ABA Levels Research Articles

Coordinate Responses of ABA Accumulation against Drought at Physiological, Ecological and Molecular Levels in <i>Triticum aestivum</i>

Much progress has been made toward understanding plant drought resistance. However, the coordinate responses of plant to drought on the basis of ABA level at physiological, ecological and molecular levels remains unclear. Here, the potted winter wheat (triticum aestivum) was cultivated under relative soil moisture (RSM ) respectively at 85% (well-watered), 65% (moderate stress), and 45% (severe stress), and a series of physiological and ecological parameters including ABA level, stomatal conductance, leaf temperature, leaf water potential, together with transcripts of ABA biosynthesis-metabolism key genes including9-cis-epoxycarotenoid dioxygenase(TaNCED),ABA glucosyltransferase(TaGT),ABA8'-hydroxylase(TaCYP707A), andβ-glucosidase(TaBG) were carried out. We found that ABA contents responsive to soil water loss increased rapidly and showed a significantly-negative correlation with the stomatal conductance and the leaf water potential and a significantly-positive correlation with the leaf-air temperature difference, respectively. The continuous accumulation of ABA was resulted mainly from the increased transcripts of bothTaNCEDsandTaBGsgenes. The transcripts ofTaCYP707A1andTaGTdeclined sharply from 85% to 65% RSM and then increased slightly from 65% to 45% RSM, indicating that ABA metabolism not only accelerates the accumulation of ABA level but also contributes to maintain ABA homeostasis. In conclusion, the macroscopic-microscopic changes responsive to water deficient reflects the ABA-regulated, drought-resistance coordinate mechanisms at physiological, ecological and molecular levels intriticum aestivum.

Transcriptome profiling identifies ABA mediated regulatory changes towards storage filling in developing seeds of castor bean (Ricinus communis L.).

BackgroundThe potential biodiesel plant castor bean (Ricinus communis) has been in the limelight for bioenergy research due to the availability of its genome which raises the bar for genome-wide studies claiming advances that impact the “genome-phenome challenge”. Here we report the application of phytohormone ABA as an exogenous factor for the improvement of storage reserve accumulation with a focus on the complex interaction of pathways associated with seed filling.ResultsAfter the application of exogenous ABA treatments, we measured an increased ABA levels in the developing seeds cultured in vitro using the ELISA technique and quantified the content of major biomolecules (including total lipids, sugars and protein) in treated seeds. Exogenous ABA (10 μM) enhanced the accumulation of soluble sugar content (6.3%) followed by deposition of total lipid content (4.9 %). To elucidate the possible ABA signal transduction pathways towards overall seed filling, we studied the differential gene expression analysis using Illumina RNA-Sequencing technology, resulting in 2568 (1507-up/1061-down regulated) differentially expressed genes were identified. These genes were involved in sugar metabolism (such as glucose-6-phosphate, fructose 1,6 bis-phosphate, glycerol-3-phosphate, pyruvate kinase), lipid biosynthesis (such as ACS, ACBP, GPAT2, GPAT3, FAD2, FAD3, SAD1 and DGAT1), storage proteins synthesis (such as SGP1, zinc finger protein, RING H2 protein, nodulin 55 and cytochrome P450), and ABA biosynthesis (such as NCED1, NCED3 and beta carotene). Further, we confirmed the validation of RNA-Sequencing data by Semi-quantitative RT-PCR analysis.ConclusionsTaken together, metabolite measurements supported by genes and pathway expression results indicated in this study provide new insights to understand the ABA signaling mechanism towards seed storage filling and also contribute useful information for facilitating oilseed crop functional genomics on an aim for utilizing castor bean agricultural and bioenergy use.

OsRACK1 is involved in abscisic acid- and H2O2-mediated signaling to regulate seed germination in rice (Oryza sativa, L.).

