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SLAC1-related signal transduction pathway involved in ABA- induced stomatal closure and K⁺ selective transport by the OsHKT2;4 transporter from rice (Oryza sativa) with atypical Na⁺ transport properties and competition in permeation of K⁺ over Mg²⁺ and Ca²⁺ ions

  • Author(s): Brodsky, Dennis E.
  • et al.
Abstract

ABA is a phytohormone known to play a major role in plant development and the plant stress response. SLAC1, the first anion channel discovered in plants, lies towards the end of the ABA signaling pathway. To analyze SLAC1-related ABA signaling, anion channel activity was measured in Xenopus laevis oocytes. Certain protein kinases were able to activate SLAC1 activity in oocytes, and the PP2C phosphatase ABI1 was able to inhibit these kinase- activated SLAC1 currents. When ABA and receptor PYR1 were added to the above components, SLAC1 activity was restored due to putative inhibition of ABI1. Mutations in SLAC1 and ABI1 had notable effects on SLAC1 channel activity in oocytes. Na⁺ and K⁺ homeostasis plays a crucial role in plant development and growth. A major group of plant Na⁺ and Na⁺/K⁺ transporters involved in salinity tolerance is the HKT family. HKT transporters are characterized into two major classes, based on structure as well as ion selectivity. The ion selectivity of class II OsHKT2;4 from Oryza sativa rice was studied in yeast and oocytes, and its localization was identified in Arabidopsis mesophyll protoplasts. Unlike typical class II HKT transporters, OsHKT2;4 is believed to be a K⁺ transporter with little dependence on Na⁺. OsHKT2;4, and TaHKT2;1 from wheat were found to be permeable to divalent cations. Cation competition experiments demonstrated that OsHKT2;4 and TaHKT2;1 have a higher selectivity for K⁺ or Na⁺/K⁺ respectively over these divalent cations, suggesting that Ca²⁺ and Mg²⁺ transport is small and dependent on plant K⁺ concentrations in vivo

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