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PubMed2003

New fava bean guard cell signaling mutant impaired in ABA-induced stomatal closure.

We isolated a mutant from Vicia faba L. cv. House Ryousai. It wilts easily under strong light and high temperature conditions, suggesting that its stomatal movement may be disturbed. We determined responses of mutant guard cells to some environmental stimuli. Mutant guard cells demonstrated an impaired ability to respond to ABA in 0.1 mM CaCl(2) and stomata did not close in the presence of up to 1 mM ABA, whereas wild-type stomata closed when exposed to 10 micro M ABA. Elevating external Ca(2+) caused a similar degree of stomatal closure in the wild type and the mutant. A high concentration of CO(2) (700 micro l liter(-1)) induced stomatal closure in the wild type, but not in the mutant. On the basis of these results, we propose the working hypothesis that the mutation occurs in the region downstream of CO(2) and ABA sensing and in the region upstream of Ca(2+) elevation. The mutant is named fia (fava bean impaired in ABA-induced stomatal closure).

Abscisic Acid↗
PubMed2005

The AIP2 E3 ligase acts as a novel negative regulator of ABA signaling by promoting ABI3 degradation.

The phytohormone abscisic acid (ABA) mediates many complex aspects of plant development including seed maturation, dormancy, and germination as well as root growth. The B3-domain transcription factor abscisic acid-insensitive 3 (ABI3) is a central regulator in ABA signaling, but little is known of how this factor is regulated. Here, we show that ABI3 is an unstable protein and that an ABI3-interacting protein (AIP2), which contains a RING motif, can polyubiquitinate ABI3 in vitro. The AIP2 E3 ligase activity is abolished by mutations (C230S; C231S) in the RING motif and the AIP2 (C/S) mutant functions in a dominant-negative manner. AIP2 has a stronger binding affinity for the B2 + B3 domain of ABI3 than the A1 + B1 domain, but only ubiquitinates the latter. In double-transgenic plants, induced AIP2 expression leads to a decrease in ABI3 protein levels. In contrast, ABI3 levels are elevated upon induced expression of the AIP2 RING mutant, which interferes with the endogenous AIP2 E3 activity. An aip2-1-null mutant shows higher ABI3 protein levels compared with wild type after seed stratification, and is hypersensitive to ABA, mimicking the ABI3-overexpression phenotype, whereas AIP2-overexpression plants contain lower levels of ABI3 protein than wild type and are more resistant to ABA, phenocopying abi3. Our results indicate that AIP2 negatively regulates ABA signaling by targeting ABI3 for post-translational destruction.

Abscisic Acid↗
PubMed1989

Endogenous ABA in Growing Maize Roots: Light Effects.

The growth of intact maize (Zea mays L.) roots and the abscisic acid (ABA) content (measured by gas chromatography-mass spectrometry of the root tip were analyzed after a white-light treatment. The decrease of the elongation rate due to the illumination corresponded to a concomitant increase in the ABA found in the root. When selecting roots, on the basis of their growth rate, it was possible to show that the relation between growth and ABA content, previously reported in darkness was conserved after light treatments. Therefore, light decreased the root growth rate while it simultaneously increased the ABA content in the roots. This increase was higher than expected, demonstrating the complexity of the involvement of ABA on root growth.

Journal Article↗
PubMed1993

The ABA-1 allergen of the nematode Ascaris suum: epitope stability, mass spectrometry, and N-terminal sequence comparison with its homologue in Toxocara canis.

ABA-1 is a major allergen of nematode parasites of the genus Ascaris which includes the large roundworms of humans and pigs, A. lumbricoides and A. suum, respectively. The allergen was purified from A. suum by immunoaffinity chromatography for immunochemical examination. The IgE antibody repertoire is under MHC control in infected rodents and the IgE-binding epitopes were robust to treatment with heat or periodate, and electroblotting on nitrocellulose. This implies that the IgE epitopes comprise primary peptide sequence or an unusually stable secondary or tertiary structure. The molecular mass of ABA-1 is controversial, but mass spectrometry analysis indicated that there were five components of similar size, with the major species being 14,643.2 +/- 1.4 D. Finally, N-terminal sequence analysis of ABA-1 and TBA-1 (the homologue in the canine nematode infective to humans, Toxocara canis) revealed a high degree of similarity, and we have previous evidence that ABA-1 homologues are widespread amongst ascaridid parasites of humans. ABA-1 and its homologues might, therefore, be important to the immunopathology of many infections with nematode parasites, upon which the genetic constitution of the hosts will also have a bearing.

