Transcriptome analysis of strawberry (Fragaria × ananassa) fruits under osmotic stresses and identification of genes related to ascorbic acid pathway

Differential response of phenylpropanoid pathway as linked to hormonal change in two Brassica napus cultivars contrasting drought tolerance

Oilseed rape (Brassica napus L.) is a significant agro-economic crop with a wide range of uses. Drought is the most frequent unfavourable environmental stressor restraining its growth and development worldwide. This study was conducted to characterize the drought-responsive phenylpropanoid pathway and its link to hormonal changes in two cultivars, drought-resistant "Saturnin" and drought-susceptible "Mosa." Drought susceptibility in cv. Mosa was confirmed by its lower water use efficiency and higher lipid peroxidation levels with reactive oxygen species (ROS) accumulation. In cv. Saturnin, higher salicylic acid (SA) levels and expression of dehydration-responsive element binding 2 (DREB2) and non-expressor of pathogenesis-related gene 1 (NPR1) led to an upregulation of production of anthocyanin pigment 1 (PAP1) and phenylpropanoid pathway-related gene (CHS, F5H and COMT1) expression, increasing hydroxycinnamic acid and flavonoid compound concentrations. However, in cv. Mosa, higher increases in the activity of lignifying enzymes (polyphenol oxidase, coniferyl alcohol peroxidase, syringaldazine peroxidase, guaiacol peroxidase) and expression of the lignin synthesis-related gene cinnamyl alcohol dehydrogenase 2 (CAD2) were found along with greater increases in abscisic acid (ABA) levels and upregulation of ABA-responsive element binding 2 (AREB2) and basic helix-loop-helix transcription factor MYC2. These results indicate that drought-induced SA-mediated activation of the hydroxycinnamic acid and flavonoid pathways contributes to drought resistance, whereas ABA-mediated lignification contributes to drought susceptibility.

Genome and Transcriptome Analyses of Genes Involved in Ascorbate Biosynthesis in Pepper Indicate Key Genes Related to Fruit Development, Stresses, and Phytohormone Exposures

Pepper (Capsicum annuum L.) is a vegetable consumed worldwide, primarily used for vitamin C uptake and condiment purposes. Ascorbate (Asc) is a multifunctional metabolite, acting as an antioxidant and enzymatic cofactor involved in multiple cellular processes. Nevertheless, there is no evidence about the contribution of biosynthesis pathways and regulatory mechanisms responsible for Asc reserves in pepper plants. Here, we present a genome- and transcriptome-wide investigation of genes responsible for Asc biosynthesis in pepper during fruit development, stresses, and phytohormone exposures. A total of 21 genes, scattered in ten of twelve pepper chromosomes were annotated. Gene expression analyses of nine transcriptomic experiments supported the primary role of the L-galactose pathway in the Asc-biosynthesizing process, given its constitutive, ubiquitous, and high expression profile observed in all studied conditions. However, genes from alternative pathways generally exhibited low expression or were unexpressed and appeared to play some secondary role under specific stress conditions and phytohormone treatments. Taken together, our findings provide a deeper spatio-temporal understanding of expression levels of genes involved in Asc biosynthesis, and they highlight GGP2, GME1 and 2, and GalLDH members from L-galactose pathway as promising candidates for future wet experimentation, addressing the attainment of increase in ascorbate content of peppers and other crops.

Citric acid assisted phytoextraction of nickle from soil helps to tolerate oxidative stress and expression profile of NRAMP genes in sunflower at different growth stages

Introduction

Soil polluted with Nickel (Ni) adversely affects sunflower growth resulting in reduced yield. Counterbalancing Ni toxicity requires complex molecular, biochemical, and physiological mechanisms at the cellular, tissue, and whole plant levels, which might improve crop productivity. One of the primary adaptations to tolerate Ni toxicity is the enhanced production of antioxidant enzymes and the elevated expression of Ni responsive genes.

Methods

In this study, biochemical parameters, production of ROS, antioxidants regulation, and expression of NRAMP metal transporter genes were studied under Ni stress in sunflower. There were four soil Ni treatments (0, 50, 100, and 200 mg kg-1 soil), while citric acid (CA, 5 mM kg-1 soil) was applied on the 28th and 58th days of plant growth. The samples for all analyses were obtained on the 30th and 60th day of plant growth, respectively.

Results and discussion

The results indicated that the concentrations of Ni in roots and shoots were increased with increasing concentrations of Ni at both time intervals. Proline contents, ascorbic acid, protein, and total phenolics were reduced under Ni-stress, but with the application of CA, improvement was witnessed in their contents. The levels of malondialdehyde and hydrogen peroxide were enhanced with the increasing concentration of Ni, and after applying CA, they were reduced. The contents of antioxidants, i.e., catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase, were increased at 50 ppm Ni concentration and decreased at higher concentrations of Ni. The application of CA significantly improved antioxidants at all concentrations of Ni. The enhanced expression of NRAMP1 (4, 51 and 81 folds) and NRAMP3 (1.05, 4 and 6 folds) was found at 50, 100 and 200ppm Ni-stress, respectively in 30 days old plants and the same pattern of expression was recorded in 60 days old plants. CA further enhanced the expression at both developmental stages.

