dismutase, peroxidase, and catalase, were also increased by melatonin. These results suggest that the adverse effects of water stress can be minimized by the application of melatonin.
Although previous studies have found that melatonin can promote seed germination, the mechanisms involved in perceiving and signaling melatonin remain poorly understood. In this study, it was found ...that melatonin was synthesized during cucumber seed germination with a peak in melatonin levels occurring 14 hr into germination. This is indicative of a correlation between melatonin synthesis and seed germination. Meanwhile, seeds pretreated with exogenous melatonin (1 μm) showed enhanced germination rates under 150 mm NaCl stress compared to water‐pretreated seeds under salinity stress. There are two apparent mechanisms by which melatonin alleviated salinity‐induced inhibition of seed germination. Exogenous melatonin decreased oxidative damage induced by NaCl stress by enhancing gene expression of antioxidants. Under NaCl stress, compared to untreated control, the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly increased by approximately 1.3–5.0‐fold, with a concomitant 1.4–2.0‐fold increase of CsCu‐ZnSOD, CsFe‐ZnSOD, CsCAT, and CsPOD in melatonin‐pretreated seeds. Melatonin also alleviated salinity stress by affecting abscisic acid (ABA) and gibberellin acid (GA) biosynthesis and catabolism during seed germination. Compared to NaCl treatment, melatonin significantly up‐regulated ABA catabolism genes (e.g., CsCYP707A1 and CsCYP707A2, 3.5 and 105‐fold higher than NaCl treatment at 16 hr, respectively) and down‐regulated ABA biosynthesis genes (e.g., CsNECD2, 0.29‐fold of CK2 at 16 hr), resulting in a rapid decrease of ABA content during the early stage of germination. At the same time, melatonin positively up‐regulated GA biosynthesis genes (e.g., GA20ox and GA3ox, 2.3 and 3.9‐fold higher than NaCl treatment at 0 and 12 hr, respectively), contributing to a significant increase of GA (especially GA4) content. In this study, we provide new evidence suggesting that melatonin alleviates the inhibitory effects of NaCl stress on germination mainly by regulating the biosynthesis and catabolism of ABA and GA4.
Cucumber is a model cucurbitaceous plant with a known genome sequence which is important for studying molecular mechanisms of root development. In this study, RNA sequencing was employed to explore ...the mechanism of melatonin‐induced lateral root formation in cucumber under salt stress. Three groups of seeds were examined, that is, seeds primed without melatonin (CK), seeds primed in a solution containing 10 or 500 μmol/L melatonin (M10 and M500, respectively). These seeds were then germinated in NaCl solution. The RNA‐seq analysis generated 16,866,670 sequence reads aligned with 17,920 genes, which provided abundant data for the analysis of lateral root formation. A total of 17,552, 17,450, and 17,393 genes were identified from roots of the three treatments (CK, M10 and M500, respectively). The expression of 121 genes was significantly up‐regulated, and 196 genes were significantly down‐regulated in M500 which showed an obvious increase on the number of lateral roots. These genes were significantly enriched in 57 KEGG pathways and 16 GO terms (M500 versus CK). Based on their expression pattern, peroxidase‐related genes were selected as the candidates to be involved in the melatonin response. Several transcription factor families might play important roles in lateral root formation processes. A number of genes related to cell wall formation, carbohydrate metabolic processes, oxidation/reduction processes, and catalytic activity also showed different expression patterns as a result of melatonin treatments. This RNA‐sequencing study will enable the scientific community to better define the molecular processes that affect lateral root formation in response to melatonin treatment.
The function of aquaporin (AQP) protein in transporting water is crucial for plants to survive in drought stress. With 47 homologues in tomato (Solanum lycopersicum) were reported, but the individual ...and integrated functions of aquaporins involved in drought response remains unclear. Here, three plasma membrane intrinsic protein genes, SlPIP2;1, SlPIP2;7 and SlPIP2;5, were identified as candidate aquaporins genes because of highly expressed in tomato roots. Assay on expression in Xenopus oocytes demonstrated that SlPIP2s protein displayed water channel activity and facilitated water transport into the cells. With real-time PCR and in situ hybridization analysis, SlPIP2s were considered to be involved in response to drought treatment. To test its function, transgenic Arabidopsis and tomato lines overexpressing SlPIP2;1, SlPIP2;7 or SlPIP2;5 were generated. Compared with wild type, the over-expression of SlPIP2;1, SlPIP2;7 or SlPIP2;5 transgenic Arabidopsis and tomato plants all showed significantly higher hydraulic conductivity levels and survival rates under both normal and drought conditions. Taken together, this study concludes that aquaporins (SlPIP2;1, SlPIP2;7 and SlPIP2;5) contribute substantially to root water uptake in tomato plants through improving plant water content and maintaining osmotic balance.
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