Allergens↗
PubMed2004

Beta-amino-butyric acid-induced resistance against necrotrophic pathogens is based on ABA-dependent priming for callose.

The non-protein amino acid beta-amino-butyric acid (BABA) protects plants against a wide range of pathogens. We have examined the effectiveness and mode of action of BABA on resistance against two necrotrophic pathogens. Treatment of Arabidopsis with BABA induced resistance against Alternaria brassicicola and Plectosphaerella cucumerina to a similar level by jasmonic acid (JA). Conversely, treatment with benzothiadiazole (BTH), a functional analogue of salicylic acid (SA), had no significant effect on the resistance against both pathogens. BABA-induced resistance against A. brassicicola and P. cucumerina was unaffected in the JA-insensitive mutant coi1-1 and the camalexin-deficient mutant pad3-1. Moreover, the expression of BABA-induced resistance was not associated with enhanced accumulation of camalexin or enhanced transcription of the JA-inducible PDF1.2 gene. The expression of BABA-induced resistance against P. cucumerina was unaffected in mutants impaired in ethylene (ET) and SA signalling, but was blocked in the abscisic acid (ABA)-deficient mutant aba1-5, the ABA-insensitive mutant abi4-1 and the callose-deficient mutant pmr4-1. Upon infection by both pathogens, BABA-treated plants showed an earlier and more pronounced accumulation of callose. Treatment with the callose-inhibitor 2-deoxy-D-glucose (2-DDG) reversed the BABA-induced resistance against A. brassicicola. Furthermore, primed callose deposition was absent in BABA-treated abi4-1 and pmr4-1 plants upon infection by P. cucumerina. Although the expression of BABA-induced resistance was not associated with enhanced transcription of the ABA-inducible RAB18 gene, application of ABA mimicked the effect of BABA on the level of callose accumulation and resistance. Hence, BABA-induced resistance against necrotrophic pathogens is based on primed callose accumulation, which is controlled by an ABA-dependent defence pathway.

Abscisic Acid↗
PubMed2005

Sugar and ABA responsiveness of a minimal RBCS light-responsive unit is mediated by direct binding of ABI4.

Photosynthesis-associated nuclear genes (PhANGs) are able to respond to multiple environmental and developmental signals, including light, sugars and abscisic acid (ABA). PhANGs have been extensively studied at the level of transcriptional regulation and several cis-acting elements important for light responsiveness have been identified in their promoter sequences. However, the regulatory elements involved in sugar and ABA regulation of PhANGs have not been completely characterized. Using conserved modular arrangement 5 (CMA5), a previously characterized minimal light-responsive unit, we show that in Arabidopsis thaliana this unit responds not only positively to light signals, but also negatively to sugars and ABA. The latter responses were found to be impaired in the abi4 mutant, indicating that ABSCISIC ACID INSENSITIVE-4 (ABI4) is a regulator involved in sugar and ABA repression of this minimal regulatory unit. Furthermore, we report a new sequence element conserved in several rbcS promoters, herewith named S-box, which is important for the sugar and ABA responsiveness of CMA5. This sequence corresponds to a putative ABI4-binding site, which is in fact bound by the Arabidopsis ABI4 protein in vitro. The S-box is closely associated with the G-box present in CMA5, and this association is conserved in the promoters of several RBCS genes. This phylogenetically conserved promoter feature probably reflects a common regulatory mechanism and identifies a point of convergence between light- and sugar-signaling pathways.

Abscisic Acid↗
PubMed2026

Positive feedback loop between RAF12 and ABI5 reinforces ABA-mediated suppression of Arabidopsis seed germination.

