Abscisic Acid Accumulation Research Articles

OsWRKY53 Promotes Abscisic Acid Accumulation to Accelerate Leaf Senescence and Inhibit Seed Germination by Downregulating Abscisic Acid Catabolic Genes in Rice.

Abscisic acid (ABA) largely promotes leaf senescence and inhibits seed germination in plants. Endogenous ABA content is finely tuned by many transcription factors. In this study, we showed that OsWRKY53 is a positive regulator of leaf senescence and a negative regulator of seed germination in rice. OsWRKY53 expression was induced in leaves under aging, dark, and ABA treatment. The OsWRKY53-overexpressing (OsWRKY53-oe) plants showed early yellowing leaves, while the OsWRKY53 (oswrky53) knockout mutants maintained green leaves than the wild type under natural, dark-induced, and ABA-induced senescence conditions. Transcriptional analysis revealed that ABA catabolic genes, namely, OsABA8ox1 and OsABA8ox2, two key genes participating in ABA catabolism harboring ABA 8′-hydroxylase activity, were markedly downregulated in OsWRKY53-oe leaves. Chromatin immunoprecipitation and protoplast transient assays revealed that OsWRKY53 directly bound to the promoters of OsABA8ox1 and OsABA8ox2 to repress their transcription, resulting in elevated endogenous ABA contents that promoted premature leaf senescence in the OsWRKY53-oe plants. It indicates that OsWRKY53 is a positive regulator through regulating ABA accumulation to promote leaf senescence. In addition, accumulated ABA simultaneously inhibited seed germination and post-germination growth in OsWRKY53-oe plants. Taken together, OsWRKY53 suppresses the transcript of ABA catabolic genes to promote ABA accumulation to modulate ABA-induced leaf senescence and ABA-mediated inhibition of seed germination.

Fluoride tolerance in rice is negatively regulated by the 'stress-phytohormone' abscisic acid (ABA), but promoted by ABA-antagonist growth regulators, melatonin, and gibberellic acid.

The present manuscript aimed at investigating whether abscisic acid (ABA) promotes fluoride tolerance, similar to inciting salt adaptation in rice. Seeds of three salt-tolerant rice genotypes were maintained at 32°C under 16/8h light/dark photoperiodic cycle with 700μmol photons m-2s-1 intensity and 50% relative humidity in a plant growth chamber for 20days. Suppressed ABA biosynthesis, and downregulated expression of ABA-inducible genes like Rab16A, Osem, and TRAB1 triggered NaCl-induced growth inhibition and physiological injuries like chlorophyll degradation, electrolyte leakage, formation of H2O2, malondialdehyde, and methylglyoxal in Matla. Reduced ABA accumulation increased the levels of melatonin and gibberellic acid in NaF (50mgL-1)-stressed Nonabokra and Matla, which altogether promoted fluoride tolerance. Higher ABA content in NaF-stressed Jarava stimulated fluoride uptake via chloride channels, thus exhibiting severe fluoride susceptibility, in spite of higher production of ABA-associated osmolytes like proline, glycine-betaine and polyamines via the concerted action of genes like PDH, ADC, ODC, SAMDC, SPDS, SPMS, DAO, and PAO. Increased accumulation of compatible solutes in presence of high endogenous ABA promoted salt tolerance in Jarava; the same was insufficient to ameliorate fluoride-induced injuries in this cultivar. Treatment with ABA biosynthetic inhibitor, Na2WO4 promoted fluoride tolerance in Jarava, whereas further supplementation with exogenous ABA resulted in reversion back to fluoride-susceptible phenotype. Our work clearly established that ABA cannot always be considered as a 'universal' stress hormone as known in literature, since it acts as a negative regulator of fluoride tolerance which is more tightly regulated in rice via melatonin- and gibberellic acid-dependent pathways in ABA-independent manner.

Transcriptome Analysis Reveals Multiple Genes and Complex Hormonal-Mediated Interactions with PEG during Adventitious Root Formation in Apple.

