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PubMed2006

ABA-responsive RNA-binding proteins are involved in chloroplast and stromule function in Arabidopsis seedlings.

The phytohormone abscisic acid (ABA) regulates essential growth and developmental processes in plants. Recently, RNA-binding proteins have been described as components of ABA signaling during germination. We have identified ten ABA-regulated RNA-binding proteins in Arabidopsis seedlings. Among those genes, AtCSP41B and cpRNP29 are highly expressed in seedlings. Using promoter:reporter gene analyses, we showed that both AtCSP41B and cpRNP29 were in particular expressed in photosynthetically active organs like green cotyledons, leaves, and petioles. The analysis of CFP-fusion proteins demonstrates that cpRNP29 localized to chloroplasts and AtCSP41B to chloroplasts and stromules. Whereas RNA-binding of cpRNP29 has previously been shown, we demonstrated through in vitro RNA-binding assays that recombinant AtCSP41B binds to RNA, and that chloroplast petD RNA can serve as a target of AtCSP41B. Developmental or environmental stimuli affected the expression of AtCSP41B and cpRNP29 in seedlings. Both genes were repressed during senescence, but only AtCSP41B was significantly repressed upon water stress. In addition, AtCSP41B and cpRNP29 exhibited low expression in etiolated seedlings compared to green seedlings, and cpRNP29 was regulated during the day photoperiod. Homozygous T-DNA insertion lines were isolated, characterized on the molecular level, and monitored for phenotypic changes. Taken together, the data show that both proteins are regulated during processes that are known to involve ABA signaling. Their localization in chloroplasts and RNA-binding activity suggest a role in chloroplast RNA metabolism in Arabidopsis seedlings.

Abscisic Acid↗
PubMed2005

Regulation of genes associated with auxin, ethylene and ABA pathways by 2,4-dichlorophenoxyacetic acid in Arabidopsis.

The chemical 2,4-dichlorophenoxyacetic acid (2,4-D) regulates plant growth and development and mimics auxins in exhibiting a biphasic mode of action. Although gene regulation in response to the natural auxin indole acetic acid (IAA) has been examined, the molecular mode of action of 2,4-D is poorly understood. Data from biochemical studies, (Grossmann (2000) Mode of action of auxin herbicides: a new ending to a long, drawn out story. Trends Plant Sci 5:506-508) proposed that at high concentrations, auxins and auxinic herbicides induced the plant hormones ethylene and abscisic acid (ABA), leading to inhibited plant growth and senescence. Further, in a recent gene expression study (Raghavan et al. (2005) Effect of herbicidal application of 2,4-dichlorophenoxyacetic acid in Arabidopsis. Funct Integr Genomics 5:4-17), we have confirmed that at high concentrations, 2,4-D induced the expression of the gene NCED1, which encodes 9-cis-epoxycarotenoid dioxygenase, a key regulatory enzyme of ABA biosynthesis. To understand the concentration-dependent mode of action of 2,4-D, we further examined the regulation of whole genome of Arabidopsis in response to a range of 2,4-D concentrations from 0.001 to 1.0 mM, using the ATH1-121501 Arabidopsis whole genome microarray developed by Affymetrix. Results of this study indicated that 2,4-D induced the expression of auxin-response genes (IAA1, IAA13, IAA19) at both auxinic and herbicidal levels of application, whereas the TIR1 and ASK1 genes, which are associated with ubiquitin-mediated auxin signalling, were down-regulated in response to low concentrations of 2,4-D application. It was also observed that in response to low concentrations of 2,4-D, ethylene biosynthesis was induced, as suggested by the up-regulation of genes encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase. Although genes involved in ethylene biosynthesis were not regulated in response to 0.1 and 1.0 mM 2,4-D, ethylene signalling was induced as indicated by the down-regulation of CTR1 and ERS, both of which play a key role in the ethylene signalling pathway. In response to 1.0 mM 2,4-D, both ABA biosynthesis and signalling were induced, in contrast to the response to lower concentrations of 2,4-D where ABA biosynthesis was suppressed. We present a comprehensive model indicating a molecular mode of action for 2,4-D in Arabidopsis and the effects of this growth regulator on the auxin, ethylene and abscisic acid pathways.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2006

Evidence that Agaricus bisporus agglutinin (ABA) has dual sugar-binding specificity.