The receptor for activated C kinase 1 (RACK1) is one member of the most important WD repeat–containing family of proteins found in all eukaryotes and is involved in multiple signaling pathways. However, compared with the progress in the area of mammalian RACK1, our understanding of the functions and molecular mechanisms of RACK1 in the regulation of plant growth and development is still in its infancy. In the present study, we investigated the roles of rice RACK1A gene (OsRACK1A) in controlling seed germination and its molecular mechanisms by generating a series of transgenic rice lines, of which OsRACK1A was either over-expressed or under-expressed. Our results showed that OsRACK1A positively regulated seed germination and negatively regulated the responses of seed germination to both exogenous ABA and H2O2. Inhibition of ABA biosynthesis had no enhancing effect on germination, whereas inhibition of ABA catabolism significantly suppressed germination. ABA inhibition on seed germination was almost fully recovered by exogenous H2O2 treatment. Quantitative analyses showed that endogenous ABA levels were significantly higher and H2O2 levels significantly lower in OsRACK1A-down regulated transgenic lines as compared with those in wildtype or OsRACK1A-up regulated lines. Quantitative real-time PCR analyses showed that the transcript levels of OsRbohs and amylase genes, RAmy1A and RAmy3D, were significantly lower in OsRACK1A-down regulated transgenic lines. It is concluded that OsRACK1A positively regulates seed germination by controlling endogenous levels of ABA and H2O2 and their interaction.

Endogenous anti-β-glucan antibodies as a potential predictive biomarker for clinical response to imprime PGG immunotherapy in non-small cell lung cancer (NSCLC) patients.

3045 Background: Imprime PGG (IPGG) is a yeast-derived β-1,3/1,6 glucan that primes innate immune cells to kill antibody-targeted cancer cells via a complement receptor 3 (CR3)-dependent mechanism. In humans, naturally occurring anti-β-glucan antibodies (ABA) are required for binding of IPGG to CR3 and subsequent changes in innate cell functions. Methods: In a 32-donor healthy volunteer study, using a qualified quantitative ELISA assay, ABA levels and the threshold for binding and modulation of innate immune functions were evaluated, including a) complement activation, b) complement receptor expression, c) activation marker modulation, and d) selective chemokine production. The potential of the ABA level as a clinical biomarker for clinical response to IPGG was evaluated in a Phase 2 clinical trial by retrospectively segregating subjects into populations at or above the ABA threshold (biomarker positive; BM+) or below the ABA threshold (biomarker negative; BM-). Advanced NSCLC patients received cetuximab,...

Enhancement of neutrophil signaling and effector function by Imprime PGG in response to tumor cells in biomarker positive individuals (TUM7P.937)

Abstract Imprime PGG is a yeast β-glucan immunomodulator being developed for tumor therapy. Imprime PGG, in combination with tumor-specific monoclonal antibodies (MAb), is more effective in human trials than MAb therapy alone. Imprime PGG’s mechanism of action involves redirecting the innate immune system, in particular neutrophils, to kill MAb-targeted tumors cells. Recent work has identified a subset of individuals with high anti-β-glucan antibodies (ABA) that demonstrate greater efficacy to Imprime PGG treatment in vivo. Using ABA levels, we investigated signaling and functional differences in Imprime PGG treated neutrophils between biomarker positive and negative individuals. In this study we developed a calcium flux assay to assess Imprime PGG’s ability to modulate neutrophil signaling in response to MAb-targeted tumor cells. Our data demonstrates that ABA high individuals show a 3-fold greater enhancement in calcium signaling then ABA low individuals after Imprime PGG treatment. Functional activity was measured by Fc-mediated oxidative burst in response to antibody coated particles; a mechanism mimicking how antibody-coated tumor cells are recognized and eradicated by Imprime PGG treated neutrophils. ABA high individuals demonstrated a 5-fold greater enhancement in Fc-mediated oxidative burst upon Imprime PGG treatment then ABA low individuals. Our results demonstrate that Imprime PGG modulates signaling and functional activities in neutrophils of biomarker positive individuals.

