Cucumber (Cucumis sativus L.) Nitric Oxide Synthase Associated Gene1 (CsNOA1) Plays a Role in Chilling Stress

Combination of Sodium Nitroprusside and Controlled Atmosphere Maintains Postharvest Quality of Chestnuts through Enhancement of Antioxidant Capacity

The purpose of this study was to clarify the effect of CA (controlled atmosphere, 2-3% O2 + 3% CO2) and NO (nitric oxide, generated by 0.4 nM sodium nitroprusside), alone or combined (CA + NO), on the physio-chemical properties, enzyme activities and antioxidant capacities of chestnuts during storage at 0 °C for 180 d. Compared with control (CT), CA and CA+NO both improved the storage quality of the samples, but only CA resulted in more ethanol production. Moreover, these improvements were further enhanced and ethanol synthesis was inhibited by the addition of NO. A spectrometer was used to assess the production of phenolic content (TPC) and activities of phenylalanine ammonia-lyase (PAL), superoxide dismutas (SOD), peroxidase (POD), catalase (CAT) and polyphenol oxidase (PPO) as influenced by CA or CA+NO treatments. Higher TPC, PAL, SOD, POD, CAT, and lower PPO were observed in CA alone, and more so in the combination with NO group. The increased antioxidant production and enhanced antioxidant activities contributed to scavenging reactive oxygen species (ROS) and reducing malondialdehyde (MDA). This study unveiled the correlations and differences between the effects of CA and CA+NO on storage quality, providing valuable insights into postharvest preservation and suggesting that the combination (CA+NO) was more beneficial for quality maintenance in chestnuts.

Multiple Ways of Nitric Oxide Production in Plants and Its Functional Activity under Abiotic Stress Conditions

Nitric oxide (NO) is an endogenous signaling molecule that plays an important role in plant ontogenesis and responses to different stresses. The most widespread abiotic stress factors limiting significantly plant growth and crop yield are drought, salinity, hypo-, hyperthermia, and an excess of heavy metal (HM) ions. Data on the accumulation of endogenous NO under stress factors and on the alleviation of their negative effects under exogenous NO treatments indicate the perspectives of its practical application to improve stress resistance and plant productivity. This requires fundamental knowledge of the NO metabolism and the mechanisms of its biological action in plants. NO generation occurs in plants by two main alternative mechanisms: oxidative or reductive, in spontaneous or enzymatic reactions. NO participates in plant development by controlling the processes of seed germination, vegetative growth, morphogenesis, flower transition, fruit ripening, and senescence. Under stressful conditions, NO contributes to antioxidant protection, osmotic adjustment, normalization of water balance, regulation of cellular ion homeostasis, maintenance of photosynthetic reactions, and growth processes of plants. NO can exert regulative action by inducing posttranslational modifications (PTMs) of proteins changing the activity of different enzymes or transcriptional factors, modulating the expression of huge amounts of genes, including those related to stress tolerance. This review summarizes the current data concerning molecular mechanisms of NO production and its activity in plants during regulation of their life cycle and adaptation to drought, salinity, temperature stress, and HM ions.

CsMYC2 is involved in the regulation of phenylpropanoid biosynthesis induced by trypsin in cucumber (Cucumis sativus) during storage

Trypsin has a new activity of scavenging superoxide anion and generating hydrogen peroxide. Trypsin can significantly improve the storage quality of C. sativus. To illustrate the mechanism of trypsin-induced resistance in fruits and vegetables, an integrated analysis of widely targeted metabolomics and transcriptomics was carried out. Transcriptomic results showed that 1068 genes highly related to phenylpropanoid biosynthesis gathered in the brown module were obtained by WGCNA. In KEGG analysis, differentially expressed genes (DEGs) were also highly enriched in EIP (Environmental Information Processing) pathways "Plant hormone signal transduction (map04075)" and "MAPK signaling pathway-plant (map04016)". Next, 87 genes were identified as the leading edge by GSEA analysis. So far, CsMYC2 was highlighted as a key transcription factor that regulates phenylpropanoid biosynthesis identified by GSEA and WGCNA. Furthermore, the major route of biosynthesis of phenylpropanoid compounds including coumarins, lignins, chlorogenic acid, flavonoids, and derivatives regulated by trypsin was also illustrated by both transcriptomic and metabolomic data. Results of O2PLS showed that CsMYC2 was positively correlated with Rosmarinic acid-3-O-glucoside, Epigallocatechin, Quercetin-3-O-sophoroside (Baimaside), and so on. Correlation between CsMYC2, phenylpropanoid related genes, and metabolites in C. sativus was illustrated by co-expression networks. Roles of CsMYC2 were further checked in C. sativus by VIGS. The results of this study might give new insight into the exploration of the postharvest resistance mechanism of C. sativus induced by trypsin and provide useful information for the subsequent mining of resistance genes in C. sativus.