Adventitious root (AR) formation is a bottleneck for the mass propagation of apple rootstocks, and water stress severely restricts it. Different hormones and sugar signaling pathways in apple clones determine AR formation under water stress, but these are not entirely understood. To identify them, GL-3 stem cuttings were cultured on polyethylene glycol (PEG) treatment. The AR formation was dramatically decreased compared with the PEG-free control (CK) cuttings by increasing the endogenous contents of abscisic acid (ABA), zeatin riboside (ZR), and methyl jasmonate (JA-me) and reducing the indole-3-acetic acid (IAA) and gibberellic acid 3 (GA3) contents. We performed a transcriptomic analysis to identify the responses behind the phenotype. A total of 3204 differentially expressed genes (DEGs) were identified between CK and PEG, with 1702 upregulated and 1502 downregulated genes. Investigation revealed that approximately 312 DEGs were strongly enriched in hormone signaling, sugar metabolism, root development, and cell cycle-related pathways. Thus, they were selected for their possible involvement in adventitious rooting. However, the higher accumulation of ABA, ZR, and JA-me contents and the upregulation of their related genes, as well as the downregulation of sugar metabolism-related genes, lead to the inhibition of ARs. These results indicate that AR formation is a complicated biological process chiefly influenced by multiple hormonal signaling pathways and sugar metabolism. This is the first study to demonstrate how PEG inhibits AR formation in apple plants.

SiMYB19 from Foxtail Millet (Setaria italica) Confers Transgenic Rice Tolerance to High Salt Stress in the Field

Salt stress is a major threat to crop quality and yield. Most experiments on salt stress-related genes have been conducted at the laboratory or greenhouse scale. Consequently, there is a lack of research demonstrating the merit of exploring these genes in field crops. Here, we found that the R2R3-MYB transcription factor SiMYB19 from foxtail millet is expressed mainly in the roots and is induced by various abiotic stressors such as salt, drought, low nitrogen, and abscisic acid. SiMYB19 is tentatively localized to the nucleus and activates transcription. It enhances salt tolerance in transgenic rice at the germination and seedling stages. SiMYB19 overexpression increased shoot height, grain yield, and salt tolerance in field- and salt pond-grown transgenic rice. SiMYB19 overexpression promotes abscisic acid (ABA) accumulation in transgenic rice and upregulates the ABA synthesis gene OsNCED3 and the ABA signal transduction pathway-related genes OsPK1 and OsABF2. Thus, SiMYB19 improves salt tolerance in transgenic rice by regulating ABA synthesis and signal transduction. Using rice heterologous expression analysis, the present study introduced a novel candidate gene for improving salt tolerance and increasing yield in crops grown in saline-alkali soil.

Stress-associated developmental reprogramming in moss protonemata by synthetic activation of the common symbiosis pathway

SummarySymbioses between angiosperms and rhizobia or arbuscular mycorrhizal fungi are controlled through a conserved signaling pathway. Microbe-derived, chitin-based elicitors activate plant cell surface receptors and trigger nuclear calcium oscillations, which are decoded by a calcium/calmodulin-dependent protein kinase (CCaMK) and its target transcription factor interacting protein of DMI3 (IPD3). Genes encoding CCaMK and IPD3 have been lost in multiple non-mycorrhizal plant lineages yet retained among non-mycorrhizal mosses. Here, we demonstrated that the moss Physcomitrium is equipped with a bona fide CCaMK that can functionally complement a Medicago loss-of-function mutant. Conservation of regulatory phosphosites allowed us to generate predicted hyperactive forms of Physcomitrium CCaMK and IPD3. Overexpression of synthetically activated CCaMK or IPD3 in Physcomitrium led to abscisic acid (ABA) accumulation and ectopic development of brood cells, which are asexual propagules that facilitate escape from local abiotic stresses. We therefore propose a functional role for Physcomitrium CCaMK-IPD3 in stress-associated developmental reprogramming

Changes in the abscisic acid, phenylpropanoids and ascorbic acid metabolism during strawberry fruit growth and ripening