Conclusion

In conclusion, CA enhances Ni phytoextraction efficiency as well as protect plant against oxidative stress caused by Ni in sunflower.

Exogenous brassinolide improves the antioxidant capacity of Pinellia ternata by enhancing the enzymatic and nonenzymatic defense systems under non-stress conditions

Brassinolide (BR) improves the antioxidant capacity of plants under various abiotic stresses. However, it is not clear about the effect of BR on the antioxidant capacity in plants under non-stress conditions. In the present study, the antioxidant defense response of Pinellia ternata was to be assessed by applying BR and propiconazole (Pcz) under non-stress conditions. BR treatment enhanced the flavonoid content, peroxidase, and ascorbate peroxidase (APX) activity by 12.31, 30.62, and 25.08% and led to an increase in 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity by 4.31% and a decrease in malondialdehyde content by 1.04%. Exogenous application of BR improved the expression levels of PAL, CHS, CHI, and DFR genes by 3. 18-, 3. 39-, 2. 21-, and 0.87-fold in flavonoid biosynthesis, PGI, PMI, and GME genes by 6. 60-, 1437. 79-, and 3.11-fold in ascorbic acid (ASA), biosynthesis, and γECs and GSHS genes by 6.08- and 2.61-fold in glutathione (GSH) biosynthesis pathway, and the expression of these genes were inhibited by Pcz treatment. In addition, BR treatment promoted the ASA-GSH cycle by enhancing the expression of APX, DHAR, and MDHAR genes, which were enhanced by 3. 33-, 157. 85-, and 154.91-fold, respectively. These results provided novel insights into the effect of BR on the antioxidant capacity in bulbil of P. ternata under non-stress conditions and useful knowledge of applying BR to enhance the antioxidant capacity of plants.

Stable Reference Gene Selection for qRT-PCR Normalization in Strawberry (Fragaria × ananassa) Leaves under Different Stress and Light-Quality Conditions

Selecting an appropriate reference gene is of crucial importance for improving the accuracy of qRT-PCR analyses. In this study, strawberry (Fragaria ananassa) seedlings were subjected to different environmental conditions including heat, cold, drought, salt, white-light, blue-light, and red-light treatments. The expression levels of seven candidate reference genes, including Fa18S, FaGAPDH, FaPIRUV, FaDBP, FaHISTH4, FaACTIN1, and FaACTIN2, in the strawberry leaves were measured by qRT-PCR. Then, four programs (geNorm, NormFinder, BestKeeper, and RefFinder) were employed as tools to evaluate the expression stability of the candidate reference genes. The results showed that the expression stability of the reference genes varied under different conditions. For the cold stress and white-light treatments, FaACTIN2 was evaluated to be the most stable reference gene. FaGAPDH should be used as the reference gene under salt-stress condition and red-light treatment. For the data normalization under drought-stress treatment, FaDBP is the recommended reference gene with the highest expression stability. FaHISTH4 was observed to be the best reference gene for data normalization under heat stress and blue-light treatment. This work provides information on selecting reference genes for accurate gene expression analyses of target genes in strawberry leaves under various abiotic stress and light-quality conditions.

Genome-wide identification, and characterization of the CDPK gene family reveal their involvement in abiotic stress response in Fragaria x ananassa

Calcium-dependent protein kinases (CDPKs) are encoded by a large gene family and play important roles against biotic and abiotic stresses and in plant growth and development. To date, little is known about the CDPK genes in strawberry (Fragaria x ananassa). In this study, analysis of Fragaria x ananassa CDPK gene family was performed, including gene structures, phylogeny, interactome and expression profiles. Nine new CDPK genes in Fragaria x ananassa were identified based on RNA-seq data. These identified strawberry FaCDPK genes were classified into four main groups, based on the phylogenetic analysis and structural features. FaCDPK genes were differentially expressed during fruit development and ripening, as well as in response to abiotic stress (salt and drought), and hormone (abscisic acid) treatment. In addition, the interaction network analysis pointed out proteins involved in the ABA-dependent response to plant stress via Ca2+ signaling, especially RBOHs. To our knowledge, this is the first report on CDPK families in Fragaria x ananassa, and it will provide valuable information for development of biofortified fruits and stress tolerant plants.

