Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channels that
are the predominant neuroreceptors in the mammalian brain. Genes with high
sequence similarity to animal iGluRs have been identified in Arabidopsis. T
o understand the role of Arabidopsis glutamate receptor-like (AK;LR) genes
in plants, we have taken a pharmacological approach by examining the effect
s of BMAA [S(+)-beta -methyl-alpha, beta -diaminopropionic acid], a cycad-d
erived iGluR agonist, on Arabidopsis morphogenesis. When applied to Arabido
psis seedlings, BMAA caused a 2- to 3-fold increase in hypocotyl elongation
and inhibited cotyledon opening during early seedling development. The eff
ect of BMAA on hypocotyl elongation is light specific. Furthermore, BMAA ef
fects on early morphogenesis of Arabidopsis can be reversed by the simultan
eous application of glutamate, the native iGluR agonist in animals. To dete
rmine the targets of BMAA action in Arabidopsis, a genetic screen was devis
ed to isolate Arabidopsis mutants with a BMAA insensitive morphology (bim).
When grown in the light on BMAA, bim mutants exhibited short hypocotyls co
mpared with wild type. bim mutants were grouped into three classes based on
their morphology when grown in the dark in the absence of BMAA. Class-I bi
m mutants have a normal, etiolated morphology, similar to wild-type plants.
Class-II bim mutants have shorter hypocotyls and closed cotyledons when gr
own in the dark. Class-III bim mutants have short hypocotyls and open cotyl
edons when grown in the dark, resembling the previously characterized const
itutively photomorphogenic mutants (cop, det, Jus, and shy). Further analys
is of the bim mutants should help define whether plant-derived iGluR agonis
ts target glutamate receptor signaling pathways in plants.