ABA-INSENSITIVE 5 (ABI5) is a key transcriptional regulator mediating abscisic acid (ABA)-induced suppression of seed germination. However, the downstream regulatory network through which ABI5 exerts its function remains incompletely understood. Here, by integrating ChIP-seq and RNA-seq analyses, we identify RAF12, a member of the B2 Raf-like kinase subfamily, as a direct transcriptional target of ABI5. ABI5 binds to the RAF12 promoter and activates its expression. Loss-of-function raf12 mutants exhibit reduced sensitivity to ABA during seed germination, suggesting a negative regulatory role for RAF12 in this process. Conversely, RAF12 interacts with and phosphorylates ABI5, thereby enhancing its transcriptional activity. Further analysis showed that RAF12 regulates its own kinase activity through autophosphorylation. Mutations at its phosphorylation sites significantly weaken its ability to enhance ABI5's transcriptional activity. Together, these findings uncover a positive feedback loop wherein ABI5 transcriptionally activates RAF12, which in turn reinforces ABI5 activity through phosphorylation. This module may function in parallel with the canonical SnRK2s-ABI5-mediated ABA signaling cascade, offering new mechanistic insights into the fine-tuning of ABA responses during seed germination.

Arabidopsis↗
PubMed1983

Hapten-specific help mediated by an anti-ABA T cell line.

Long-term cultures of functional T cells were grown from mice injected with azobenzene arsonate (ABA) coupled spleen cells or mice painted with the diazonium salt of p-phenylarsonate. All cell lines produced delayed hypersensitivity to ABA. When tested for helper function in an antibody-forming cell assay only one line, AA3, helped plaque-forming cell formation. It was able to help anti-FLU response of FLU-HGG primed B cells to ABA-KLH-FLU. The help required linkage of the ABA and FLU determinants because cultures stimulated with a mixture of ABA-KLH and TNP-KLH-FLU did not show increased PFC. These experiments demonstrate hapten-specific help in a system which eliminates involvement of passively absorbed antibody in hapten recognition.

Animals↗
PubMed2002

ABA, ethylene and the control of shoot and root growth under water stress.

The question of whether abscisic acid (ABA) acts as an inhibitor or promoter of shoot growth in plants growing in drying soil is examined, drawing on current understanding of the role of ABA in root growth maintenance. Particular consideration is given to studies of endogenous ABA deficiency, which have shown that an important role of ABA is to limit ethylene production, and that this interaction is involved in the effects of ABA status on shoot and root growth.

Abscisic Acid↗
PubMed2002

Stomatal control in tomato with ABA-deficient roots: response of grafted plants to soil drying.

The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA-deficient tomato mutants, sitiens and flacca and their near-isogenic wild-type parent. Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens or flacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA. In the second type of experiment, wild-type shoots were grafted onto a split-root system consisting of one wild-type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild-type roots. In the third type of experiment, grafted plants with wild-type shoots and either wild-type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens. These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.

Abscisic Acid↗
PubMed2001

[Studies on ABA-induced H2O2 in Vicia guard cells by means of confocal laser scanning microscopy].

The methods of confocal laser scanning microscopy (CLSM) and microinjection were used to study ABA-induced H2O2 in guard cells (Vicia faba), which were labeled with H2O2 specific probe-2, 7-dichlorofluorescin diacetate(H2DCFDA). The results indicated 100 U/mL catalase (CAT) could inhibit partly stomatal closure induced by ABA. 10(-3) mmol/L ABA could significantly induce H2O2 production in chloroplast in guard cells of Vicia faba following microinjection, and 100 U/mL CAT could partly abolish the effects following simultaneous microinjection of ABA and CAT. These suggest that H2O2 is possibly involved in ABA signaling leading to stomatal closure.

Abscisic Acid↗
PubMed1981

Allorestriction and xenorestriction phenomena in the induction of delayed-type hypersensitivity (DTH) responses in the guinea pig against azobenzenearsonate- (ABA) modified peritoneal exudate cells.