The functional compounds and sensory attributes of strawberries are acquired during ripening; however, the molecular mechanisms regulating this process have not yet been fully elucidated. Therefore, in this study, we aimed to investigate the accumulation of abscisic acid (ABA), phenylpropanoids, and l-ascorbic acid (AsA) as well as their relative gene expression levels during this process. The accumulation of ABA during the fruit growth and ripening stages depends on the upregulation of FaNCED1 and FaNCED2 gene expression, and the downregulation of FaCYP707 expression. Moreover, in the initial stages, the ABA glycosylation pathway is activated as a provision for the ABA levels required for future events. As the ABA levels increase, FaPAL, FaC4H1, and FaC4H4 genes expression are upregulated, aiding in the synthesis of flavonoid precursors, which, in addition to the higher FaUFGT expression, directly reflects an improvement in anthocyanin. AsA content increases during fruit development and ripening and is dependent on the synthesis pathway, due to the upregulation of FaGLDH expression, and on the oxidation and recycling pathways via the regulation of expression levels of FaAPX and FaMR. These results suggest that the activation of FaNCED1 and the inhibition of FaCYP707A1 may contribute to the increase in ABA content, thereby stimulating anthocyanin and AsA synthesis and accumulation.

The action of RED light: Specific elevation of pelargonidin-based anthocyanin through ABA-related pathway in strawberry

Light exposure could trigger a series of physiological progress in strawberry and influence the commercial values. In the present study, the red-light irradiation promoted the red coloration of postharvest strawberry, combined with the doubled content of pelargonidin-based anthocyanins. Alternatively, no significant difference was found in cyanidin- and peonidin-based anthocyanin compounds between control and red-light-exposed strawberry. Additionally, it was evident at the transcriptional level that red light induced more flux into the pelargonidin-based side branch, rather than into the cyanidin and peonidin-based branches. Besides, genes involved in abscisic acid (ABA) biosynthesis and deglycosylation were upregulated, while those in ABA hydroxylation and glycosylation were downregulated, resulting in the increased ABA accumulation by red light. The expression level of ABA downstream effector, FaMYB10, was also upregulated, probably responsible for the precise regulation of anthocyanin biosynthesis. These findings shed light on the potential role of red-light exposure on the pelargonidin-based anthocyanin accumulation through the ABA-related pathway in strawberry.

Comparative transcriptomic analysis on compatible/incompatible grafts in citrus.

Grafting is a useful cultivation technology to resist abiotic and biotic stresses and is an integral part of citrus production. However, some widely utilized rootstocks may still exhibit graft incompatibility in the orchard. ‘Hongmian miyou’ (Citrus maxima (Burm.) Merrill) is mutated from ‘Guanxi miyou’, but these two scions showed different compatibility with available Poncirus trifoliata rootstock. Foliage etiolation is an observed symptom of graft incompatibility, but its mechanism remains poorly understood. This study is the first to investigate the morphological, physiological, and anatomical differences between compatible and incompatible grafts, and perform transcriptome profiling at crucial stages of the foliage etiolation process. Based on comprehensive analyses, hormonal balance was disordered, and two rate-limiting genes, NCED3 (9-cis-epoxycarotenoid dioxygenase 3) and NCED5, being responsible for ABA (abscisic acid) accumulation, were highlighted. Further correlation analysis indicated that IAA (indole-3-acetic acid) and ABA were the most likely inducers of the expression of stress-related genes. In addition, excessive starch accumulation was observed in the lamina and midribs of leaves of incompatible grafts. These results provide a new insight into the role of hormonal balance and ABA biosynthesis genes in regulating and contributing to graft incompatibility, and will further define and deploy candidate genes to explore the mechanisms underlying citrus rootstock–scion interactions.

Long-distance control of pumpkin rootstock over cucumber scion under drought stress as revealed by transcriptome sequencing and mobile mRNAs identifications.

Grafting with pumpkin rootstock is commonly used not only to improve the quality of cucumber fruits but also to confer biotic or abiotic stress tolerance. However, the molecular mechanism of the response of grafted cucumbers to drought stress and the possible roles of mobile mRNAs in improving stress tolerance have remained obscure. Hence, we conducted transcriptome sequencing and combined it with morphophysiological experiments to compare the response of homografts (cucumber as scion and rootstock) and heterografts (cucumber as scion and pumpkin as rootstock) to drought stress. After applying drought stress, homografts and heterografts expressed 2960 and 3088 genes, respectively, in response to the stress. The differentially expressed genes identified in heterografts under drought stress were categorized into different stress-responsive groups, such as carbohydrate metabolism (involved in osmotic adjustment by sugar accumulation), lipid and cell wall metabolism (involved in cell membrane integrity by a reduction in lipid peroxidation), redox homeostasis (increased antioxidant enzyme activities), phytohormone (increased abscisic acid content), protein kinases, and transcription factors, using MapMan software. Earlier and greater H2O2 accumulation in xylem below the graft union was accompanied by leaf abscisic acid accumulation in heterografts in response to drought stress. Greater leaf abscisic acid helped heterografted cucumbers to sense and respond to drought stress earlier than homografts. The timely response of heterografts to drought stress led to the maintenance of higher water content in the leaves even in the late stage of drought stress. The mobile mRNAs identified in heterografts were mostly related to photosynthesis, which would be the possible reason for improved chlorophyll content and maximum photochemical efficiency of photosystem II (Fv/Fm). The existence of some stress-responsive pumpkin (rootstock) mRNAs in cucumber (scion), such as heat shock protein (HSP70, a well-known stress-responsive gene), led to higher proline accumulation than in homografts. Expression of mobile and immobile stress-responsive mRNAs and timely response of heterografts to drought stress could improve drought tolerance in pumpkin-rooted plants.

Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

Plant physiological responses to various stresses are characterized by interaction and coupling, while the intrinsic mechanism remains unclear. The effects of intraspecific competition on plant growth, stomatal opening, and hormone concentrations were investigated with three tomato genotypes (WT-wild type, Ailsa Craig; FL-a abscisic acid (ABA) deficient mutant, flacca; NR-a partially ethylene-insensitive genotype) under two water regimes (full irrigation, irrigation amount = daily transpiration; deficit irrigation, 60% of irrigation amount in full irrigation) in this study. Three kinds of competitions were designed, i.e., root and canopy competition, non-root competition, and non-canopy competition, respectively. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato, accompanied by ABA accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in FL and NR, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. The absence of canopy competition insignificantly influenced plant stomatal opening of well-watered tomato, as canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, the absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbor detection signals maybe enhanced by soil drought. The absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

Contrasting responses to drought stress between <i>Chrysanthemum japonense</i> and <i>C. nankingense</i>

The response of <italic>Chrysanthemum japonense</italic> and <italic>C. nankingense</italic> to drought stress induced by polyethylene glycol was characterized at the level of leaf water status, leaf surface morphology and cuticular wax (quantity and composition), the activity of antioxidant enzymes, the extent of membrane lipid peroxidation, the accumulation of proline, photosynthesis performance and abscisic acid (ABA) accumulation. The more tolerant species <italic>C. japonense</italic> maintained its water status more effectively than <italic>C. nankingense</italic>, probably because its leaves form more cuticular wax and are able to accumulate higher levels of ABA. Superoxide dismutase activity was higher in <italic>C. japonense</italic> than in<italic> C. nankingense</italic>, as was that of catalase and ascorbate peroxidase during the later part of the stress episode, but levels of peroxidase were not differentiated at the end of the stress period. Membrane damage, as measured by electrolyte leakage and malondialdehyde accumulation, was less severe in <italic>C. japonense,</italic> which was also able to generate higher levels of free proline after a ten hour exposure to stress. Thus the superior response of <italic>C. japonense</italic> also reflects a more adapted system of osmoprotection and antioxidation. As a result, photosynthesis was compromised less by drought stress in <italic>C. japonense</italic> than in <italic>C. nankingense.</italic> That provides a scientific basis for the development and application of drought tolerance resources of chrysanthemum.

EFFECT OF DROUGHT ON MORPHOPHYSIOLOGICAL TRAITS OF RICE: A REVIEW

Drought is the condition of prolonged paucity in the water supply, whether atmospheric, surface water, or groundwater. This significant abiotic stress is a severe limiting factor of plant growth and rice productivity, adversely affecting the economic rice production globally. Drought stress has a considerable effect on the rice plant’s morphological and physiological traits preventing it from reaching the maximum yield. Morphological alteration in rice includes inhibition of seed germination, reduced tillers, early maturity, reduced biomass while physiological changes involve restricted cell division and elongation, stomatal closure, loss of turgor adjustment, lower photosynthesis, slower growth rate, yield reduction, etc. The stress further brings about a biochemical change by accumulating stress metabolites, increasing Reactive Oxygen Species (ROS) accumulations, increasing antioxidative enzymes and, Abscisic acid (ABA) accumulation. Various mitigation measures are applied to adhere to the effect of drought on rice plants by selecting drought-tolerant cultivars, planting early varieties, sufficient moisture maintenance, conventional breeding, molecular maintenance, and development of varieties with high yielding attributes. Thus, this review aims to assess the complex responses of rice plants to drought in morpho-physiological characters of rice along with its mitigation strategies in adoption to drought stress.

