M. K. Walker-Simmons

Washington State University, Pullman, Washington, United States

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Publications (55)228.65 Total impact

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    ABSTRACT: An enantioselective synthesis of (+)-8′-demethyl ABA (2) is described. The chiral intermediate 7 was prepared by yeast reduction of a substituted monoprotected cyclohexa-2,5-dien-1,4-dione (9) synthesized through a phenol oxidation. The scope and limitations of the phenol oxidation is described. 8′-Demethyl ABA shows ABA-like activity in wheat embryo germination inhibition, showing that the 8′-methyl group is not essential for biological activity. Key words: abscisic acid, phenol oxidation, yeast reduction.
    No preview · Article · Feb 2011 · Canadian Journal of Chemistry
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Mar 2010 · ChemInform
  • M. K. Walker-Simmons · Lynn D. Holappa · Garth D. Abrams · Suzanne R. Abrams
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    ABSTRACT: In plants, metabolism of the plant hormone (+)-S-abscisic acid (ABA) occurs by oxidation at the 8′-carbon on the ABA ring, producing (+)-8′-hydroxy-ABA (8′OH-ABA), which undergoes ring closure to phaseic acid (PA), or at the 7′-carbon producing 7′-hydroxy-ABA (7′OH-ABA). New methods for synthesixing and stabilizing 8′OH-ABA have enabled us for the first time to compare the biological activities of the ABA metabolites. 8′OH-ABA. PA and 7′OH-ABA. Activities were determined in wheat (Triticum aestivum, cvs Brevor and Clarks Cream) using optically pure natural enantiomers of ABA. 8′OH-ABA, PA, and 7′OH-ABA. Comparison of wheat embryo germination inhibitory activity showed that only the metabolite 7′OH-ABA had significant activity (10 to 40% of effective ABA activity) as a germination inhibitor of wheat embryos. The metabolites had differential effects on ABA-responsive gene expression. Both 8′OH-ABA and PA were effective inducers of an ABA-responsive LEA (late embryogenesis abundant) gene, wheat group 3 LEA, in seedling roots, suggesting that ABA metabolites can maintain and prolong LEA gene expression. The metabolites had only a slight effect on accumulation of an ABA-responsive protein kinase (PKABA1) mRNA or pMA1951. These results are consistent with the idea that there are several control points in the ABA metabolic pathway and indicate that assessment of ABA signalling responses should include consideration of the biological activities of ABA metabolites.
    No preview · Article · Apr 2006 · Physiologia Plantarum

