NCED Genes Research Articles

The overexpression of NCED results in waterlogging sensitivity in soybean

Soil waterlogging limits plant growth and has a major impact on agricultural productivity. Here, we tested the hypothesis that the overexpression of the NCED gene improves waterlogging and reoxygenation tolerance in soybean plants. This was tested using a transgenic soybean line overexpressing the NCED gene (2Ha11) and the conventional cultivar BRS184 (wild-type; WT), which is the genetic background of the 2Ha11 line. Plants at vegetative (V6) and reproductive (R2) stages were exposed to waterlogging for 60 h and posterior reoxygenation for an additional 60 h. Overall, the NCED overexpression increased the levels of lipid peroxidation in plants exposed to waterlogging and posterior reoxygenation while decreased the antioxidant activity and alcohol dehydrogenase activity. In addition, NCED overexpression decreased seed weight and grain yield in the 2Ha11 line exposed to waterlogging at the reproductive stage. Taken together, these results suggest that the overexpression of NCED triggers an increased waterlogging sensitivity in soybean plants especially when they are exposed to waterlogging at the reproductive stage.

Drought Stress-Mediated Transcriptome Profile Reveals NCED as a Key Player Modulating Drought Tolerance in Populus davidiana.

Populus trichocarpa has been studied as a model poplar species through biomolecular approaches and was the first tree species to be genome sequenced. In this study, we employed a high throughput RNA-sequencing (RNA-seq) mediated leaf transcriptome analysis to investigate the response of four different Populus davidiana cultivars to drought stress. Following the RNA-seq, we compared the transcriptome profiles and identified two differentially expressed genes (DEGs) with contrasting expression patterns in the drought-sensitive and tolerant groups, i.e., upregulated in the drought-tolerant P. davidiana groups but downregulated in the sensitive group. Both these genes encode a 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme required for abscisic acid (ABA) biosynthesis. The high-performance liquid chromatography (HPLC) measurements showed a significantly higher ABA accumulation in the cultivars of the drought-tolerant group following dehydration. The Arabidopsis nced3 loss-of-function mutants showed a significantly higher sensitivity to drought stress, ~90% of these plants died after 9 days of drought stress treatment. The real-time PCR analysis of several key genes indicated a strict regulation of drought stress at the transcriptional level in the P. davidiana drought-tolerant cultivars. The transgenic P. davidiana NCED3 overexpressing (OE) plants were significantly more tolerant to drought stress as compared with the NCED knock-down RNA interference (RNAi) lines. Further, the NCED OE plants accumulated a significantly higher quantity of ABA and exhibited strict regulation of drought stress at the transcriptional level. Furthermore, we identified several key differences in the amino acid sequence, predicted structure, and co-factor/ligand binding activity of NCED3 between drought-tolerant and susceptible P. davidiana cultivars. Here, we presented the first evidence of the significant role of NCED genes in regulating ABA-dependent drought stress responses in the forest tree P. davidiana and uncovered the molecular basis of NCED3 evolution associated with increased drought tolerance.

Development of stable transgenic maize plants tolerant for drought by manipulating ABA signaling through Agrobacterium-mediated transformation

BackgroundIn crop plants, to cope up with the demand of food for rising population, revolutionary crop improvement programmes are being implemented for higher and higher yields. Abiotic stress, especially at flowering stage, causes drastic effect on yield in plants. Deforestation and urbanization made the water table very low and changed the climate which led to untimely and unforeseen rains which affect the yield of a crop through stress, both by lack of water as well as water logging (abiotic stress). Development of tolerant plants through breeding is a time-consuming programme and does not perform well in normal conditions. Development of stress-tolerant plants through transgenic technology is the better solution. Maize is a major crop used as food and fodder and has the commercial value in ethanol production. Hence, the genes viz., nced (9-cis-epoxycarotenoid dioxygenase) and rpk (receptor-like protein kinase), which play the key roles in the abscisic acid pathway and upstream component in ABA signaling have been transferred into maize plants through Agrobacterium-mediated transformation by optimizing several parameters to obtain maximum frequency of transformation. ResultsCultures raised from immature embryos of 2-mm size isolated from maize cobs, 12–15 days after pollination, were used for transformation. rpk and nced genes under the control of leaP and salT promoters respectively, cloned using gateway technology, have been introduced into elite maize inbred lines. Maximum frequency of transformation was observed with the callus infected after 20 days of inoculation by using 100 μM acetosyringone, 10 min infection time, and 2 days incubation period after co-cultivation resulted in maximum frequency of transformation (6%) in the NM5884 inbred line. Integration of the genes has been confirmed with molecular characterization by performing PCRs with marker as well as gene-specific primers and through southern hybridization. Physiological and biochemical characterization was done in vitro (artificial stress) and in vivo (pot experiments). ConclusionsChanges in the parameters which affect the transformation frequency yielded maximum frequency of transformation with 20-day-old callus in the NM5884 inbred line. Introducing two or more genes using gateway technology is useful for developing stable transgenic plants with desired characters, abiotic stress tolerance in this study.