The role of MHC products in the induction of DTH responses Ia antigens play a crucial role in these cells in the recognition of ABA determinants by lymphocytes. Second, JY-1 guinea pigs were employed as responder animals. A clear allorestriction phenomenon was observed again when weakly modified ABA-PEC were used. On the other hand, the allorestriction phenomenon was apparently abrogated when heavily modified ABA-PEC were employed: allogeneic as well as syngeneic ABA-PEC induced strong and comparable DTH responses. Even in this condition, xenogeneic (mouse) ABA-PEC were barely immunogeneic, On the basis of these observations, the cross-reactivity of Ia antigens in the conjunctive recognition of haptenic determinants by T cells is discussed.

Animals↗
PubMed1998

Inhibition of germination gene expression by Viviparous-1 and ABA during maize kernel development.

Two maize glyoxysomal genes expressed during germination, malate synthase (MS) and isocitrate lyase (ICL), were used to characterize the regulatory roles of the Viviparous-1 (Vp1) regulatory gene and abscisic aicd (ABA) in the induction of embryo quiescence during kernel development. In wild-type maize embryo, MS and ICL transcripts were first detected at 2 (MS) or 3 (ICL) days after germination (DAG), peaked at 5 DAG, and decreased thereafter. By reverse transcriptase-polymerase chain reaction (RT-PCR), the germination-specific genes were amplified in both ABA-insensitive (vp1) and ABA-deficient (vp7 and vp10) mutant embryos at 26 and 33 days after pollination (DAP), but not in wild-type embryos. The repression of these germination-specific genes thus requires the Vp1 gene product and normal levels of ABA to induce embryo quiescence during kernel development. This suggests that a genetic regulatory system exists to prevent vivipary in developing maize embryos. The involvement of the Vp1 gene product and ABA in repressing germination-specific genes complements their previously defined roles in the induction of seed-specific genes such as C1.

Abscisic Acid↗
PubMed1993

The cis-regulatory element CCACGTGG is involved in ABA and water-stress responses of the maize gene rab28.

The maize gene rab28 has been identified as ABA-inducible in embryos and vegetative tissues. It is also induced by water stress in young leaves. The proximal promoter region contains the conserved cis-acting element CCACGTGG (ABRE) reported for ABA induction in other plant genes. Transient expression assays in rice protoplasts indicate that a 134 bp fragment (-194 to -60 containing the ABRE) fused to a truncated cauliflower mosaic virus promoter (35S) is sufficient to confer ABA-responsiveness upon the GUS reporter gene. Gel retardation experiments indicate that nuclear proteins from tissues in which the rab28 gene is expressed can interact specifically with this 134 bp DNA fragment. Nuclear protein extracts from embryo and water-stressed leaves generate specific complexes of different electrophoretic mobility which are stable in the presence of detergent and high salt. However, by DMS footprinting the same guanine-specific contacts with the ABRE in both the embryo and leaf binding activities were detected. These results indicate that the rab28 promoter sequence CCACGTGG is a functional ABA-responsive element, and suggest that distinct regulatory factors with apparent similar affinity for the ABRE sequence may be involved in the hormone action during embryo development and in vegetative tissues subjected to osmotic stress.

Abscisic Acid↗
PubMed1992

Developmental and organ-specific expression of an ABA- and stress-induced protein in barley.

An mRNA species, HVA1, has been shown to be rapidly induced by abscisic acid (ABA) in barley aleurone layers (Hong, Uknes and Ho, Plant Mol Biol 11: 495-506, 1988). In the current work we have investigated the expression of HVA1 in other organs of barley plants. In developing seeds, HVA1 mRNA is not detected in starchy endosperm cells, yet it accumulates in aleurone layers and embryo starting 25 days after anthesis, and its level remains high in these organs in dry seeds. Although the levels of HVA1 mRNA are equivalent in the dry embryos of dormant and nondormant barley seeds, upon imbibition HVA1 mRNA declines much slower in the dormant than in the nondormant embryos. The HVA1 mRNA and protein levels are highly induced by ABA treatment in all organs of 3-day-old seedlings. However, the induction in the leaf of 7-day-old seedlings is less than one tenth the level observed in the leaf of 3-day-old seedlings. In the leaf, HVA1 mRNA and protein are induced mainly at the base. These observations indicate that the expression of HVA1 is under developmental regulation. Besides the HVA1 protein, a smaller protein (p20) of approximately 20 kDa cross-reacting with anti-HVA1 polyclonal antibodies, is induced by ABA in barley seedlings but not in seeds. HVA1 mRNA is induced by drought, NaCl, cold or heat treatment. Similar to ABA treatment, the drought induction of HVA1 occurs in all the tissues of 3-day-old seedlings, but the induction decreases dramatically in the leaf of 7-day-old plants. The significance of organ-specific, developmentally regulated, and stress-induced expression of HVA1 is discussed.

