title: Self-incompatibility in Papaver rhoeas activates nonspecific cation conductance permeable to Ca2+ and K+.
abstract: Cellular responses rely on signaling. In plant cells, cytosolic free calcium is a major second messenger, and ion channels play a key role in mediating physiological responses. Self-incompatibility (SI) is an important genetically controlled mechanism to prevent self-fertilization. It uses interaction of matching S-determinants from the pistil and pollen to allow "self" recognition, which triggers rejection of incompatible pollen. In Papaver rhoeas, the S-determinants are PrsS and PrpS. PrsS is a small novel cysteine-rich protein; PrpS is a small novel transmembrane protein. Interaction of PrsS with incompatible pollen stimulates S-specific increases in cytosolic free calcium and alterations in the actin cytoskeleton, resulting in programmed cell death in incompatible but not compatible pollen. Here, we have used whole-cell patch clamping of pollen protoplasts to show that PrsS stimulates SI-specific activation of pollen grain plasma membrane conductance in incompatible but not compatible pollen grain protoplasts. The SI-activated conductance does not require voltage activation, but it is voltage sensitive. It is permeable to divalent cations (Ba(2+) ≥ Ca(2+) > Mg(2+)) and the monovalent ions K(+) and NH(4)(+) and is enhanced at voltages negative to -100 mV. The Ca(2+) conductance is blocked by La(3+) but not by verapamil; the K(+) currents are tetraethylammonium chloride insensitive and do not require Ca(2+). We propose that the SI-stimulated conductance may represent a nonspecific cation channel or possibly two conductances, permeable to monovalent and divalent cations. Our data provide insights into signal-response coupling involving a biologically important response. PrsS provides a rare example of a protein triggering alterations in ion channel activity.
authors.affiliation: School of Biosciences , University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Juyou
authors.initials: J
authors.lastname: Wu
authors.forename: Su
authors.initials: S
authors.lastname: Wang
authors.forename: Yuchun
authors.initials: Y
authors.lastname: Gu
authors.forename: Shaoling
authors.initials: S
authors.lastname: Zhang
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Publicover
authors.forename: Vernonica E
authors.initials: VE
authors.lastname: Franklin-Tong
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability; D007473:Ion Channels / Q000378:metabolism*; D017136:Ion Transport; D010207:Papaver / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000378:metabolism*; D011058:Pollen / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D011523:Protoplasts / Q000502:physiology; D057945:Self-Fertilization; D015398:Signal Transduction
chemical_list: D007473:Ion Channels; D010940:Plant Proteins; D011188:Potassium; D002118:Calcium