Katy M Coxon

Publications (3)17.97 Total impact

• Source

  Available from: Lourdes Rubio

  Article: Arabidopsis annexin1 mediates the radical-activated plasma membrane Ca²+- and K+-permeable conductance in root cells.

  Anuphon Laohavisit, Zhonglin Shang, Lourdes Rubio, Tracey A Cuin, Anne-Aliénor Véry, Aihua Wang, Jennifer C Mortimer, Neil Macpherson, Katy M Coxon, Nicholas H Battey, Colin Brownlee, Ohkmae K Park, Hervé Sentenac, Sergey Shabala, Alex A R Webb, Julia M Davies
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  ABSTRACT: Plant cell growth and stress signaling require Ca²⁺ influx through plasma membrane transport proteins that are regulated by reactive oxygen species. In root cell growth, adaptation to salinity stress, and stomatal closure, such proteins operate downstream of the plasma membrane NADPH oxidases that produce extracellular superoxide anion, a reactive oxygen species that is readily converted to extracellular hydrogen peroxide and hydroxyl radicals, OH•. In root cells, extracellular OH• activates a plasma membrane Ca²⁺-permeable conductance that permits Ca²⁺ influx. In Arabidopsis thaliana, distribution of this conductance resembles that of annexin1 (ANN1). Annexins are membrane binding proteins that can form Ca²⁺-permeable conductances in vitro. Here, the Arabidopsis loss-of-function mutant for annexin1 (Atann1) was found to lack the root hair and epidermal OH•-activated Ca²⁺- and K⁺-permeable conductance. This manifests in both impaired root cell growth and ability to elevate root cell cytosolic free Ca²⁺ in response to OH•. An OH•-activated Ca²⁺ conductance is reconstituted by recombinant ANN1 in planar lipid bilayers. ANN1 therefore presents as a novel Ca²⁺-permeable transporter providing a molecular link between reactive oxygen species and cytosolic Ca²⁺ in plants.
  The Plant Cell 04/2012; 24(4):1522-33. · 8.99 Impact Factor
• Article: Heme-independent soluble and membrane-associated peroxidase activity of a Zea mays annexin preparation.

  Jennifer C Mortimer, Katy M Coxon, Anuphon Laohavisit, Julia M Davies
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  ABSTRACT: Annexins are cytosolic proteins capable of reversible, Ca(2+)-dependent membrane binding or insertion. Animal annexins form and regulate Ca(2+)-permeable ion channels and may therefore participate in signaling. Zea mays (maize) annexins (ZmANN33 and ZmANN35) have recently been shown to form a Ca(2+)-permeable conductance in planar lipid bilayers and also exhibit in vitro peroxidase activity. Peroxidases form a superfamily of intra- or extracellular heme-containing enzymes that use H(2)O(2) as the electron acceptor in a number of oxidative reactions. Maize annexin peroxidase activity appears independent of heme and persists after membrane association, the latter suggesting a role in reactive oxygen species signaling.
  Plant signaling & behavior 05/2009; 4(5):428-30.
• Article: Zea mays annexins modulate cytosolic free Ca2+ and generate a Ca2+-permeable conductance.

  Anuphon Laohavisit, Jennifer C Mortimer, Vadim Demidchik, Katy M Coxon, Matthew A Stancombe, Neil Macpherson, Colin Brownlee, Andreas Hofmann, Alex A R Webb, Henk Miedema, Nicholas H Battey, Julia M Davies
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  ABSTRACT: Regulation of reactive oxygen species and cytosolic free calcium ([Ca(2+)](cyt)) is central to plant function. Annexins are small proteins capable of Ca(2+)-dependent membrane binding or membrane insertion. They possess structural motifs that could support both peroxidase activity and calcium transport. Here, a Zea mays annexin preparation caused increases in [Ca(2+)](cyt) when added to protoplasts of Arabidopsis thaliana roots expressing aequorin. The pharmacological profile was consistent with annexin activation (at the extracellular plasma membrane face) of Arabidopsis Ca(2+)-permeable nonselective cation channels. Secreted annexins could therefore modulate Ca(2+) influx. As maize annexins occur in the cytosol and plasma membrane, they were incorporated at the intracellular face of lipid bilayers designed to mimic the plasma membrane. Here, they generated an instantaneously activating Ca(2+)-permeable conductance at mildly acidic pH that was sensitive to verapamil and Gd(3+) and had a Ca(2+)-to-K(+) permeability ratio of 0.36. These results suggest that cytosolic annexins create a Ca(2+) influx pathway directly, particularly during stress responses involving acidosis. A maize annexin preparation also demonstrated in vitro peroxidase activity that appeared independent of heme association. In conclusion, this study has demonstrated that plant annexins create Ca(2+)-permeable transport pathways, regulate [Ca(2+)](cyt), and may function as peroxidases in vitro.
  The Plant Cell 03/2009; 21(2):479-93. · 8.99 Impact Factor