Agaricus bisporus agglutinin (ABA) is known as a useful lectin to detect T-antigen (Core1) disaccharide (Galbeta1-3GalNAcalpha) and related O-linked glycans. However, a recent X-ray crystallographic study revealed the presence of another intrinsic sugar-binding site, i.e., for GlcNAc. To confirm this possibility, detailed analysis was performed using two advanced methods: lectin microarray and frontal affinity chromatography (FAC). In the lectin microarray, intense signals were observed on ABA spots for both N-glycanase-treated and O-glycanase/beta1-4galactosidase-treated Cy3-labeled asialofetuin. This indicates substantial affinity for both O-linked and agalactosylated (GlcNAc-exposed) N-linked glycans. A further approach by FAC using 20 pNP and 130 PA-oligosaccharides demonstrated that ABA bound to Core1 (K(d) = 3.4 x 10(-6) M) and Core2 (1.9 x 10(-5) M) but not to Core3 and Core6 O-linked glycans. It also showed substantial affinity to mono-, bi-, and tri-antennary agalactosylated complex-type N-linked glycans (K(d) > 1.8 x 10(-5) M). These results establish ABA as a lectin having dual sugar-binding sites with distinct specificity, i.e., for Gal-exposed O-linked glycans and GlcNAc-exposed N-linked glycans.

Agglutinins↗
PubMed2006

Genome wide cDNA-AFLP analysis of genes rapidly induced by combined sucrose and ABA treatment in rice cultured cells.

We identified 27 genes induced by combined sucrose and ABA treatment from rice cultured cells with cDNA-AFLP. Thirteen of these up-regulated genes were induced 30 min after the co-treatment. This suite of genes includes starch biosynthesis related genes. Type A genes were expressed only in the presence of both sucrose and ABA. Type B genes were expressed in the presence of sucrose or ABA and the expression was dramatically enhanced by the co-treatment of sucrose and ABA. These results indicate that multiple steps of starch biosynthesis and other processes may be regulated by at least two different pathways.

Abscisic Acid↗
PubMed2001

Morphological characterization of microspheres, films and implants prepared from poly(lactide-co-glycolide) and ABA triblock copolymers: is the erosion controlled by degradation, swelling or diffusion?

Erosion of biodegradable parenteral delivery systems (PDS) based on ABA copolymers consisting of poly(L-lactide-co-glycolide) (PLGA) A-blocks attached to polyethylene oxide (PEO) B-blocks, or PLGA is important for the release of macromolecular drugs. The degradation behavior of four types of PDS, namely extruded rods, tablets, films and microspheres, was studied with respect to molecular weight, mass, polymer composition and shape and microstructure of the PDS. For each device the onset time of bulk erosion (t(on)) and the apparent rate of mass loss (k(app)) were calculated. In the case of PLGA, the t(on) was 16.2 days for microspheres, 19.2 days for films and 30.1 days for cylindrical implants and tablets. The k(app) was 0.04 days(-1) for microspheres, 0.09 days(-1) for films, 0.11 days(-1) for implants and 0.10 days(-1) for tablets. The degradation rates were in the same range irrespective of the geometry and the micrographs of eroding PDS demonstrated pore formation; therefore, a complex pore diffusion mechanism seems to control the erosion of PLGA devices. In contrast, PDS based on ABA copolymers showed swelling, followed by a parallel process of molecular weight degradation and polymer erosion, independent of the geometry. The contact angles of ABA films increased either with decreasing PEO content or with increasing chain length of the PEO B-blocks. In summary, the insertion of a hydrophilic B-block leads to an erosion controlled by degradation of ABA copolymers, whereas for PLGA a complex pore diffusion of degradation products controls the rate of bulk erosion.

