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Abstract The phytohormone ethylene has numerous effects on plant growth and development. Its immediate precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), is a non-proteinogenic amino acid produced by ACC SYNTHASE (ACS). ACC is often used to induce ethylene responses. Here, we demonstrate that ACC exhibits ethylene-independent signaling in
Arabidopsis thaliana reproduction. By analyzing anacs octuple mutant with reduced seed set, we find that ACC signaling in ovular sporophytic tissue is involved in pollen tube attraction, and promotes secretion of the pollen tube chemoattractant LURE1.2. ACC activates Ca2+-containing ion currents via GLUTAMATE RECEPTOR-LIKE (GLR) channels in root protoplasts. In COS-7 cells expressing mossPp GLR1, ACC induces the highest cytosolic Ca2+elevation compared to all twenty proteinogenic amino acids. In ovules, ACC stimulates transient Ca2+elevation, and Ca2+influx in octuple mutant ovules rescues LURE1.2 secretion. These findings uncover a novel ACC function and provide insights for unraveling new physiological implications of ACC in plants. -
Summary We investigated the molecular basis and physiological implications of anion transport during pollen tube (
PT ) growth inArabidopsis thaliana (Col‐0).Patch‐clamp whole‐cell configuration analysis of pollen grain protoplasts revealed three subpopulations of anionic currents differentially regulated by cytoplasmic calcium ([Ca2+]cyt). We investigated the pollen‐expressed proteins
At SLAH 3,At ALMT 12,At TMEM 16 andAt CCC as the putative anion transporters responsible for these currents.At CCC ‐GFP was observed at the shank andAt SLAH 3‐GFP at the tip and shank of thePT plasma membrane. Both are likely to carry the majority of anion current at negative potentials, as extracellular anionic fluxes measured at the tip ofPT s with an anion vibrating probe were significantly lower inslah3 −/− andccc −/− mutants, but unaffected inalmt12 −/− andtmem16 −/− . We further characterised the effect ofpH andGABA by patch clamp. Strong regulation by extracellularpH was observed in the wild‐type, but not intmem16 −/− . Our results are compatible withAt TMEM 16 functioning as an anion/H+cotransporter and therefore, as a putativepH sensor.GABA presence: (1) inhibited the overall currents, an effect that is abrogated in thealmt12 −/− and (2) reduced the current inAt ALMT 12 transfectedCOS ‐7 cells, strongly suggesting the direct interaction ofGABA withAt ALMT12.Our data show that
At SLAH 3 andAt CCC activity is sufficient to explain the major component of extracellular anion fluxes, and unveils a possible regulatory system linkingPT growth modulation bypH ,GABA , and [Ca2+]cytthrough anionic transporters.