Identification and functional analysis of 9-cis-epoxy carotenoid dioxygenase (NCED) homologs in G. hirsutum

9-cis-epoxy carotenoid dioxygenase (NCED) is a fundamental enzyme, which plays an essential role in the process of organ development and stress resistance by regulating abscisic acid (ABA) synthesis in plant. In this study, a total of 7, 7, 14 and 14 NCED genes were identified from the genomes of G. arboreum, G. raimondii, G. barbadense and G. hirsutum, respectively. Phylogenetic tree showed that all forty-two NCED genes could be classified into three groups in cotton genus. Collinear analysis revealed that the NCED genes in G. hirsutum were not amplified by tandem repeats after polyploidy events. The function of NCED genes was evaluated between two accessions with contrasting plant height. The results showed that expression of the NCED genes in dwarf accession was higher than that in taller ones. GhNCED1-silenced cotton plants confirmed that suppression of NCED genes could increase the plant height, but reduce the resistance abilities to drought and salt stress. Our study systematically identified the homologs of NCED genes and their functions in cotton, which could provide new genetic resources for improving plant height and stress in future cotton breeding.

Genome-wide identification and expression analysis of the NCED family in cotton (Gossypium hirsutum L.).

Abscisic acid (ABA) is an important plant hormone that plays multiple roles in regulating growth and development as well as in stress responses in plants. The NCED gene family includes key genes involved in the process of ABA synthesis. This gene family has been found in many species; however, the function of the NCED gene family in cotton is unclear. Here, a total of 23 NCED genes (designated as GhNCED1 to GhNCED23) were identified in cotton. Phylogenetic analysis indicated that the identified NCED proteins from cotton and Arabidopsis could be classified into 4 subgroups. Conserved motif analysis revealed that the gene structure and motif distribution of proteins within each subgroup were highly conserved. qRT-PCR and ABA content analyses indicated that NCED genes exhibited stage-specific expression patterns at tissue development stages. GhNCED5, GhNCED6 and GhNCED13 expression was similar to the change in ABA content, suggesting that this gene family plays a role in ABA synthesis. These results provide a better understanding of the potential functions of GhNCED genes.

Double NCED isozymes control ABA biosynthesis for ripening and senescent regulation in peach fruits

During ripening, peach fruits (Prunus persica L. Batsch) rapidly progress to the senescent stage, resulting in a brief shelf life. Abscisic acid (ABA) plays an important role in regulating the ripening process, both in climacteric and non-climacteric fruits. A key enzyme for ABA biosynthesis in higher plants is 9-cis-epoxycarotenoid dioxygenase (NCED). In this study, two NCED isozymes, PpNCED1 and PpNCED5, were identified in peach fruits. While both NCED genes had similar transcriptional patterns (up-regulation) at the beginning of peach ripening, PpNCED5 showed a consistently lower expression level than PpNCED1. During the post-harvest stage, gene expression of PpNCED1 declined, while PpNCED5 expression increased relative to PpNCED1 expression. Considering the dynamic process of ABA accumulation during fruit ripening and senescence in peach, this study indicates that both NCED genes cooperatively control ABA biosynthesis in peach fruits. Moreover, spatio-temporal expression and transcriptional response to hormone and abiotic stress suggested that there is functional divergence between PpNCED1 and PpNCED5 genes in peach. A carotenoid-rich callus system was used to verify the function of PpNCED1 and PpNCED5. In the transgenic callus system, both PpNCED1 and PpNCED5 isozymes promoted ABA biosynthesis, which likely accelerated cell senescence through activating ROS signals. The results from this study provide evidence supporting an ABA biosynthetic regulation process via the two NCED genes in peach fruit, and suggest a mechanism of ABA-induced fruit ripening and senescence.