Biodegradation, Environmental↗
PubMed1997

Tissue-specific activation of the osmotin gene by ABA, C2H4 and NaCl involves the same promoter region.

The gene encoding the antifungal protein osmotin is induced by several hormonal and environmental signals. In this study, tissue-specific and inducer-mediated expression of the reporter gene beta-glucuronidase (uidA) fused to different fragment lengths of the osmotin promoter was evaluated in transgenic tobacco (Nicotiana tabacum). The region of the promoter between -248 to -108 (Fragment A) was found to be essential and sufficient for inducer (abscisic acid (ABA), C2H4 and NaCl)-mediated expression of the reporter gene. Expression of the reporter gene was developmentally regulated and increased with maturity of leaves, stem and flowers. Expression also was tissue-specific being most highly expressed in epidermis and vascular parenchyma of the stem. The regulators ABA, C2H4 and NaCl exhibited tissue-specific induction of this promoter. The promoter was specifically responsive to C2H4 in flowers at virtually all stages of development, but not responsive in these tissues to ABA or NaCl. Conversely, ABA and NaCl were able to induce reporter gene activity using promoter Fragment A in specific tissues of root where C2H4 was unable to induce activity. Further dissection of the promoter Fragment A into fragments containing either the conserved GCC element (PR); PR/AT; or G/AT sequences, and subsequent testing of these fragments fused to GUS in transgenic plants was performed. These experiments revealed that the promoter fragment containing PR element alone, although required, was barely able to allow responsiveness to C2H4. However, significant C2H4-induced activity was obtained with a promoter fragment containing the AT and PR elements together.

Abscisic Acid↗
PubMed1998

Monitoring microviscosity and microacidity of the albumin microenvironment inside degrading microparticles from poly(lactide-co-glycolide) (PLG) or ABA-triblock polymers containing hydrophobic poly(lactide-co-glycolide) A blocks and hydrophilic poly(ethyleneoxide) B blocks.

PURPOSE: The purpose of this study was to monitor the microenvironment of an encapsulated model protein during the release from biodegradable microparticles (MP) made from three different polymers, namely poly(lactide-co-glycolide) (PLG) and ABA-triblock polymers containing hydrophobic poly(lactide-co-glycolide) A blocks and hydrophilic poly(ethyleneoxide) B blocks with an A:B ratio of 90:10 (ABA1O) and 70:30 (ABA30). METHODS: MP loaded with spin labeled albumin were prepared by a w/o/w technique. The particles were characterized by light scattering and electron microscopy. In vitro release of albumin was determined by size exclusion chromatography. Light microscopic experiments were conducted to visualize water penetration in the matrix. The protein microenvironment inside the degrading microparticles was characterized noninvasively by 2 GHz EPR spectroscopy. RESULTS: Water penetrated rapidly into all MP in the range of few minutes. A burst release was observed for PLG. The release from ABA block-polymers continued for over 14 days despite the rapid solubilization of the protein inside the microparticles. The initial microviscosity of the protein environment inside the ABA particles after exposure to buffer was 2 mm2/s and increased with time. A gradual decrease of the pH to a value of 3.5 was observed within the MP. CONCLUSIONS: The data indicate that the microviscosity and microacidity inside protein loaded microparticles can be studied nondestructively by EPR spectroscopy. Our results clearly demonstrate that ABA-block polymers are superior to PLG allowing a controlled release of proteins from swollen microspheres.

Albumins↗
PubMed2002

AtHVA22 gene family in Arabidopsis: phylogenetic relationship, ABA and stress regulation, and tissue-specific expression.