Endogenous anti-β-glucan antibodies, a potential predictive biomarker for the efficacy of soluble yeast β-1,3/1,6 glucan (Imprime PGG®) immunotherapy in cancer patients (VAC3P.947)

Abstract The innate immune response to Imprime PGG® (Imprime PGG) is being leveraged to develop a novel cancer immunotherapy in conjunction with anti-tumor monoclonal antibodies. Previous research has demonstrated the presence of endogenous anti-β-glucan antibodies (ABA) as a necessary prerequisite for the binding and functional activity of Imprime PGG in innate immune cells. In this study, healthy donors with varying levels of ABA were evaluated to determine the threshold of ABA above which binding and modulation of functions were observed. Donors who had ABA levels above the threshold showed Imprime PGG binding (> 5%) to their neutrophils and monocytes with significant modulation of functions, including, a) activation of complement (C5a), b) increased surface expression of complement receptor 3, c) modulation of activation markers (CD62L), and d) production of selective chemokines (IL-8). The potential of the ABA level being a clinical biomarker was then evaluated in a non-small cell lung cancer trial by segregating patients into biomarker (BM) positive or negative populations based on the established ABA threshold. The BM positive patients showed a significantly increased objective response rate and marked survival benefit not seen in the BM negative patients. These results demonstrate a successful translation of biomarker discovery in healthy donors to clinical utility in cancer patients. ABA is a potential predictive biomarker for efficacy of Imprime PGG immunotherapy.

Response of stomatal conductance of two tree species to vapor pressure deficit in three climate zones

Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit (VPD) or relative humidity (RH) has been inadequately understood till now. In this study, responses of stomatal conduc- tance (gs) to VPD in two species of trees (Fraxinus chinensis Roxb., Populus alba L. var. pyramidalis Bge.) in three different climate zones (Jinan with typical warm humid/semi-humid climate, Urumqi with temperate continental arid climate and Turpan with extreme arid desert climate) were measured. Levels of two phytohormones (abscisic acid, ABA; indole-3-acetic acid, IAA) in the leaves of the two tree species at these three sites were also measured by high performance liquid chromatography. The results showed that the responses of gs to an increasing VPD in these two tree species at the three sites had peak curves which could be fitted with a Log Normal Model (gs=a·exp(-0.5(ln(D/c)/b) 2 ). The VPD/RH values corresponding to the maximum gs can be calculated using the fitting models for the two tree species in the three sites. We found that the calculated gs-max-VPD correlated nega- tively with relative air humidity in the three sites during the plant growth period (April to October 2010), which showed the values of gs-max-VPD were related to the climate conditions. The prevailing empirical stomatal model (Leuning model) and optimal stomatal behavior model could not properly simulate our measured data. The water use efficiency in the two tree species did not show obvious differences under three very different climatic conditions, but the highest gs, photosynthetic and transpiration rates occurred in P. alba var. of Turpan. The sensitivity in re- sponse of gs to VPD in leaves of the two trees showed positive correlations with the concentration of ABA, which implied that ABA level could be used as an indicator of the sensitivity of stomatal response to VPD. Our results confirmed that the prediction of the response of gs to VPD might be incomplete in the two current popular models. Therefore, an improved gs model which is able to integrate the results is needed. Also, the stomatal response mechanism of single peak curves of gs to VPD should be considered.

A transcriptional approach to unravel the connection between phospholipases A2 and D and ABA signal in citrus under water stress

The effect of water stress on the interplay between phospholipases (PL) A2 and D and ABA signalling was investigated in fruit and leaves from the sweet orange Navelate and its fruit-specific ABA-deficient mutant Pinalate by studying simultaneously expression of 5 PLD and 3 PLA2-encoding genes. In general, expression levels of PLD-encoding genes were higher at harvest in the flavedo (coloured outer part of the peel) from Pinalate. Moreover, a higher and transient increase in expression of CsPLDα, CsPLDβ, CsPLDδ and CsPLDζ was observed in the mutant as compared to Navelate fruit under water stress, which may reflect a mechanism of acclimation to water stress influenced by ABA deficiency. An early induction in CsPLDγ gene expression, when increase in peel damage during fruit storage was most evident, suggested a role for this gene in membrane degradation processes during water stress. Exogenous ABA on mutant fruit modified the expression of all PLD genes and reduced the expression of CsPLDα and CsPLDβ by 1 week to levels similar to those of Navelate, suggesting a repressor role of ABA on these genes. In general, CssPLA2α and β transcript levels were lower in flavedo from Pinalate than from Navelate fruit during the first 3 weeks of storage, suggesting that expression of these genes also depends at least partially on ABA levels. Patterns of expression of PLD and PLA2-encoding genes were very similar in Navelate and Pinalate leaves, which have similar ABA levels, when comparing both RH conditions. Results comparison with other from previous works in the same experimental systems helped to decipher the effect of the stress severity on the differential response of some of these genes under dehydration conditions and pointed out the interplay between PLA2 and PLD families and their connection with ABA signalling in citrus.