Abscisic acid and stress induced by salt: Effect on the phenylpropanoid, L-ascorbic acid and abscisic acid metabolism of strawberry fruits

Strawberry is one of the most popular fruits because of its sensorial and functional properties. However, strawberry crop is sensitive to salt stress conditions. Despite plants have plasticity, high salt concentrations induce molecular, biochemical, and physiological responses in plants. There is evidence that the abscisic acid (ABA) hormone acts as a signaling molecule under stress conditions; however, the molecular mechanisms involved in the synthesis and homeostasis of ABA and in the induction of phytochemical antioxidant compounds under stress conditions remain unclear. In this study, the effect of stress induced by NaCl (salt stress - SS), with or without the simultaneous application of ABA, on the ABA, phenylpropanoids and L-ascorbic acid (AsA) metabolisms were evaluated. The physiological aspects (Na, Cl and proline concentration, photosynthetic variables) were also studied. The results showed that salt stress increases the Na and Cl content in the leaves, affects photosynthetic variables and triggers the production of proline, pelargonidin-3-O-glucoside, total phenolic compounds and AsA content, alongside the upregulation of several genes from the phenylpropanoid and flavonoid pathways. These effects were accompanied by the induction of compounds and transcripts related to ABA biosynthesis, conjugation and catabolism. Otherwise, the exogenous application of ABA in salt stressed plants promotes a shift in gene expression and metabolism to mitigate the stress. Therefore, salt stress affects the metabolism of ABA, phenylpropanoids and AsA in strawberry increasing phytochemical composition which is strongly associated with an ABA-dependent mechanism.

Exogenous 5-aminolevulinic acid improves strawberry tolerance to osmotic stress and its possible mechanisms

Cultivated strawberry, one of the major fruit crops worldwide, is an evergreen plant with shallow root system, and thus sensitive to environmental changes, including drought stress. To investigate the effect of 5-aminolevulinic acid (ALA), a new environment-friendly plant growth regulator, on strawberry drought tolerance and its possible mechanisms, we treated strawberry (Fragaria × annanasa Duch. cv. 'Benihoppe') with 15% polyethylene glycol 6000 to simulate osmotic stress with or without 10 mg l^-1 ALA. We found that ALA significantly alleviated PEG-inhibited plant growth and improved water absorption and xylem sap flux, indicating ALA mitigates the adverse effect of osmotic stress on strawberry plants. Gas exchange and chlorophyll fluorescence analysis showed that ALA mitigated PEG-induced decreases of P_n , G_s , T_r , P_n /C_i , photosystem I and II reaction center activities, electron transport activity, and photosynthetic performance indexes. Equally important, ALA promoted PEG-increased antioxidant enzyme activities and repressed PEG-increased malondialdehyde and superoxide anion in both leaves and roots. Specially, ALA repressed H₂ O₂ increase in leaves, but stimulated it in roots. Furthermore, ALA repressed abscisic acid (ABA) biosynthesis and signaling gene expressions in leaves, but promoted those in roots. In addition, ALA blocked PEG-downregulated expressions of plasmalemma and tonoplast aquaporin genes PIP and TIP in both leaves and roots. Taken together, ALA effectively enhances strawberry drought tolerance and the mechanism is related to the improvement of water absorption and conductivity. The tissue-specific responses of ABA biosynthesis, ABA signaling, and H₂ O₂ accumulation to ALA in leaves and roots play key roles in ALA-improved strawberry tolerance to osmotic stress.

Untargeted metabolomics of strawberry (Fragaria x ananassa 'Camarosa') fruit from plants grown under osmotic stress conditions

BACKGROUND

Plants activate defense mechanisms to cope with adverse environmental conditions, leading to the accumulation and / or depletion of general and specialized metabolites. In this study, a multiplatform untargeted metabolomics strategy was employed to evaluate metabolic changes in strawberry fruit of cv. Camarosa grown under osmotic stress conditions. Liquid chromatography-mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) data from strawberries grown under two water-deficit conditions, irrigated at 95% crop evapotranspiration (ETc) and 85% ETc, and one excess salt condition with a 80 mmol L^-1 NaCl solution, were analyzed to determine treatment effects on fruit metabolism.

RESULTS

Multivariate principal component analysis, orthogonal projections to latent structures - discriminant analysis (OPLS-DA), and univariate statistical analyses were applied to the data set. While multivariate analyses showed group separation by treatment, T-tests and fold change revealed 12 metabolites differentially accumulated in strawberries from different treatments - among them phenolic compounds, glycerophospholipids, phytosterols, carbohydrates, and an aromatic amino acid.

CONCLUSION

Untargeted metabolomic analysis allowed for the annotation of compounds differentially accumulated in strawberry fruit from plants grown under osmotic stress and non-stressed plants. The metabolic disturbance in plants under stress involved metabolites associated with the inhibition of reactive oxygen species and cell-wall and membrane lipid biosynthesis, which might serve as osmotic stress biomarkers. © 2019 Society of Chemical Industry.