Effects of simulated drought stress on carotenoid contents and expression of related genes in carrot taproots.

Carotenoids are liposoluble pigments found in plant chromoplasts that are responsible for the yellow, orange, and red colors of carrot taproots. Drought is one of the main stress factors affecting carrot growth. Carotenoids play important roles in drought resistance in higher plants. In the present work, the carotenoid contents in three different-colored carrot cultivars, 'Kurodagosun' (orange), 'Benhongjinshi' (red), and 'Qitouhuang' (yellow), were determined by ultra-high-performance liquid chromatography (UPLC) after 15% polyethylene glycol (PEG) 6000 treatment. Real-time fluorescence quantitative PCR (RT-qPCR) was then used to determine the expression levels of carotenoid synthesis- and degradation-related genes. Increases in β-carotene content in 'Qitouhuang' taproots under drought stress were found to be related to the expression levels of DcPSY2 and DcLCYB. Increases in lutein and decreases in α-carotene content in 'Qitouhuang' and 'Kurodagosun' under PEG treatment may be related to the expression levels of DcCYP97A3, DcCHXE, and DcCHXB1. The expression levels of DcNCED1 and DcNCED2 in the three cultivars significantly increased, thus suggesting that NCED genes could respond to drought stress. Analysis of the growth status and carotenoid contents of carrots under PEG treatment indicated that the orange cultivar 'Kurodagosun' has better adaptability to drought stress than the other cultivars and that β-carotene and lutein may be involved in the stress resistance process of carrot.

Co-regulation Role of Endogenous Hormones and Transcriptomics Profiling Under Cold Stress in Tetrastigma hemsleyanum

Tetrastigma hemsleyanum Diels et Gilg is a valuable medicinal herb. Chilling sensitivity is the major limiting factor of the artificial cultivation of the plant. Some key genes, such as ZEP and NCED genes of ABA biosynthesis, GA2ox, GA3ox, and GA20ox genes of GA biosynthesis, ACO genes of ET biosynthesis pathway were screened to be crucial in cold response. The response of ABA and ABA/GA1+3 to cold stress was prior to that of GA1+3, ZR, ABA/IAA, and ABA/ZR. The increasing changes in ABA/GA1+3 turned to a steep decline with the extension of stress time, which might be one factor contributing to cold sensitivity of T. hemsleyanum. The cold tolerance of T. hemsleyanum would be repressed by GA3 but enhanced by ABA when ABA orGA3 was used alone. Both the ABA-mediated promotion and GA-mediated repression of cold tolerance could be attenuated using a combination of the two phytohormones within 6 h. When the biosynthesis of ABA and GA were inhibited by FLU and PAC, respectively, the effects of GA and ABA treatment were reversed partially. In summary, we presented the first study of global hormone-regulated transcripts expression patterns in T. hemsleyanum. This study suggested that GA and ABA could work antagonistically to balance the cold stress responses. PAC, a GA biogenesis inhibitor, as well as exogenous ABA, might be potential plant growth regulators that can promote cold tolerance of T. hemsleyanum. The study also provided valuable hints in revealing the potential candidate genes that regulated cold tolerance of T. hemsleyanum.

Involvement of HD-ZIP I transcription factors LcHB2 and LcHB3 in fruitlet abscission by promoting transcription of genes related to the biosynthesis of ethylene and ABA in litchi.