Regulatory function of AMP1 in ABA biosynthesis and drought resistance in arabidopsis

In this study we reported the isolation of a mutant in which the reporter pVP14-LUC was highly expressed in Arabidopsis. The gene expression of maize VP14 is closely correlated with the endogenous ABA levels, and the Arabidopsis homolog of VP14, AtNCED1, encoding an enzyme of ABA biosynthesis, was up-regulated, and high ABA level was detected in the mutant. Map-based cloning revealed that the mutated gene is a novel allele of the AMP1 (Altered Meristem Program 1) which encodes a glutamate carboxypeptidase that plays an important role in shoot apical meristem development and phytohormone homeostasis. We found that the mutant displayed obvious drought tolerance, being with more lateral roots, high seed germination under mannitol, increased ABA accumulation, and highly induced gene expression of RD29A. Using the approaches of artificial microRNA gene silencing in transgenic plants, three AMP1 down-regulated lines were obtained. The AMP1 down-regulated plants exhibited a low rate of water loss, decreased stomatal aperture, and enhanced drought tolerance. These results provide evidence demonstrating the regulatory function of AMP1 in plant drought tolerance and stress responsive gene expression.

Amplification of ABA biosynthesis and signaling through a positive feedback mechanism in seeds

Abscisic acid is an essential hormone for seed dormancy. Our previous study using the plant gene switch system, a chemically induced gene expression system, demonstrated that induction of 9-cis-epoxycarotenoid dioxygenase (NCED), a rate-limiting ABA biosynthesis gene, was sufficient to suppress germination in imbibed Arabidopsis seeds. Here, we report development of an efficient experimental system that causes amplification of NCED expression during seed maturation. The system was created with a Triticum aestivum promoter containing ABA responsive elements (ABREs) and a Sorghum bicolor NCED to cause ABA-stimulated ABA biosynthesis and signaling, through a positive feedback mechanism. The chimeric gene pABRE:NCED enhanced NCED and ABF (ABRE-binding factor) expression in Arabidopsis Columbia-0 seeds, which caused 9- to 73-fold increases in ABA levels. The pABRE:NCED seeds exhibited unusually deep dormancy which lasted for more than 3 months. Interestingly, the amplified ABA pathways also caused enhanced expression of Arabidopsis NCED5, revealing the presence of positive feedback in the native system. These results demonstrated the robustness of positive feedback mechanisms and the significance of NCED expression, or single metabolic change, during seed maturation. The pABRE:NCED system provides an excellent experimental system producing dormant and non-dormant seeds of the same maternal origin, which differ only in zygotic ABA. The pABRE:NCED seeds contain a GFP marker which enables seed sorting between transgenic and null segregants and are ideal for comparative analysis. In addition to its utility in basic research, the system can also be applied to prevention of pre-harvest sprouting during crop production, and therefore contributes to translational biology.

Water relations and growth of original barley plants and its ABA-deficient mutants at increased air temperature

Data on the effects of air temperature increase by 4°C on leaf growth and water relation parameters in barley (Hordeum vulgare L.) plants in original cv. Steptoe and its ABA-deficient mutant (AZ24) are presented. An increase in temperature firstly resulted in the cessation of leaf elongation in both genotypes; however, later in cv. Steptoe plants, as distinct from mutants, the rate of leaf length increment was completely restored. Before air warming, transpiration was more intense in mutant plants; at increased temperature, transpiration was activated in both genotypes. After growth resumption, the water potential in cv. Steptoe plants somewhat increased as compared with initial level (before warming). In AZ34 leaves, in contrast, the water potential, which was initially below that in cv. Steptoe leaves, reduced after temperature increase. The calculation of total hydraulic conductivity of the plants and osmotic hydraulic conductivity in the roots showed that these parameters increased in cv. Steptoe and were not changed in AZ34 mutants. At temperature increase, the level of ABA was not changed in AZ34 mutants, whereas in Steptoe plants it increased in the roots and decreased in the shoots. It was concluded that a capability of ABA synthesis is required for the control of total hydraulic conductivity under changing environmental conditions.

