Glutamate Receptor-Like Genes Form Ca2+ Channels in Pollen Tubes and Are Regulated by Pistil D-Serine

Elevations in cytosolic free calcium concentration ([Ca2+](cyt)) constitute a fundamental signal transduction mechanism in eukaryotic cells, but the molecular identity of Ca2+ channels initiating this signal in plants is still under debate. Here, we show by pharmacology and loss-of-function mutants that in tobacco and Arabidopsis, glutamate receptor-like channels (GLRs) facilitate Ca2+ influx across the plasma membrane, modulate apical [Ca2+] cyt gradient, and consequently affect pollen tube growth and morphogenesis. Additionally, wild-type pollen tubes grown in pistils of knock-out mutants for serine-racemase (SR1) displayed growth defects consistent with a decrease in GLR activity. Our findings reveal a novel plant signaling mechanism between male gametophyte and pistil tissue similar to amino acid-mediated communication commonly observed in animal nervous systems.