Abnormal fruitlet abscission is a limiting factor in the production of litchi, an economically important fruit in Southern Asia. Both ethylene and abscisic acid (ABA) induce organ abscission in plants. Although ACS/ACO and NCED genes are known to encode key enzymes required for ethylene and ABA biosynthesis, respectively, the transcriptional regulation of these genes is unclear in the process of plant organ shedding. Here, two polygalacturonase (PG) genes (LcPG1 and LcPG2) and two novel homeodomain-leucine zipper I transcription factors genes (LcHB2 and LcHB3) were identified as key genes associated with the fruitlet abscission in litchi. The expression of LcPG1 and LcPG2 was strongly associated with litchi fruitlet abscission, consistent with enhanced PG activity and reduced homogalacturonan content in fruitlet abscission zones (FAZs). The promoter activities of LcPG1/2 were enhanced by ethephon and ABA. In addition, the production of ethylene and ABA in fruitlets was significantly increased during fruit abscission. Consistently, expression of five genes (LcACO2, LcACO3, LcACS1, LcACS4 and LcACS7) related to ethylene biosynthesis and one gene (LcNCED3) related to ABA biosynthesis in FAZs were activated. Further, electrophoretic mobility shift assays and transient expression experiments demonstrated that both LcHB2 and LcHB3 could directly bind to the promoter of LcACO2/3, LcACS1/4/7 and LcNCED3 genes and activate their expression. Collectively, we propose that LcHB2/3 are involved in the litchi fruitlet abscission through positive regulation of ethylene and ABA biosynthesis.

OsNCED5, a 9-cis-epoxycarotenoid dioxygenase gene, regulates salt and water stress tolerance and leaf senescence in rice

9-cis-epoxycarotenoid dioxygenase (NCED) is a rate-limiting enzyme for abscisic acid (ABA) biosynthesis. However, the molecular mechanisms of NCED5 that modulate plant development and abiotic stress tolerance are still unclear, particular in rice. Here, we demonstrate that a rice NCED gene, OsNCED5, was expressed in all tissues we tested, and was induced by exposure to salt stress, water stress, and darkness. Mutational analysis showed that nced5 mutants reduced ABA level and decreased tolerance to salt and water stress and delayed leaf senescence. However, OsNCED5 overexpression increased ABA level, enhanced tolerance to the stresses, and accelerated leaf senescence. Transcript analysis showed that OsNCED5 regulated ABA-dependent abiotic stress and senescence-related gene expression. Additionally, ectopic expression of OsNCED5 tested in Arabidopsis thaliana altered plant size and leaf morphology and delayed seed germination and flowering time. Thus, OsNCED5 may regulate plant development and stress resistance through control of ABA biosynthesis. These findings contribute to our understanding of the molecular mechanisms by which NCED regulates plant development and responses to abiotic stress in different crop species.

Cytokinin-induced parthenocarpy of San Pedro type fig (Ficus carica L.) main crop: explained by phytohormone assay and transcriptomic network comparison.

CPPU-induced San Pedro type fig main crop parthenocarpy exhibited constantly increasing IAA content and more significantly enriched KEGG pathways in the receptacle than in female flowers. N-(2-chloro-4-pyridyl)-N-phenylurea (CPPU) was applied to San Pedro fig (Ficus carica L.) main crop to induce parthenocarpy; the optimal effect was obtained with 25mgL-1 application to syconia when female flowers were at anthesis. To elucidate the key expression changes in parthenocarpy conversion, significant changes in phytohormone level and transcriptome of fig female flowers and receptacles were monitored. HPLC-MS revealed increased IAA content in female flowers and receptacle 2, 4 and 10days after treatment (DAT), decreased zeatin level in the receptacle 2, 4 and 10 DAT, decreased GA3 content 2 and 4 DAT, and increased GA3 content 10 DAT. ABA level increased 2 and 4 DAT, and decreased 10 DAT. CPPU-treated syconia released more ethylene than the control except 2 DAT. RNA-Seq and bioinformatics analysis revealed notably more differentially expressed KEGG pathways in the receptacle than in female flowers. In the phytohormone gene network, GA-biosynthesis genes GA20ox and GA3ox were upregulated, along with GA signal-transduction genes GID1 and GID2, and IAA-signaling genes AUX/IAA and GH3. ABA-biosynthesis gene NCED and signaling genes PP2C and ABF were downregulated 10 DAT. One ACO gene showed consistent upregulation in both female flowers and receptacle after CPPU treatment, and more than a dozen of ERFs demonstrated opposing changes in expression. Our results revealed early-stage spatiotemporal phytohormone and transcriptomic responses in CPPU-induced San Pedro fig main crop parthenocarpy, which could be valuable for further understanding the nature of the parthenocarpy of different fig types.