ABA in photoperiodic induction of Pharbitis nil.

The endogenous content of ABA in the cotyledons of <em>Pharbitis nil</em> is high during the light phase before an inductive 16-h-long dark period. During the night, however, at the beginning, the level of ABA is relatively low with the tendency to increase during the second half of an inductive dark period. The dual effect of exogenous ABA on the <em>Pharbitis nil</em> flowering has been observed. ABA applied to the cotyledons on subthreshold photoperiod (12-h-long night) stimulates flower bud formation. On the other hand, however, ABA applied during an inductive (16-h-long) dark period, as well as applied to the medium of cultured plantlets, inhibits flowering. Thus, the flowering effect of ABA is clearly dependent on the state of flower induction which is different in plants growing on various photoperiods.

Growth responses to sulfate and chloride are related to different phytohormone profiles in the halophyte Prosopis strombulifera

In this study, the profile of plant phytohormones traditionally considered as plant growth promoters (GA1, GA3, GA4, IAA and Z) was determined in roots and leaves of the halophyte Prosopis strombulifera grown hydroponically in iso-osmotic solutions of NaCl, Na2SO4 and their mixture. Hormonal levels were correlated with growth parameters and ABA levels. Different sodium salts in the medium differentially affected the synthesis of these compounds. NaCl treated plants showed the greatest accumulation of GA4 and GA1 and lower levels of their metabolites GA8 and GA34 both in root and leaves, in coincidence with the optimum growth observed at ?o -1.9 Mpa this response was also observed at ?o -2.6 MPa. IAA level was unaltered in these plants while Z content was higher in roots than in leaves. In contrast, both leaves and roots from Na2SO4 treated plants showed lower GA1 and GA4 and increased GA8 and GA34 levels at high salinity. High levels of IAA were found in roots of these plants, but the ABA/IAA ratio increased with increasing salt concentrations in the culture medium. This pattern was also observed in the high ABA/GAs ratios. Z levels were very low in all salt treatments. The results of this study show that the halophytic growth under NaCl treatment is mainly regulated by GA1 and GA4 and low relative levels of ABA and IAA. The toxicity of sulfate alters this pattern reversing the ratio ABA/GAs and increasing the synthesis of IAA in conjunction with increased lateral root formation. In bisaline-treated plants intermediate values were observed in the levels of these phytohormones as compared to monosaline treatment.

The effect of nitrogen nutrition on growth and on plant hormones content in Scots pine (Pinus silvestris L.) seedlings grown under light of different intensity

Pine seedlings were cultivated in the Ingested nutrient solution containing N as NH<sub>4</sub>Cl at concentrations of 0 and 500 ppm, under a 16-hr day, at a light intensity of 1500 and 500 lx and temperature ± 20°C. Measurements of seedlings and determination of plant hormones were performed 8 weeks after sowing. It was found that more intensive light stimulated initiation of needles and lateral roots as well as elongation of needles and roots, and increased the fresh weight and dry matter of these organs. Growth stimulation of needles was correlated with an increase in free gibberellins, cytokinins, an ABA-like inhibitor and with a decrease in auxins and water content of tissues. A similar effect of light on plant hormones (except ABA) was also observed in roots. The level of this inhibitor depended on N nutrition. Nitrogen bad a similar effect as light on the growth and initiation of needles and lateral roots. However, it strongly inhibited elongation of roots and increased the water content of the tissues. In needles N increased the level of GAs and auxins, under both light variants, as well as the level of cytokinins, under more intensive light. It decreased the amount of ABA-like inhibitor. In roots the effect of N nutrition on the level of plant hormones depended upon the light intensity. Under light of low intensity N decreased the level of GAs and ABA, increased the level of auxins and had nonsignificant influence on the level of cytokinins. Under more intensive light it had no effect on the GAs and auxin levels and increased the level of cytoikinins and the ABA-like inhibitor.