HVA22 is an ABA- and stress-inducible gene first isolated from barley (Hordeum vulgare L.). Homologues of HVA22 have been found in plants, animals, fungi and protozoa, but not in prokaryotes, suggesting that HVA22 plays a unique role in eukaryotes. Five HVA22 homologues, designated AtHVA22a, b, c, d and e, have been identified in Arabidopsis. These five AtHVA22 homologues can be separated into two subfamilies, with AtHVA22a, b and c grouped in one subfamily and AtHVA22d and e in the other. Phylogenetic analyses show that AtHVA22d and e are closer to barley HVA22 than to AtHVA22a, b and c, suggesting that the two subfamilies had diverged before the divergence of monocots and dicots. The distribution and size of exons of AtHVA22 homologues and barley HVA22 are similar, suggesting that these genes are descendents of a common ancestor. AtHVA22 homologues are differentially regulated by ABA, cold, dehydration and salt stresses. These four treatments enhance AtHVA22a, d and e expression, but have little or even suppressive effect on AtHVA22c expression. ABA and salt stress induce AtHVA22b expression, but cold stress suppresses ABA induction of this gene. Expression of AtHVA22d is the most tightly regulated by these four treatments among the five homologues. In general, AtHVA22 homologues are expressed at a higher level in flower buds and inflorescence stems than in rosette and cauline leaves. The expression level of these homologues in immature siliques is the lowest among all tissues analyzed. It is suggested that some of these AtHVA22 family members may play a role in stress tolerance, and others are involved in plant reproductive development.

Abscisic Acid↗
PubMed1997

The quiescent/colorless alleles of viviparous1 show that the conserved B3 domain of VP1 is not essential for ABA-regulated gene expression in the seed.

A series of vp1 alleles distinguish at least two classes of maturation-related genes that are regulated by the VP1 factor and abscisic acid (ABA). The intermediate vp1-c821708 and vp1-McW alleles have quiescent (non-viviparous) anthocyanin-deficient phenotypes while maintaining significant levels of maturation-specific gene expression in the developing embryo. However, expression of the C1 regulatory gene of the anthocyanin pathway is not detected in these mutants. Reduced steady-state levels of structurally altered VP1 proteins are detected in quiescent mutant embryos. The VP1-McW protein sequence lacks the highly conserved region encoded by exons 3-5 of the Vp1 gene. A sensitive RT-PCR assay was used to rule out significant amounts of intact transcripts in the vp1-McW mutant that could account for the quiescent phenotype. In transient expression assays, the VP1-McW protein and other mutants with a truncated B3 domain of VP1 retained a strong capacity to synergistically enhance ABA-regulation of the Em-GUS reporter gene; whereas transactivation of both Em-GUS and C1-sh-GUS genes in the absence of hormone was strongly inhibited. These results indicate that the largest conserved region in VP1 homologs (B3) is critical for gene activation at low or insignificant ABA dosages; whereas the N-terminal domain provides a key interface with ABA signaling pathways in the developing seed.

Abscisic Acid↗
PubMed2000

Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact Vicia faba leaves during stomatal closure evoked by ABA and darkness.

Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 microM (Ca2+) and 89 microM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.

Abscisic Acid↗
PubMed2003

Interaction between two cis-acting elements, ABRE and DRE, in ABA-dependent expression of Arabidopsis rd29A gene in response to dehydration and high-salinity stresses.

Many abiotic stress-inducible genes contain two cis-acting elements, namely a dehydration-responsive element (DRE; TACCGACAT) and an ABA-responsive element (ABRE; ACGTGG/TC), in their promoter regions. We precisely analyzed the 120 bp promoter region (-174 to -55) of the Arabidopsis rd29A gene whose expression is induced by dehydration, high-salinity, low-temperature, and abscisic acid (ABA) treatments and whose 120 bp promoter region contains the DRE, DRE/CRT-core motif (A/GCCGAC), and ABRE sequences. Deletion and base substitution analyses of this region showed that the DRE-core motif functions as DRE and that the DRE/DRE-core motif could be a coupling element of ABRE. Gel mobility shift assays revealed that DRE-binding proteins (DREB1s/CBFs and DREB2s) bind to both DRE and the DRE-core motif and that ABRE-binding proteins (AREBs/ABFs) bind to ABRE in the 120 bp promoter region. In addition, transactivation experiments using Arabidopsis leaf protoplasts showed that DREBs and AREBs cumulatively transactivate the expression of a GUS reporter gene fused to the 120 bp promoter region of rd29A. These results indicate that DRE and ABRE are interdependent in the ABA-responsive expression of the rd29A gene in response to ABA in Arabidopsis.