Physiological, biochemical and molecular responses to water stress and rehydration in Mediterranean adapted tomato landraces.

Mediterranean tomato landraces adapted to arid environments represent an option to counteract drought, and to address the complexity of responses to water deficit and recovery, which is a crucial component of plant adaptation mechanisms. We investigated physiological, biochemical and molecular responses of two Mediterranean tomato landraces, 'Locale di Salina' (Lc) and 'Pizzutello di Sciacca' (Pz) under two dehydration periods and intermediate rehydration in greenhouse pot experiments. Relationship between CO2 assimilation (A) and stomatal conductance under severe water stress (gs <0.05mol·m-2 ·s-1 ) indicated the occurrence of stomatal and non-stomatal limitations of photosynthesis. Gas exchange promptly recovered within 2-3days of rehydration. ABA and gs showed a strict exponential relationship. Both leaf ABA and proline peaked under severe water stress. Lc showed higher accumulation of ABA and higher induction of the expression of both NCED and P5CS genes than Pz. Poly(ADP-ribose) polymerase increased during imposition of stress, mainly in Lc, and decreased under severe water stress. The two landraces hardly differed in their physiological performance. Under severe water stress, gs showed low sensitivity to ABA, which instead controlled stomatal closure under moderate water stress (gs >0.15mol·m-2 ·s-1 ). The prompt recovery after rehydration of both landraces confirmed their drought-tolerant behaviour. Differences between the two landraces were instead observed at biochemical and molecular levels.

Cloning and expression analysis of the FvNCED3 gene and its promoter from ash (Fraxinus velutina)

The 9-cis-epoxycarotenoid dioxygenase (NCED) gene is rate-limiting in abscisic acid (ABA) biosynthesis. In this study, an NCED gene, designated FvNCED3 (KY008746), was cloned from velvet ash (Fraxinus velutina Torr.) with a RACE method. The full length cDNA of FvNCED3 encodes a 573-amino acid polypeptide. Sequencing analysis showed that the FvNCED3 protein was highly homologous to other NCED proteins. The expression patterns of FvNCED3 in different ash organs were analyzed by real-time PCR which revealed that FvNCED3 expression levels were highest in leaves and lowest in roots. The gene expression patterns of FvNCED3 under abiotic stress indicated that its expression increased under drought, salt and ABA stress and decreased due to high and low temperatures. There were no obvious changes under ultraviolet light. The 1094-bp upstream sequence 5′ flank regulation region of the FvNCED3 gene was also cloned from ash using the Genome Walking method. To assess the activity of the FvNCED3 promoter, a pFvNCED3p::GUS plant expression vector was constructed for tobacco transformation. GUS expression of the FvNCED3 GUS enzyme activity was detected in almost all transgenic tobacco tissues, especially in the young leaves, stigma, anther, ovule and ovary. After treating the transgenic tobacco with NaCl and placing it under drought stress, GUS staining of tobacco leaves increased compared with that under normal growth conditions. This result indicates that gene expression driven by the FvNCED3 promoter can be induced by salt and drought stress.

Research Article Differential expression of dormancy-Associated genes in fastigiata and hypogaea peanut

Seed dormancy is a temporary replacement state observed in some higher plants, which prevents germination under unfavorable conditions. In several species, dormancy process is triggered by hormonal factors, initiated by ABA and precursor enzymes. In this work, we investigated the relationship between dormancy and the expression of ARP, DMR1, and NCED genes in upright and runner peanut seeds. Eight dormancy-contrasting genotypes were previously phenotyped based on germination traits, during three storage periods. Expression of ARP, DMR1 and NCED transcripts was analyzed by qRT-PCR, from endosperm and embryo tissues. Higher expression of NCED and ARP were found in embryo tissues from runner genotypes, IAC Caiapo and LGoPE-06, confirming findings in literature as to association of these genes with seed dormancy. Higher expression of DMR1 was found only in endosperm of upright materials (L7 Bege and BR1). We suggest the NCED is a functional molecular marker to identify dormancy in seeds, contributing to selection procedures of runner genotypes in peanut breeding.