Impact of Methyl Jasmonate on Antioxidant Activity and Some Biochemical Aspects of Maize Plant Grown under Water Stress Condition

A pot-culture study was undertaken to investigate the possible role of Methyl jasmonate (MeJA)-treatment on the earlier vegetative growth stage and different chemical constituents of maize cultivar (Giza-2) plants subjected to water stress. The grains were divided into two groups: first group was pre-soaked in water, and the second one was pre-soaked in 50 μM MeJA for 8 h. The plants were subjected to different levels of water field capacity (WFC) 65%, 55% and 45%. The results showed that pre-soaking maize grains with MeJA led to increases in plant growth criteria evident in terms of plant height, fresh and dry weight of plant. The pigment levels concomitantly with total carbohydrates, total soluble sugar, polysaccharides, as well as free amino acids, proline and total protein content were markedly increased. Moreover, the application of the investigated MeJA significantly improved growth hormone in terms of IAA. In contrast ABA level was markedly declined in maize plant. The activities of oxidative CAT, POX and SOD were also increased with MeJA. In addition, the N, P and K content was increased significantly in shoot. As a conclusion, soaking maize grains with MeJA could alleviate the harmful effects of water stress.

BHLH122 is important for drought and osmotic stress resistance in Arabidopsis and in the repression of ABA catabolism

• Although proteins in the basic helix-loop-helix (bHLH) family are universal transcription factors in eukaryotes, the biological roles of most bHLH family members are not well understood in plants. • The Arabidopsis thaliana bHLH122 transcripts were strongly induced by drought, NaCl and osmotic stresses, but not by ABA treatment. Promoter::GUS analysis showed that bHLH122 was highly expressed in vascular tissues and guard cells. Compared with wild-type (WT) plants, transgenic plants overexpressing bHLH122 displayed greater resistance to drought, NaCl and osmotic stresses. In contrast, the bhlh122 loss-of-function mutant was more sensitive to NaCl and osmotic stresses than were WT plants. • Microarray analysis indicated that bHLH122 was important for the expression of a number of abiotic stress-responsive genes. In electrophoretic mobility shift assay and chromatin immunoprecipitation assays, bHLH122 could bind directly to the G-box/E-box cis-elements in the CYP707A3 promoter, and repress its expression. Further, up-regulation of bHLH122 substantially increased cellular ABA levels. • These results suggest that bHLH122 functions as a positive regulator of drought, NaCl and osmotic signaling.

Changes in growth, hormones levels and essential oil content of Ammi visnaga L. plants treated with some bioregulators

The effects of foliar application of different concentrations of amino acids (tyrosine and phenylalanine) and phenolic acids (trans-cinnamic acid, benzoic acid and salicylic acid) on growth, pigment content, hormones levels and essential oil content of Ammi visnaga L were carried out during two successive seasons. It is clear that foliar application of either amino acids or phenolics significantly promoted the growth parameters in terms of shoot height, fresh and dry biomass, number of branches and number of umbels per plant. The increment of growth parameter was associated with elevated levels of growth promoters (IAA, GA3, total cytokinins) and low level of ABA. The greatest increase in the previously mentioned parameters was measured in plants exposed to different concentrations of phenols particularly in benzoic acid-treated plants. Such effect was concentration dependent. All treatments led to significant increments in yield seeds and oil content. Moreover, gas liquid chromatographic analysis revealed that the main identified components of essential oil were 2,2-dimethyl butanoic acid, isobutyl isobutyrate, α-isophorone, thymol, fenchyl acetate and linalool. Phenolics and amino acid treatments resulted in qualitative differences in these components of essential oil.

Endogenous abscisic acid signaling towards storage reserve filling in developing seed tissues of castor bean (Ricinus communis L.)