Difference Between Coloration and Endogenous Abscisic Acid Accumulation Patterns in Two Red Grape Cultivars, ‘Aki Queen’ and ‘Ruby Roman’ (&lt;i&gt;Vitis labruscana&lt;/i&gt; Bailey) Berries

Changes in anthocyanin and endogenous abscisic acid (ABA) contents in the berry skins of Vitis labruscana × V. vinifera cultivars, ‘Aki Queen’, and ‘Ruby Roman’ were investigated during the fruit development period. Color development of ‘Aki Queen’ berries mainly occurred within 20 days post véraison, while that of the ‘Ruby Roman’ was prolonged for about 40 days. In both cultivars, the ABA level in the berry skin started to increase a few days before véraison; however, ABA accumulation ceased approximately 10 days after véraison in ‘Aki Queen’, while it continued until the late stage of maturation in ‘Ruby Roman’. In addition, higher indole-3-acetate aspartate (IAA-Asp) and lower isopentenyladenine (iP) contents were observed in ‘Ruby Roman’ than in ‘Aki Queen’ at the late development stage. The expression analysis of genes involved in ABA metabolism revealed that V. vinifera 9-cis-epoxycarotenoid dioxygenase 3 (VviNCED3), which is assumed to play a major role in ABA biosynthesis, remained relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison. Considering that ABA plays a regulatory role in grape maturation, these results may indicate that the coloration of ‘Ruby Roman’ at the later stage of maturation is partly attributable to an increased ABA pool in berry skins.

Rice Glycosyltransferase Gene UGT85E1 Is Involved in Drought Stress Tolerance Through Enhancing Abscisic Acid Response.

Drought is one of the most important environmental constraints affecting plant growth and development and ultimately leads to yield loss. Uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs) are believed to play key roles in coping with environmental stresses. In rice, it is estimated that there are more than 200 UGT genes. However, most of them have not been identified as their physiological significance. In this study, we reported the characterization of a putative glycosyltransferase gene UGT85E1 in rice. UGT85E1 gene is significantly upregulated by drought stress and abscisic acid (ABA) treatment. The overexpression of UGT85E1 led to an enhanced tolerance in transgenic rice plants to drought stress, while the ugt85e1 mutants of rice showed a more sensitive phenotype to drought stress. Further studies indicated that UGT85E1 overexpression induced ABA accumulation, stomatal closure, enhanced reactive oxygen species (ROS) scavenging capacity, increased proline and sugar contents, and upregulated expression of stress-related genes under drought stress conditions. Moreover, when UGT85E1 was ectopically overexpressed in Arabidopsis, the transgenic plants showed increased tolerance to drought as well as in rice. Our findings suggest that UGT85E1 plays an important role in mediating plant response to drought and oxidative stresses. This work may provide a promising candidate gene for cultivating drought-tolerant crops both in dicots and monocots.

Abscisic Acid Mediates Grafting-Induced Cold Tolerance of Watermelon via Interaction With Melatonin and Methyl Jasmonate.

Grafting is widely used to increase plant defense responses to various stresses. Grafting-induced cold tolerance is associated with the increase of the antioxidant potential of plants; however, the underlying mechanisms remain unclear. Here, we found that pumpkin rootstocks promote antioxidant enzyme activities and alleviate cold-induced oxidative damage, accompanied by increased abscisic acid (ABA), melatonin, and methyl jasmonate (MeJA) levels in leaves. Increased ABA accumulation in leaves was attributed partly to the increased ABA levels in rootstocks. ABA induced antioxidant enzymes activities and the accumulation of melatonin and MeJA, while inhibition of ABA synthesis blocked the rootstock-induced antioxidant activity and the accumulation of melatonin and MeJA under cold stress. Melatonin and MeJA application also enhanced ABA accumulation in leaves after cold exposure, whereas inhibition of melatonin or MeJA synthesis attenuated the rootstock-induced increase of ABA. Moreover, melatonin and MeJA application alleviated cold-induced oxidative stress, but inhibition of melatonin or MeJA synthesis lowered the rootstock- or ABA-induced antioxidant potential and tolerance to cold. These findings indicate that ABA plays an important role in the grafting-induced cold tolerance by promoting the accumulation of melatonin and MeJA, which in turn, promote ABA accumulation, forming a positive feedback loop.