Abscisic Acid↗
PubMed2002

Effect of grain colour gene (R) on grain dormancy and sensitivity of the embryo to abscisic acid (ABA) in wheat.

The level of grain dormancy and sensitivity to ABA of the embryo, a key factor in grain dormancy, were examined in developing grains of a white-grained wheat line, Novosibirskaya 67 (NS-67), and its red-grained near-isogenic lines (ANK-1A to -1D); a red-grained line, AUS 1490, and its white-grained mutant line (EMS-AUS). ANK lines showed higher levels of grain dormancy than NS-67 at harvest maturity. AUS 1490 grain also showed higher dormancy than EMS-AUS grain. These results suggest that the R gene for grain colour can enhance grain dormancy. However, the dormancy effect conferred by the R gene was not large, suggesting that it plays a minor role in the development of grain dormancy. Water extracts of AUS 1490 and EMS-AUS bran contained germination inhibitors equivalent to 1-10 microM ABA, although there was no difference in the amount of inhibitors between AUS 1490 and EMS-AUS. Thus, the grain colour gene of AUS 1490 did not appear to enhance the level of grain dormancy by accumulating germination inhibitors in its bran. Sensitivity to ABA of embryos was higher in grains collected around harvest-maturity for ANK lines and AUS 1490, compared with NS-67 and EMS-AUS. The R gene might enhance grain dormancy by increasing the sensitivity of embryos to ABA.

Abscisic Acid↗
PubMed2003

Characterization of Pinalate, a novel Citrus sinensis mutant with a fruit-specific alteration that results in yellow pigmentation and decreased ABA content.

The characterization of a novel mutant, named Pinalate, derived from the orange (Citrus sinensis L. Osbeck) Navelate, which produces distinctive yellow fruits instead of the typical bright orange colouration, is reported. The carotenoid content and composition, and ABA content in leaf and flavedo tissue (coloured part of the skin) of fruits at different developmental and maturation stages were analysed. No important differences in leaf carotenoid pattern of both phenotypes were found. However, an unusual accumulation of linear carotenes (phytoene, phytofluene and zeta- carotene) was detected in the flavedo of Pinalate. As fruit maturation progressed, the flavedo of mutant fruit accumulated high amounts of these carotenes and the proportion of cyclic and oxygenated carotenoids was substantially lower than in the parental line. Full-coloured fruit of Pinalate contained about 44% phytoene, 21% phytofluene, 25% zeta-carotene, and 10% of xanthophylls, whereas, in Navelate, 98% of total carotenoids were xanthophylls and apocarotenoids. The ABA content in the flavedo of Pinalate mature fruit was 3-6 times lower than in the corresponding tissue of Navelate, while no differences were found in leaves. Other maturation processes were not affected in Pinalate fruit. Taken together, the results indicate that Pinalate is a fruit-specific alteration defective in zeta-carotene desaturase or in zeta-carotene desaturase-associated factors. Possible mechanisms responsible for the Pinalate phenotype are discussed. Because of the abnormal fruit-specific carotenoid complement and ABA deficiency, Pinalate may constitute an excellent system for the study of carotenogenesis in Citrus and the involvement of ABA in fruit maturation and stress responses.

Abscisic Acid↗
PubMed2003

ABA, hydrogen peroxide and nitric oxide signalling in stomatal guard cells.

Increased synthesis and redistribution of the phytohormone abscisic acid (ABA) in response to water deficit stress initiates an intricate network of signalling pathways in guard cells leading to stomatal closure. Despite the large number of ABA signalling intermediates that are known in guard cells, new discoveries are still being made. Recently, the reactive oxygen species hydrogen peroxide (H2O2) and the reactive nitrogen species nitric oxide (NO) have been identified as key molecules regulating ABA-induced stomatal closure in various species. As with many other physiological responses in which H2O2 and NO are involved, stomatal closure in response to ABA also appears to require the tandem synthesis and action of both these signalling molecules. Recent pharmacological and genetic data have identified NADPH oxidase as a source of H2O2, whilst nitrate reductase has been identified as a source of NO in Arabidopsis guard cells. Some signalling components positioned downstream of H2O2 and NO are calcium, protein kinases and cyclic GMP. However, the exact interaction between the various signalling components in response to H2O2 and NO in guard cells remains to be established.