  • No preview · Article · Jul 2005 · Crop Science

  • No preview · Article · Jul 2005 · Crop Science
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    ABSTRACT: A new member of the cereal PKABA1 subfamily of protein kinases, TtPK1, was isolated from Triticum tauschii, a diploid progenitor of hexaploid wheat, Triticum aestivum. The full-length TtPK1 cDNA was cloned from a library derived from vegetative tissues from 26 d old light grown T. tauschii seedlings. TtPK1 cDNA hybridizes to transcripts that are upregulated in dehydrated leaves and are abundant in coleoptile tissue of 7 d old T. aestivum seedlings. TtPK1 mRNA has nucleotide identities of 82 and 79% to PKABA1 and TaPK3, respectively, and deduced amino acid sequence identities of 84 and 83% to PKABA1 and TaPK3, respectively. TtPK1 is similar to members of the SnRK2 subfamily of protein kinases in that it contains a unique acidic domain at the carboxyl terminus, and all twelve of the conserved subdomains found in serine/threonine protein kinases. Functional analyses of TtPK1 transiently over-expressed by bombarding barley half-grains showed that TtPK1 could suppress gibberellic acid inducible alpha-amylase gene expression, a suppressive activity similar to that of both PKABA1 and ABA. When transiently expressed in barley aleurone protoplasts, TtPK1-GFP accumulates in the nucleus and cytosol while a mutant TtPK1-GFP was localized only to the cytoplasm and vacuoles.
    Full-text · Article · May 2005 · Journal of Cereal Science
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    ABSTRACT: A total of 37 original cDNA libraries and 9 derivative libraries enriched for rare sequences were produced from Chinese Spring wheat (Triticum aestivum L.), five other hexaploid wheat genotypes (Cheyenne, Brevor, TAM W101, BH1146, Butte 86), tetraploid durum wheat (T. turgidum L.), diploid wheat (T. monococcum L.), and two other diploid members of the grass tribe Triticeae (Aegilops speltoides Tausch and Secale cereale L.). The emphasis in the choice of plant materials for library construction was reproductive development subjected to environmental factors that ultimately affect grain quality and yield, but roots and other tissues were also included. Partial cDNA expressed sequence tags (ESTs) were examined by various measures to assess the quality of these libraries. All ESTs were processed to remove cloning system sequences and contaminants and then assembled using CAP3. Following these processing steps, this assembly yielded 101,107 sequences derived from 89,043 clones, which defined 16,740 contigs and 33,213 singletons, a total of 49,953 "unigenes." Analysis of the distribution of these unigenes among the libraries led to the conclusion that the enrichment methods were effective in reducing the most abundant unigenes and to the observation that the most diverse libraries were from tissues exposed to environmental stresses including heat, drought, salinity, or low temperature.
    Full-text · Article · Oct 2004 · Genetics
  • Ryan L. Wagner · M.K. Walker-Simmons
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    ABSTRACT: An early difference in net protein phosphorylation activity occurred in dormant and after-ripened wheat (Triticum aestivum L.) grains within the first hour of imbibition at 30°C. Embryos from dry, dormant and after-ripened caryopses exhibited a high degree of protein phosphorylation, particularly of four proteins (68, 54, 51 and 42 kDa). Upon hydration, protein phosphorylation activity in dormant embryos decreased within 1 h and reached minimal phosphorylation activity by 5 h. Protein phosphorylation activity in after-ripened (germinable) embryos was not suppressed and remained high during germination. If the hydrated dormant embryos were dried, protein phosphorylation activity was restored. Application of the protein phosphatase inhibitor, okadaic acid, partially overcame dormancy and slowed the decrease in phosphorylation activity. These results suggested that reduction of protein phosphorylation activity slowed the rate of germination.
    No preview · Article · Aug 2004 · Seed Science Research
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    Russell R Johnson · Ryan L Wagner · Steven D Verhey · Mary K Walker-Simmons
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    ABSTRACT: The abscisic acid (ABA)-induced protein kinase PKABA1 is present in dormant seeds and is a component of the signal transduction pathway leading to ABA-suppressed gene expression in cereal grains. We have identified a member of the ABA response element-binding factor (ABF) family of basic leucine zipper transcription factors from wheat (Triticum aestivum) that is specifically bound by PKABA1. This protein (TaABF) has highest sequence similarity to the Arabidopsis ABA response protein ABI5. In two-hybrid assays TaABF bound only to PKABA1, but not to a mutant version of PKABA1 lacking the nucleotide binding domain, suggesting that binding of TaABF requires prior binding of ATP as would be expected for binding of a protein substrate by a protein kinase. TaABF mRNA accumulated together with PKABA1 mRNA during wheat grain maturation and dormancy acquisition and TaABF transcripts increased transiently during imbibition of dormant grains. In contrast to PKABA1 mRNA, TaABF mRNA is seed specific and did not accumulate in vegetative tissues in response to stress or ABA application. PKABA1 produced in transformed cell lines was able to phosphorylate synthetic peptides representing three specific regions of TaABF. These data suggest that TaABF may serve as a physiological substrate for PKABA1 in the ABA signal transduction pathway during grain maturation, dormancy expression, and ABA-suppressed gene expression.
