Glutamate receptor-like genes form Ca²⁺ channels in pollen tubes and are regulated by pistil D-serine

Abstract

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 genes (GLRs) facilitate Ca2+ influx across the plasma membrane, modulate apical [Ca2+]cyt gradient and consequently 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 analogous to amino acid–mediated communication commonly observed in animal nervous systems.