Abscisic Acid↗
PubMed2002

The possible involvement of a phosphate-induced transcription factor encoded by phi-2 gene from tobacco in ABA-signaling pathways.

A novel phosphate-induced gene, phi-2, has been identified by its induction on addition of phosphate to phosphate-starved tobacco BY-2 cells. The predicted gene product of phi-2 has significant homology to a group of bZIP proteins involved in ABA-signaling pathways, and phi-2 also responded to ABA treatment. A previously isolated phosphate-induced gene, phi-1, (Sano et al. (1999) Plant Cell Physiol. 40: 1) was also responsive to ABA. Although phosphate addition induced semi-synchronous cell division in phosphate-starved tobacco BY-2 cells, ABA adversely affected cell division. Detailed examination revealed that the high levels of phosphate required to induce semi-synchronous cell division seemed to be perceived as indicators of stress by the cells. One of the stress indicators perceived by the cells is a cytoplasmic pH change, to which phi-2 and phi-1 genes respond. The different components of the cell's response to phosphate induction are discussed.

Abscisic Acid↗
PubMed2004

A dehydration-induced NAC protein, RD26, is involved in a novel ABA-dependent stress-signaling pathway.

Arabidopsis thaliana RD26 cDNA, isolated from dehydrated plants, encodes a NAC protein. Expression of the RD26 gene was induced not only by drought but also by abscisic acid (ABA) and high salinity. The RD26 protein is localized in the nucleus and its C terminal has transcriptional activity. Transgenic plants overexpressing RD26 were highly sensitive to ABA, while RD26-repressed plants were insensitive. The results of microarray analysis showed that ABA- and stress-inducible genes are upregulated in the RD26-overexpressed plants and repressed in the RD26-repressed plants. Furthermore, RD26 activated a promoter of its target gene in Arabidopsis protoplasts. These results indicate that RD26 functions as a transcriptional activator in ABA-inducible gene expression under abiotic stress in plants.

Abscisic Acid↗
PubMed1998

Role of farnesyltransferase in ABA regulation of guard cell anion channels and plant water loss.

Desiccation of plants during drought can be detrimental to agricultural production. The phytohormone abscisic acid (ABA) reduces water loss by triggering stomatal pore closure in leaves, a process requiring ion-channel modulation by cytoplasmic proteins. Deletion of the Arabidopsis farnesyltransferase gene ERA1 or application of farnesyltransferase inhibitors resulted in ABA hypersensitivity of guard cell anion-channel activation and of stomatal closing. ERA1 was expressed in guard cells. Double-mutant analyses of era1 with the ABA-insensitive mutants abi1 and abi2 showed that era1 suppresses the ABA-insensitive phenotypes. Moreover, era1 plants exhibited a reduction in transpirational water loss during drought treatment.

Abscisic Acid↗
PubMedDate not supplied

Protein kinase cascade involved in rapid ABA-signaling in guard cells of Vicia faba.

Protein kinases are involved in signal transduction for environmental stress responses. In response to drought and salinity, a 48-kDa protein kinase (AAPK; abscisic acid-activated protein kinase (AAPK) in guard cells is activated by abscisic acid (ABA) and phosphorylates several targets such as the carboxy-terminus of inward-rectifying K+ channel and heterogeneous mRNA binding protein to adopt to the changing environment. The AAPK expressed specifically in guard cells, and recombinant AAPK was phosphorylated only with the extract from ABA-treated guard cells but not from untreated cells. This indicates the presence of an AAPK kinase (AAPKK), which is activated by ABA and phosphorylates AAPK preceding the activation of AAPK. Both AAPK and AAPKK are involved in the protein kinase cascade for the rapid ABA-signaling.

Cloning, Molecular↗