    Preview · Article · Nov 2002 · Plant physiology
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    QX Shen · Aurelio Gomez-Cadenas · PG Zhang · Mary Kay Walker-Simmons · Jen Sheen · T.-H.D. Ho
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    ABSTRACT: Abscisic acid (ABA) induces genes that are highly expressed during late embryogenesis, but suppresses gibberellin (GA)-responsive genes essential for seed germination and seedling growth. Promoter elements necessary and sufficient for ABA up- and down-regulation of gene expression have been previously defined in barley aleurone layers. We have studied the effect of a protein phosphatase 2C, ABI1, an ABA-inducible protein kinase, PKABA1, and a transcription factor, VP1, on ABA action in a barley aleurone transient expression system. The observations have allowed us to dissect ABA signal transduction pathways leading to either induction or suppression of gene expression. The ABA induction of embryogenesis genes is highly inhibited in the presence of a mutated protein phosphatase 2C, encoded by the abi1-1 dominant mutant gene that is known to block ABA responses in Arabidopsis. However, the abi1-1 gene product has no effect on the ABA suppression of a GA-responsive alpha-amylase gene. On the other hand, PKABA1 suppresses the expression of alpha-amylase genes, but has little effect on ABA up-regulated genes. Therefore, it appears that ABA induction and suppression follow two separate signal transduction pathways with the former inhibited by ABI1 and the latter modulated by PKABA1. The presence of VP1 enhances the ABA induction of late embryogenesis genes, but also suppresses germination specific genes. A schematic model based on these observations is presented to explain the effect of these regulatory proteins on ABA-mediated gene expression.
    Preview · Article · Nov 2001 · Plant Molecular Biology
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    Aurelio Gomez-Cadenas · Rodolfo Zentella · Mary Kay Walker-Simmons · T.-H.D. Ho
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    ABSTRACT: The antagonism between gibberellins (GA) and abscisic acid (ABA) is an important factor regulating the developmental transition from embryogenesis to seed germination. In barley aleurone layers, the expression of genes encoding alpha-amylases and proteases is induced by GA but suppressed by ABA. It has been shown that an ABA-induced protein kinase, PKABA1, mediates the ABA suppression of alpha-amylase expression. Using a barley aleurone transient expression system, we have now localized the site of action of PKABA1 relative to other signal transduction components governing the expression of alpha-amylase. The expression of alpha-amylase can be transactivated by the transcription factor GAMyb, which is itself induced by GA. A truncated GAMyb containing the DNA binding domain but lacking the transactivation domain prevents the GA induction of alpha-amylase, further supporting the notion that GAMyb mediates the GA induction of alpha-amylase expression. Although ABA and PKABA1 strongly inhibit the GA induction of alpha-amylase, they have no effect on GAMyb-transactivated alpha-amylase expression. Using a GAMyb promoter--beta-glucuronidase construct, we also show that both ABA and PKABA1 repress the GA induction of GAMyb. In the slender mutant, GAMyb and alpha-amylase are highly expressed, even in the absence of GA. However, this constitutive expression can still be inhibited by ABA, PKABA1, or an inhibitor of cGMP synthesis. On the basis of these observations, we suggest that PKABA1 acts upstream from the formation of functional GAMyb but downstream from the site of action of the Slender gene product. Because PKABA1 inhibits the GA induction of the GAMyb promoter--beta-glucuronidase construct, it appears that at least part of the action of PKABA1 is to downregulate GAMyb at the transcriptional level.
    Full-text · Article · Apr 2001 · The Plant Cell
  • M K Walker-Simmons · P A Rose · L R Hogge · S R Abrams
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    ABSTRACT: Development of monoclonal antibodies (MAbs) that specifically recognize the plant hormone, (+)-(S)-abscisic acid (ABA) have enabled the development of ABA immunoassays (1,2). ABA measurement with these immunoassays is efficient, sensitive, and suitable for large numbers of samples (reviewed in ref. 3).
    No preview · Article · Feb 2000 · Methods in Molecular Biology
  • R.E. Allan · C.F. Morris · R.F. Line · J.A. Anderson · M.K. Walker-simmons · E. Donaldson