Genome-wide analysis of MYB transcription factors of Vaccinium corymbosum and their positive responses to drought stress

Background

Blueberry (Vaccinium corymbosum L.) is an important species with a high content of flavonoids in fruits. As a perennial shrub, blueberry is characterized by shallow-rooted property and susceptible to drought stress. MYB transcription factor was reported to be widely involved in plant response to abiotic stresses, however, the role of MYB family in blueberry responding to drought stress remains elusive.

Results

In this study, we conducted a comprehensive analysis of VcMYBs in blueberry based on the genome data under drought stress, including phylogenetic relationship, identification of differentially expressed genes (DEGs), expression profiling, conserved motifs, expression correlation and protein-protein interaction prediction, etc. The results showed that 229 non-redundant MYB sequences were identified in the blueberry genome, and divided into 23 subgroups. A total of 102 MYB DEGs with a significant response to drought stress were identified, of which 72 in leaves and 69 in roots, and 8 differential expression genes with a > 20-fold change in the level of expression. 17 DEGs had a higher expression correlation with other MYB members. The interaction partners of the key VcMYB proteins were predicted by STRING analysis and in combination with physiological and morphological observation. 10 key VcMYB genes such as VcMYB8, VcMYB102 and VcMYB228 were predicted to be probably involved in reactive oxygen species (ROS) pathway, and 7 key VcMYB genes (VcMYB41, VcMYB88 and VcMYB100, etc..) probably participated in leaf regulation under drought treatment.

Conclusions

Our studies provide a new understanding of the regulation mechanism of VcMYB family in blueberry response to drought stress, and lay fundamental support for future studies on blueberry grown in regions with limited water supply for this crop.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07850-5.

Melatonin Inhibits Ethylene Synthesis via Nitric Oxide Regulation To Delay Postharvest Senescence in Pears

Understanding ripening and senescence processes in postharvest stored fruit is key to the identification and implementation of effective treatment methods. Here, we explored the effects of exogenous applications of melatonin (MT) and nitric oxide (NO) on ripening and softening processes in three cultivars of European pear ( Pyrus communis L.). The results showed that MT and NO played important roles in the two processes: they decreased the rate of upregulation of PcCel and PcPG, inhibited expression of ethylene synthetase genes ( PcACS and PcACO), and reduced rates of respiration and ethylene production. MT increased activity of NO synthase through upregulation of expression of PcNOS that subsequently led to an increase in NO content. However, when NO synthesis was inhibited, the delaying effect of MT on fruit senescence was almost eliminated. These findings indicate that MT acted on the upstream process of NO synthesis that then delayed senescence in pear fruit.

OsNOA1 functions in a threshold-dependent manner to regulate chloroplast proteins in rice at lower temperatures

BACKGROUND

Although decreased protein expressions have been observed in NOA1 (Nitric Oxide Associated protein 1) deficient plants, the molecular mechanisms of how NOA1 regulates protein metabolism remain poorly understood. In this study, we have used a global comparative proteomic approach for both OsNOA1 suppression and overexpression transgenic lines under two different temperatures, in combination with physiological and biochemical analyses to explore the regulatory mechanisms of OsNOA1 in rice.

