GLUTAMATE RECEPTOR-LIKE channels are essential for chemotaxis and reproduction in mosses

Glutamate receptors are well characterized channels that mediate cell-to-cell communication during neurotransmission in animals, but their functional role in organisms without a nervous system remains unclear. In plants, genes of the GLUTAMATE RECEPTOR-LIKE (GLR) family have been implicated in defence against pathogens, reproduction, control of stomata aperture and light signal transduction. However, the large number of GLR genes present in angiosperm genomes (20 to 70) has prevented the observation of strong phenotypes in loss-of-function mutants. Here we show that in the basal land plant Physcomitrella patens, mutation of the GLR genes GLR1 and GLR2 causes failure of sperm cells to target the female reproductive organs. In addition, we show that GLR genes encode non-selective Ca²⁺-permeable channels that can regulate cytoplasmic Ca²⁺ and are needed to induce the expression of a BELL1-like transcription factor essential for zygote development. Our work reveals functions for GLR channels in sperm chemotaxis and transcriptional regulation. Sperm chemotaxis is essential for fertilization in both animals and early land plants such as bryophytes and pteridophytes. Therefore, our results suggest that ionotropic glutamate receptors may have been conserved throughout plant evolution to mediate cell-to-cell communication during sexual reproduction.