Expression Analysis of Mitogen-Activated Protein Kinases (MAPKs) Gene Family in Grapevine Berries

Plants, as sessile living organisms, are dependent on signalling mechanisms. Mitogen-activated protein kinases (MAPKs) are a highly conserved gene family that take a role in switching an extracellular signal into an intercellular signal. Ripening-related processes in non-climacteric fruits are not as well understood as in climacteric fruits. In this regard, studying MAPKs in grape berries during developmental stages may lead to a better understanding of physiological interactions during commercially relevant stages, such as pigmentation, ripening, and phenolics accumulation in the berries. Each MAPK cascade involves three or four MAPK proteins that facilitate signal transduction by phosphorylation of downstream targets. We examined the relative expression of VvMAP2Ks and VvMAP4Ks in berries at two-weekly intervals, from flowering to over-ripening. Expression analysis of 5 MAP2Ks and 7 MAP4Ks suggested that both gene families may play an active role in development of berries. Expression of VvMAP2K1 showed a correlation with abscisic acid (ABA) and ethylene accumulation. Moreover, the expression pattern of VvMAP2K2 and VvMAP2K3 shows a correlation with auxin, and ABA accumulation respectively. Furthermore, VvMAP2K4 may have a role in berry size increment and halting stomatal development. In addition, VvMAP2K5 may play a role in floral organ development. VvMAP4Ks expression pattern moves them forward to be excellent markers for monitoring the effect of for instance climate changerelated stress on berry development.

The involvement of abscisic acid in glucose promoted adventitious root development in cucumber

Several lines of evidence suggest that glucose (Glc) and abscisic acid (ABA) are important signal molecules involved in plant growth and development. In the study, cucumber (Cucumis sativus ‘Xinchun NO. 4′) was used to understand the roles and relationships of Glc and ABA in adventitious root development. The results show that the effect of Glc and ABA on adventitious rooting in cucumber was dose-dependent, with a maximal biological response at 0.10 mM Glc and 0.05 μM ABA, respectively. However, the promotive roles of Glc in adventitious rooting were suppressed by ABA inhibitor fluridone (FLU), suggesting that endogenous ABA might be involved in Glc-induced adventitious rooting. Glc increased endogenous ABA content and the activity of ABA biosynthesis-related enzyme zeaxanthin epoxidase (ZEP), 9-cis-epoxy-carotenoid dioxigenase (NCED) and aldehyde oxidase (AO) during adventitious rooting. Glc decreased the activity of ABA degradation-related enzyme ABA 8′-hydroxylase (ABA8’-H). Glc significantly up-regulated the expression of ABA biosynthesis-related genes CsNCED1 and CsNCED2 and ABA signal transduction-related genes CsPYR1, CsPYR2, CsPYL8 and CsSRK2E, and significantly down-regulated the expression of ABA degradation-related genes CsCYP707A1 and CsCYP707A2. However, Glc-enhanced ABA content, ABA-related enzyme activity and ABA-related gene expression were reversed by FLU. Therefore, Glc might promote adventitious rooting by enhancing ABA accumulation, in which the activity of ABA biosynthesis enzyme (ZEP, NCED and AO), the expression of ABA biosynthesis-related genes (CsNCED1 and CsNCED2) and ABA signal transduction-related genes (CsPYR1, CsPYR2, CsPYL8 and CsSRK2E) were increased by Glc, and the activity of ABA degradation enzyme ABA8’-H and the expression of ABA degradation-related genes (CsCYP707A1 and CsCYP707A2) were inhibited by Glc.