Expression of NCED gene in colored cotton genotypes subjected to water stress

ABSTRACT Considering that the NCED gene acts on the biosynthetic cascade of ABA, a hormone involved in the functioning of stomata and consequently in the regulation of transpiration, the aim of this research was to analyze the expression of this gene in colored cotton genotypes subjected to water stress at the beginning of plant growth. Four colored cotton genotypes were used, subjected to two managements, with and without water stress, beginning the treatments when the blade of the first true leaves reached an area that allowed the evaluation of gas exchange. For the studies of the expression of the NCED gene, via RT-qPCR, leaves were collected on three distinct dates: at 4 and 6 days of water stress, and after the plants regained their turgor. The differential expression of NCED was found in all genotypes, with higher levels of expression related to six days of water stress. When the stomatal conductance was around 25%, there was overexpression in the genotype CNPA 2009.13, followed by CNPA 2009.6, BRS SAFIRA and CNPA 2009.11, confirming the data obtained in the semi-quantitative RT-PCR. The NCED gene is involved in the response to water stress in the vegetative phase of colored cotton.

Loss of heterophylly in aquatic plants: not ABA-mediated stress but exogenous ABA treatment induces stomatal leaves in Potamogeton perfoliatus.

Heterophyllous aquatic plants produce aerial (i.e., floating and terrestrial) and submerged leaves—the latter lack stomata—while homophyllous plants contain only submerged leaves, and cannot survive on land. To identify whether differences in morphogenetic potential and/or physiological stress responses are responsible for variation in phenotypic plasticity between two plants types, responses to abscisic acid (ABA) and salinity stress were compared between the closely related, but ecologically diverse pondweeds, Potamogeton wrightii (heterophyllous) and P. perfoliatus (homophyllous). The ABA-treated (1 or 10 μM) P. wrightii plants exhibited heterophylly and produced leaves with stomata. The obligate submerged P. perfoliatus plants were able to produce stomata on their leaves, but there were no changes to leaf shape, and stomatal production occurred only at a high ABA concentration (10 μM). Under salinity stress conditions, only P. wrightii leaves formed stomata. Additionally, the expression of stress-responsive NCED genes, which encode a key enzyme in ABA biosynthesis, was consistently up-regulated in P. wrightii, but only temporarily in P. perfoliatus. The observed species-specific gene expression patterns may be responsible for the induction or suppression of stomatal production during exposure to salinity stress. These results suggest that the two Potamogeton species have an innate morphogenetic ability to form stomata, but the actual production of stomata depends on ABA-mediated stress responses specific to each species and habitat.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-016-0844-x) contains supplementary material, which is available to authorized users.

Abscisic acid metabolic genes of wheat (Triticum aestivum L.): identification and insights into their functionality in seed dormancy and dehydration tolerance.

The three homeologues of wheat NCED2 were identified; the wheat NCED2A and CYP707A1B affect seed ABA level and dormancy but not leaf ABA level and transpirational water loss in Arabidopsis. Biosynthesis and catabolism of abscisic acid (ABA) in plants are primarily regulated by 9-cis-epoxycarotenoid dioxygenases (NCEDs) and ABA 8'-hydroxylase (ABA8'OH), respectively. The present study identified the complete coding sequences of a second NCED gene, designated as TaNCED2, and its homeologues (TaNCED2A, TaNCED2B and TaNCED2D) in hexaploid wheat, and characterized its functionality in seed dormancy and leaf dehydration tolerance using the TaNCED2A homeologue. The study also investigated the role of the B genome copy of the cytochrome P450 monooxygenase 707A1 (CYP707A1) gene of hexaploid wheat (TaCYP707A1B), which encodes ABA8'OH, in regulating the two traits as this has not been studied before. Ectopic expression of TaNCED2A and TaCYP707A1B in Arabidopsis resulted in altered seed ABA level and dormancy with no effect on leaf ABA content and transpirational water loss. To gain insights into the physiological roles of TaNCED2 and TaCYP707A1 in wheat, the study examined their spatiotemporal expression patterns and determined the genomic contributions of transcripts to their total expression.

H2O2 and ABA signaling are responsible for the increased Na+ efflux and water uptake in Gossypium hirsutum L. roots in the non-saline side under non-uniform root zone salinity.