RESULTS

In OsNOA1-silenced or highly overexpressed rice, considerably different expression patterns of both chlorophyll and Rubisco as well as distinct phenotypes were observed between the growth temperatures at 22 °C and 30 °C. These observations led us to hypothesize there appears a narrow abundance threshold for OsNOA1 to function properly at lower temperatures, while higher temperatures seem to partially compensate for the changes of OsNOA1 abundance. Quantitative proteomic analyses revealed higher temperatures could restore 90% of the suppressed proteins to normal levels, whereas almost all of the remaining suppressed proteins were chloroplast ribosomal proteins. Additionally, our data showed 90% of the suppressed proteins in both types of transgenic plants at lower temperatures were located in the chloroplast, suggesting a primary effect of OsNOA1 on chloroplast proteins. Transcript analyses, along with in vitro pull-down experiments further demonstrated OsNOA1 is associated with the function of chloroplast ribosomes.

CONCLUSIONS

Our results suggest OsNOA1 functions in a threshold-dependent manner for regulation of chloroplast proteins at lower temperatures, which may be mediated by interactions between OsNOA1 and chloroplast ribosomes.

Exogenous Hydrogen Peroxide Contributes to Heme Oxygenase-1 Delaying Programmed Cell Death in Isolated Aleurone Layers of Rice Subjected to Drought Stress in a cGMP-Dependent Manner

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that plays a dual role in plant cells. Here, we discovered that drought (20% polyethylene glycol-6000, PEG)-triggered decreases of HO-1 transcript expression and HO activity. However, exogenous H2O2 contributed toward the increase in HO-1 gene expression and activity of the enzyme under drought stress. Meanwhile, the HO-1 inducer hematin could mimic the effects of the H2O2 scavengers ascorbic acid (AsA) and dimethylthiourea (DMTU) and the H2O2 synthesis inhibitor diphenyleneiodonium (DPI) for scavenging or diminishing drought-induced endogenous H2O2. Conversely, the zinc protoporphyrin IX (ZnPPIX), an HO-1-specific inhibitor, reversed the effects of hematin. We further analyzed the endogenous H2O2 levels and HO-1 transcript expression levels of aleurone layers treated with AsA, DMTU, and DPI in the presence of exogenous H2O2 under drought stress, respectively. The results showed that in aleurone layers subjected to drought stress, when the endogenous H2O2 level was inhibited, the effect of exogenous H2O2 on the induction of HO-1 was enhanced. Furthermore, exogenous H2O2-activated HO-1 effectively enhanced amylase activity. Application of 8-bromoguanosine 3',5'-cyclic guanosine monophosphate (8-Br-cGMP) (the membrane permeable cGMP analog) promoted the effect of exogenous H2O2-delayed PCD of aleurone layers in response to drought stress. More importantly, HO-1 delayed the programmed cell death (PCD) of aleurone layers by cooperating with nitric oxide (NO), and the delayed effect of NO on PCD was achieved via mediation by cGMP under drought stress. In short, in rice aleurone layers, exogenous H2O2 (as a signaling molecule) triggered HO-1 and delayed PCD via cGMP which possibly induced amylase activity under drought stress. In contrast, as a toxic by-product of cellular metabolism, the drought-generated H2O2 promoted cell death.

Involvement of NR and PM-NR in NO biosynthesis in cucumber plants subjected to salt stress

Nitrate reductase (NR) mainly reduces nitrate to nitrite. However, in certain conditions it can reduce nitrite to NO. In plants, a plasma membrane-associated form of NR (PM-NR) is present. It produces NO₂^- for nitrite NO/reductase (Ni-NOR), which can release NO into the apoplastic space. The effect of 50 mM NaCl on NO formation and the involvement of NR in NO biosynthesis were studied in cucumber seedling roots under salt stress. In salt-stressed roots, the amount of NO was higher than in control. The application of tungstate abolished the increase of NO level in stressed roots, indicating that NR was responsible for NO biosynthesis under the test conditions. The involvement of other molybdoenzymes was excluded using specific inhibitors. Furthermore, higher cNR and PM-NR activities were observed in NaCl-treated roots. The increase in NR activity was due to the stimulation of CsNR genes expression and posttranslational modifications, such as enzyme dephosphorylation. This was confirmed by Western blot analysis. Moreover, the increase of nitrite tissue level in short-term stressed roots and the nitrite/nitrate ratio, with a simultaneous decrease of nitrite reductase (NiR) activity, in both short- and long-term stressed roots, could promote the production of NO by NR in roots under salt stress.