    No preview · Article · Jan 2000 · Crop Science
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    A Gómez-Cadenas · S.D. Verhey · L.D. Holappa · Q.X. Shen · T.-H. D. Ho · M.K. Walker-Simmons
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    ABSTRACT: The phytohormone abscisic acid (ABA) induces genes-encoding proteins involved in desiccation tolerance and dormancy in seeds, but ABA also suppresses gibberellin (GA)-responsive genes encoding hydrolytic enzymes essential for postgermination growth. A unique serine/threonine protein kinase, PKABA1 mRNA, up-regulated by ABA in seeds, has been identified. In this report, the effect of PKABA1 on the signal transduction pathway mediating ABA induction and suppression of genes has been determined in aleurone layers of barley seeds. Two groups of gene constructs were introduced to barley aleurone layers by using particle bombardment: the reporter constructs containing the coding sequence of beta-glucuronidase gene linked to hormone-responsive promoters and the effector constructs containing the coding region of protein kinases linked to a constitutive promoter. Constitutive expression of PKABA1 drastically suppressed expression of low- and high-pI alpha-amylase and protease genes induced by GA. However, the presence of PKABA1 had only a small effect on the ABA induction of a gene encoding a late embryogenesis abundant protein, HVA1. Our results indicate that PKABA1 acts as a key intermediate in the signal transduction pathway leading to the suppression of GA-inducible gene expression in cereal aleurone layers.
    Preview · Article · Mar 1999 · Proceedings of the National Academy of Sciences
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    A M Donoghue · M K Walker-Simmons
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    ABSTRACT: Dehydration-induced proteins and other osmo-protectants enable plants to survive dehydration stress. The object of this study was to determine whether dehydration-induced proteins from wheat seeds could protect turkey sperm and improve survival and function after liquid storage. A partially purified heat-soluble protein extract was isolated from dry, mature wheat seed embryos and added to semen diluent. Hens were inseminated with either fresh or semen stored 24 h at 5 C and fertility and hatchability data collected. The addition of 10% wheat protein extract to semen stored 24 h at 5 C improved fertility and hatchability of eggs over semen stored in diluent alone (P < 0.05). The heat-soluble proteins isolated from wheat seed embryos are capable of protecting turkey sperm during in vitro storage and could potentially improve long-term storage of sperm from other species.
    Preview · Article · Feb 1999 · Poultry Science
  • M. K. Walker-Simmons
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    ABSTRACT: Reversible phosphorylation is catalysed by protein kinases that transfer the γ-phosphate from ATP to amino acid residues of proteins. The process can be reversed by protein phosphatases. Phosphorylation can dramatically activate or inhibit enzymes and affect protein-protein interaction. Through phosphorylation protein kinases can amplify and propagate cellular signals. In plants and now seeds, protein kinases involved in hormone, defence and environmental stress responses are being identified. Increasingly, these protein kinases are being cloned and characterized, demonstrating the major role of reversible protein phosphorylation in seeds.
    No preview · Article · May 1998 · Seed Science Research
  • Eric W. Storlie · R. E. Allan · M. K. Walker-Simmons
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    ABSTRACT: We investigated the feasibility of cold hardiness manipulation in wheat, Triticum aestivum L, with the Vrn1-Fr1 interval on chromosome 5AL. The interval contains a gene(s) that has influenced vernalization requirements and cold hardiness levels. We conducted LT50 tests (lethal temperature of 50% of plants) on wheat NILs (near-isogenic lines) that differed for alleles at the Vrn1-Fr1 interval, to determine the effects of the interval on cold hardiness levels between hardy and nonhardy wheat. The NILs were derived from five back-crosses between a spring wheat recurrent parent, 'Marfed', and two winter wheat donor parents, 'Suweon 185' and 'Chugoku 81', hardy and nonhardy, respectively. The developed populations were Suweon 185/6*Marfed and Chugoku 81/6*Marfed spring and winter NILs. Results showed that the winter NILs could tolerate a 4.3 °C colder LT50 score than the spring NILs, and that the Suweon 185/6*Marfed winter NILs could tolerate a 0.5 °C colder LT50 than Chugoku 81/6*Marfed winter NILs. Results indicate that the Vrn1-Fr1 interval explained between 71 and 91% of the variation for LT50 scores between these genotypes. The NILs were analyzed with the probe Xwg644 to confirm linkage with the Vrn1-Fr1 interval and in determine its utility as a marker for vernalization requirement and cold hardiness. EcoRI-digested DNA of the winter and spring NIL wheat, probed with Xwg644, showed that a 9.7-kb band co-segregated with the winter growth habit. Results indicate that differences in cold hardiness levels between winter wheat cultivars may be explained by this interval and that the interval may be manipulated through plant breeding to improve the cold hardiness of cultivars.