Abscisic acid (ABA; free form) is a naturally occurring physiological growth hormone of higher plants. A detailed study involving the time course growth of developing seed tissues associated with endogenous levels of free ABA were investigated using a novel enzyme-linked immunosorbent assay. Seed filling in castor (Ricinuc communis L.) endosperm, embryo, and pod is marked with a rapid increase in fresh weight during the mid-developmental stages [21–42 days after pollination (DAP)], followed by a steady decline at the maturation stages (42–63 DAP) accompanied with a rapid lipid synthesis (in endosperm and embryo) during the same period, except for in pod. Endogenous ABA levels in endosperm (0.001–0.32 μg/g) and embryo (0.003–0.13 μg/g) followed a concurrent pattern with seed reserve filling, showing a rapid increase during the mid-developmental stages 21–42 DAP, whereas ABA levels in seed pod (0.2–22.9 μg/g) showed a different accumulation pattern with rapid increase and decline during the early-mid developmental stages, preceded by the maximal increase during the maturation stage (63 DAP). Together, our results provide evidence for the association of endogenous ABA in seed filling as well as in reserve deposition and provides clue for the effective usage of exogenous ABA concentrations in developing seeds with a focus, on improving seed reserve complex in castor.

A Transcript Profiling Approach Reveals an Abscisic Acid-Specific Glycosyltransferase (UGT73C14) Induced in Developing Fiber of Ligon lintless-2 Mutant of Cotton (Gossypium hirsutum L.)

Ligon lintless-2, a monogenic dominant cotton (Gossypium hirsutum L.) fiber mutation, causing extreme reduction in lint fiber length with no pleiotropic effects on vegetative growth, represents an excellent model system to study fiber elongation. A UDP-glycosyltransferase that was highly expressed in developing fibers of the mutant Ligon lintless-2 was isolated. The predicted amino acid sequence showed ~53% similarity with Arabidopsis UGT73C sub-family members and the UDP-glycosyltransferase was designated as UGT73C14. When expressed in Escherichia coli as a recombinant protein with a maltose binding protein tag, UGT73C14 displayed enzymatic activity toward ABA and utilized UDP-glucose and UDP-galactose as the sugar donors. The recombinant UGT73C14 converted natural occurring isoform (+)-cis, trans-ABA better than (+)-trans, trans-ABA and (-)-cis, trans-ABA. Transgenic Arabidopsis plants constitutively overexpressing UGT73C14 did not show phenotypic changes under standard growth conditions. However, the increased glycosylation of ABA resulted in phenotypic changes in post-germinative growth and seedling establishment, confirming in vivo activity of UGT73C14 for ABA. This suggests that the expression level of UGT73C14 is regulated by the observed elevated levels of ABA in developing fibers of the Li 2 mutant line and may be involved in the regulation of ABA homeostasis.

Overexpression of Arabidopsis XERICO gene confers enhanced drought and salt stress tolerance in rice (Oryza Sativa L.)

Drought and salinity are two major limiting factors in rice (Oryza. sativa L.) productivity worldwide. XERICO, encoding a RING-H2 zinc finger protein, substantially enhanced drought tolerance by increasing ABA biosynthesis in Arabidopsis. Here, we report the isolation of the full-length cDNA of XERICO from Arabidopsis and its heterologous expression in rice (O. sativa L.). Homozygous transgenic plants overexpressing XERICO (OE-XERICO) exhibited hypersensitivity to stress stimuli (salt, osmotic stress and exogenous ABA) during seed germination and early seedling growth. When subjected to dehydration and salinity stress, 4-week-old transgenic seedlings showed a considerable increase in tolerance to these stimuli compared with that of the wild type (WT) seedlings. Detached leaves from the transgenic rice lines showed lower transpirational water loss than WT. The OE-XERICO lines exhibited a significant increase in endogenous ABA contents, and expression levels of Four ABA biosynthesis or ABA-response genes, OsNCED, OsABA3, OsABI5, OsLEA3-1, under drought and salt stress condition. These results suggest that the overexpression of XERICO in rice plants confers improved drought and salt tolerance probably through enhanced ABA level and ABA-mediated stress response.