Formation of resting cells is accompanied with enrichment of ferritin in marine diatom Phaeodactylum tricornutum

The formation of resting cells/spores in marine diatoms helps them to survive in environmental changes, whose sedimentation characteristics also drive enhanced carbon fluxes export to the deep ocean. However, the molecular mechanism underlying the transformation remains unclear. Based on the upregulation of ferritin during dormancy in microorganism and its' crucial role in coping with environmental stress, we constructed the ferritin overexpression and silence strains in model marine diatom, Phaeodactylum tricornutum (FTN-OE and FTNSi, respectively). The morphological transformation from fusiform to ovoid were observed among the FTN-OE strains but not the wide type and FTN-Si strains. These FTN-OE oval cells exhibited typical characteristics of resting cells and benthic adaptation, such as lower growth rates, low-light adaptation, silicified valves, the excretion of exopolymeric substances, upregulation of stress-resistant proteins and increased nitrate reserves. Furthermore, FTN-OE oval cells showed increased abscisic acid synthesis and signaling pathways in the transcriptome and proteome. And the abscisic acid signal was detected in FTN-OE oval cells exclusively (2.96 ng g−1 FW), but absent in the FTNSi, FTN-OE fusiform or WT cells. Overall, our results demonstrate that ferritin overexpression in marine diatom have a close relationship with morphological transformation from fusiform to ovoid morphotype, after which they enter a resting stage, which is accompanied by abscisic acid accumulation. This improves our understanding of the molecular processes in diatom resting cells/spores' formation and suggests that ferritin accumulation might improve the sequestration of photosynthetically fixed atmospheric CO2 into the deep sea.

Putrescine regulates stomatal opening of cucumber leaves under salt stress via the H2O2-mediated signaling pathway

The stomatal aperture is imperative for photosynthesis in higher plants. The function of polyamines (PAs) in stomatal regulation under a stressful environment has not been fully determined. In this study, we demonstrated the mechanism by which putrescine (Put) regulates stomatal changes in cucumber leaves under salt stress. The results showed that foliar application of Put alleviated the decrease of stomatal aperture and photosynthesis caused by salt stress and promoted plant growth. Exogenous Put caused a significant increase in endogenous PAs and hydrogen peroxide (H2O2) levels by 105.43% and 27.97%, respectively, while decreased abscisic acid (ABA) content by 67.68% under salt stress. However, application of inhibitors of aminoguanidine hydrochloride (AG), 1, 8-diaminooctane (1, 8-DO), diphenyleneiodonium chloride (DPI) and salicylhydroxamic acid (SHAM) upregulated the 9-cis-cyclocarotenoid dioxygenase (NCED) gene and downregulated the reduced glutathione synthetase (GSHS) gene. These inhibitors also decreased the stomatal aperture, levels of H2O2 and reduced glutathione (GSH), but increased the ABA content under salt stress and Put treatment conditions. The order of influence is AG > 1, 8-DO > DPI > SHAM. However, Put-induced downregulation of ABA content and upregulation of GSH content under salt stress were effectively blocked by N, N′-dimethylthiourea (DMTU, H2O2 scavenger) and 1-chloro-2,4-dinitrobenzene (CDNB, GSH scavenger) treatments. Taken together, these results suggest that Put induced the formation of H2O2 signaling mediates the degradation of PAs by diamine oxidase (DAO), increasing GSH content and inhibiting the accumulation of ABA in leaves, thereby promoting stomatal opening in salt-stressed cucumber leaves.

Phospholipase Dα1 Acts as a Negative Regulator of High Mg2+-Induced Leaf Senescence in Arabidopsis.

Magnesium (Mg2+) is a macronutrient involved in essential cellular processes. Its deficiency or excess is a stress factor for plants, seriously affecting their growth and development and therefore, its accurate regulation is essential. Recently, we discovered that phospholipase Dα1 (PLDα1) activity is vital in the stress response to high-magnesium conditions in Arabidopsis roots. This study shows that PLDα1 acts as a negative regulator of high-Mg2+-induced leaf senescence in Arabidopsis. The level of phosphatidic acid produced by PLDα1 and the amount of PLDα1 in the leaves increase in plants treated with high Mg2+. A knockout mutant of PLDα1 (pldα1-1), exhibits premature leaf senescence under high-Mg2+ conditions. In pldα1-1 plants, higher accumulation of abscisic and jasmonic acid (JA) and impaired magnesium, potassium and phosphate homeostasis were observed under high-Mg2+ conditions. High Mg2+ also led to an increase of starch and proline content in Arabidopsis plants. While the starch content was higher in pldα1-1 plants, proline content was significantly lower in pldα1-1 compared with wild type plants. Our results show that PLDα1 is essential for Arabidopsis plants to cope with the pleiotropic effects of high-Mg2+ stress and delay the leaf senescence.