    No preview · Article · Mar 1998 · Crop Science
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    S. R. Abrams · P. A. Rose · A. J. Cutler · J. J. Balsevich · B. Lei · M. K. Walker-Simmons
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    ABSTRACT: We report here the synthesis and biological activity of a new persistent abscisic acid (ABA) analog, 8[prime]-methylene ABA. This ABA analog has one additional carbon atom attached through a double bond to the 8[prime]-carbon of the ABA molecule. (+)-8[prime]-Methylene ABA is more active than the natural hormone (+)-ABA in inhibiting germination of cress seed and excised wheat embryos, in reducing growth of suspension-cultured corn cells, and in reducing transpiration in wheat seedlings. The (+)-8[prime]-methylene analog is slightly weaker than (+)-ABA in increasing expression of ABA-inducible genes in transgenic tobacco, but is equally active in stimulating a transient elevation of the pH of the medium of corn cell cultures. In corn cells, both (+)-ABA and (+)-8[prime]-methylene ABA are oxidized at the 8[prime] position. ABA is oxidized to phaseic acid and (+)-8[prime]-methylene ABA is converted more slowly to two isomeric epoxides. The alteration in the ABA structure causes the analog to be metabolized more slowly than ABA, resulting in longer-lasting and more effective biological activity relative to ABA.
    Preview · Article · Jun 1997 · Plant physiology
  • Christina Walters · Jeffrey L. Ried · M. K. Walker-Simmons
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    ABSTRACT: Late embryogenesis abundant (LEA) proteins accumulate in developing seeds prior to maturation drying and are presumed to help protect embryos from desiccation stress. The unusual solubility properties of these proteins, such as resistance to heat coagulation, have led to suggestions that they alter the hydration properties of cellular constituents. Hydration characteristics and water potential range at which wheat heat-soluble LEA proteins were expressed have been determined. Levels of heatsoluble proteins decline in germinating seeds but can be induced by dehydration (ψ ≤ −0.5 MPa) in crown meristematic tissue that is desiccation tolerant. The heatsoluble extract from mature wheat embryos contained proteins and sugars at about a 1:1 (w/w) ratio. Only about half of the sugars could be removed by exhaustive dialysis; the rest appeared to be tightly associated with the proteins. The water sorption characteristics of undialysed and dialysed heat-soluble protein/sugar fractions were compared with other water-soluble proteins (bovine serum albumin, lysozyme or gluten) and with sucrose. At relative humidities greater than 50%, the amount of water absorbed by protein-sugar mixes was a function of the sugar content. For the same sugar content, the heat-soluble protein preparation absorbed 2–3 times more water than a lysozyme/sucrose preparation. The rate at which heat-soluble protein fractions dried was also different to desorption rates of lysozyme/sucrose mixes. While lysozyme/sucrose mixtures dried either very rapidly (within 20 min) or very slowly (about 2 months) depending on the sugar content, desorption rates of the heat soluble protein-sugar preparations were intermediate (2–10 days) and modulated by sugar concentration. Based on the presumption that the hydrophilic properties of LEA heat-soluble proteins are important to their function, it is suggested that these proteins function to control drying so that cells stay at critical water potentials for the proper time. In this respect, the heat-soluble LEA proteins do not prevent desiccation, but serve as hydration buffers.
    No preview · Article · May 1997 · Seed Science Research
  • Lynn D. Holappa · M K Walker-Simmons
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    ABSTRACT: We have identified a new wheat PKABA1-like protein kinase gene, TaPK3, that is expressed in greening wheat seedlings. TaPK3 has high sequence homology (97% similarity with some sequence diversity at the 3' end) to the wheat PKABA1 protein kinase mRNA, which is upregulated by cold-temperature treatment, dehydration and abscisic acid (ABA). Use of a TaPK3 gene-specific probe has revealed that TaPK3 is differentially expressed with respect to PKABA1. TaPK3 mRNA accumulates in greening shoot tissue of wheat, but is not affected by dehydration, cold-temperature treatment or ABA. Based on sequence and expression differences, we conclude that expression of the PKABA1-like protein kinases is not limited to stress responses.
    No preview · Article · Apr 1997 · Plant Molecular Biology

Publication Stats

2k Citations
228.65 Total Impact Points


  • 1977-2006
    • Washington State University
      • • Department of Crop and Soil Sciences
      • • Institute of Biological Chemistry
      • • Department of Plant Pathology
      Pullman, Washington, United States
  • 2004
    • Iowa State University
      • Department of Genetics, Development and Cell Biology
      Ames, IA, United States
  • 1991
    • Agricultural Research Service
      Kerrville, Texas, United States