Abscisic Acid↗
PubMed1995

Promoters from kin1 and cor6.6, two homologous Arabidopsis thaliana genes: transcriptional regulation and gene expression induced by low temperature, ABA, osmoticum and dehydration.

The Arabidopsis thaliana genes kin1 and cor6.6 belong to the same family and were expressed at higher levels following low temperature and ABA treatments. In an attempt to elucidate the mechanism of gene regulation by low temperature, the relationship between low-temperature- and abscisic acid (ABA)-induced gene expression and possible differential expression of the two genes, we have cloned a 5.3 kb genomic fragment harboring kin1 and cor6.6 and their respective 5' sequences. The putative promoters of both genes were fused to the beta-glucuronidase (GUS) coding sequence and GUS expression was analysed in transgenic tobacco and Arabidopsis plants. The cor6.6 promoter produced a higher basal level of expression than the kin1 promoter in transgenic tobacco. Enzyme assays of inducible GUS activity in transgenic Arabidopsis and tobacco plants showed that GUS activity directed by both kin1 and cor6.6 promoters was significantly induced by ABA, dehydration and osmoticum, but not by low temperature. Northern analysis revealed, in contrast, that GUS mRNA was significantly induced in these transgenic plants by low temperature. Further analysis showed that, at low temperature, GUS protein synthesis from the induced GUS mRNA was inhibited. Together these results reveal induction of kin1 and cor6.6 transcription by low temperature, exogenous ABA and dehydration. However, low-temperature expression is dramatically reduced at the translational level.

Abscisic Acid↗
PubMed2004

Abscisic acid-inducible nuclear proteins bind to bipartite promoter elements required for ABA response and embryo-regulated expression of the carrot Dc3 gene.

The carrot (Daucus carota L.) lea-class gene Dc3 is expressed in developing seeds and in vegetative tissues subject to drought and treatment with exogenous abscisic acid (ABA). Cis regulatory elements involved in seed-specific expression and in response to ABA were identified in transgenic tobacco (Nicotiana tabacum L.) using beta-glucuronidase (GUS) reporter gene constructs containing a series of deletion and orientation mutants of the Dc3 promoter. These experiments demonstrated that the Dc3 promoter is comprised of a proximal promoter region (PPR) and a distal promoter region (DPR). TCGTGT motifs in the DPR in combination with the PPR comprise a novel, bipartite ABA module in the Dc3 gene promoter. The PPR contains cis-acting elements responsible for the developmental regulation of Dc3 expression in seeds. Five similar sequence motifs with the consensus ACACgtGCa were identified in the PPR. Both DPR and PPR interact with common nuclear proteins that are present in embryos and are inducible by ABA in vegetative tissues.

Abscisic Acid↗
PubMed2005

Expression of PsGRP1, a novel glycine rich protein gene of Pisum sativum, is induced in developing fruit and seed and by ABA in pistil and root.

A novel glycine-rich protein gene, PsGRP1, has been identified in Pisum sativum L. Accumulation of PsGRP1 transcripts was observed in reproductive organs and vegetative tissues. They were localized in endocarp sclerenchyma during fruit development in cells that will lignify. PsGRP1 expression was also detected in senescent pistils and developing seeds and induced by ABA treatment in presenescent pistils. A raise in the expression was also observed in roots after treatment with ABA or mannitol but not under cold stress. A mannitol treatment induced a rise in ABA levels and fluridone treatment counteracted the mannitol induction of PsGRP1 expression. The results suggest a possible role for PsGRP1 in differentiation of the endocarp sclerenchyma and during seed development, pistil senescence and osmotic stress under ABA control.

Abscisic Acid↗