Non-uniform root salinity increases the Na(+)efflux, water use, and growth of the root in non-saline side, which may be regulated by some form of signaling induced by the high-salinity side. However, the signaling and its specific function have remained unknown. Using a split-root system to simulate a non-uniform root zone salinity in Gossypium hirsutum L., we showed that the up-regulated expression of sodium efflux-related genes (SOS1, SOS2, PMA1, and PMA2) and water uptake-related genes (PIP1 and PIP2) was possibly involved in the elevated Na(+) efflux and water use in the the roots in the non-saline side. The increased level of indole acetic acid (IAA) in the non-saline side was the likely cause of the increased root growth. Also, the abscisic acid (ABA) and H2O2 contents in roots in the non-saline side increased, possibly due to the increased expression of their key biosynthesis genes, NCED and RBOHC, and the decreased expression of ABA catabolic CYP707A genes. Exogenous ABA added to the non-saline side induced H2O2 generation by up-regulating the RBOHC gene, but this was decreased by exogenous fluridone. Exogenous H2O2 added to the non-saline side reduced the ABA content by down-regulating NCED genes, which can be induced by diphenylene iodonium (DPI) treatment in the non-saline side, suggesting a feedback mechanism between ABA and H2O2.Both exogenous ABA and H2O2 enhanced the expression of SOS1, PIP1;7 ,PIP2;2, and PIP2;10 genes, but these were down-regulated by fluridone and DPI, suggesting that H2O2 and ABA are important signals for increasing root Na(+) efflux and water uptake in the roots in the non-saline side.

Stomatal responses to vapour pressure deficit are regulated by high speed gene expression in angiosperms.

Plants dynamically regulate water use by the movement of stomata on the surface of leaves. Stomatal responses to changes in vapour pressure deficit (VPD) are the principal regulator of daytime transpiration and water use efficiency in land plants. In angiosperms, stomatal responses to VPD appear to be regulated by the phytohormone abscisic acid (ABA), yet the origin of this ABA is controversial. After a 20 min exposure of plants, from three diverse angiosperm species, to a doubling in VPD, stomata closed, foliar ABA levels increased and the expression of the gene encoding the key, rate-limiting carotenoid cleavage enzyme (9-cis-epoxycarotenoid dioxygenase, NCED) in the ABA biosynthetic pathway was significantly up-regulated. The NCED gene was the only gene in the ABA biosynthetic pathway to be up-regulated over the short time scale corresponding to the response of stomata. The closure of stomata and rapid increase in foliar ABA levels could not be explained by the release of ABA from internal stores in the leaf or the hydrolysis of the conjugate ABA-glucose ester. These results implicate an extremely rapid de novo biosynthesis of ABA, mediated by a single gene, as the means by which angiosperm stomata respond to natural changes in VPD.

Water Stress Responses of Tomato Mutants Impaired in Hormone Biosynthesis Reveal Abscisic Acid, Jasmonic Acid and Salicylic Acid Interactions.

To investigate the putative crosstalk between JA and ABA in Solanum lycopersicum plants in response to drought, suppressor of prosystemin-mediated responses2 (spr2, JA-deficient) and flacca (flc, ABA-deficient) mutants together with the naphthalene/salicylate hydroxylase (NahG) transgenic (SA-deficient) line were used. Hormone profiling and gene expression of key enzymes in ABA, JA and SA biosynthesis were analyzed during early stages of drought. ABA accumulation was comparable in spr2 and wild type (WT) plants whereas expression of 9-cis-epoxycarotenoid dioxygenase 1 (NCED1) and NCED2 was different, implying a compensation mechanism between NCED genes and an organ-specific regulation of NCED1 expression. JA levels and 12-oxo-phytodienoic acid reductase 3 (OPR3) expression in flc plants suggest that ABA regulates the induction of the OPR3 gene in roots. By contrast, ABA treatment to flc plants leads to a reduction of JA and SA contents. Furthermore, different pattern of SA accumulation (and expression of isochorismate synthase and phenylalanine ammonia lyase 1) was observed between WT seedlings and mutants, suggesting that SA plays an important role on the early response of tomato plants to drought and also that JA and ABA modulate its biosynthesis. Finally, hormone profiling in spr2 and NahG plants indicate a crosstalk between JA and SA that could enhance tolerance of tomato to water stress.