Dual localization of plant glutamate receptor AtGLR3.4 to plastids and plasmamembrane

Abstract

Bioinformatic approaches have allowed the identification in Arabidopsis thaliana of twenty genes encoding for homologues of animal ionotropic glutamate receptors (iGLRs). Some of these putative receptor proteins, grouped into three subfamilies, have been located to the plasmamembrane, but their possible location in organelles has not been investigated so far. In the present work we provide multiple evidence for the plastid localization of a glutamate receptor, AtGLR3.4, in Arabidopsis and tobacco. Biochemical analysis was performed using an antibody shown to specifically recognize both the native protein in Arabidopsis and the recombinant AtGLR3.4 fused to YFP expressed in tobacco. Western blots indicate the presence of AtGLR3.4 in both the plasmamembrane and in chloroplasts. In agreement, in transformed Arabidopsis cultured cells as well as in agroinfiltrated tobacco leaves, AtGLR3.4::YFP is detected both at the plasmamembrane and at the plastid level by confocal microscopy. The photosynthetic phenotype of mutant plants lacking AtGLR3.4 was also investigated. These results identify for the first time a dual localization of a glutamate receptor, revealing its presence in plastids and chloroplasts and opening the way to functional studies.

Ca2+ Conduction by an Amino Acid-Gated Ion Channel Related to Glutamate Receptors

“…1D). No evidence of chloroplast localization of GLR3.4 reported in a study that also reported plasma membrane localization (Teardo et al, 2011) was detected, though intense chlorophyll fluorescence could have masked a weak GFP signal.…”

Plant Calcium-Permeable Channels

“…Although both of these plasma membrane proteins reside at the sieve plate in roots, their activities ultimately manifest in the pericycle with a regulatory effect on the production of lateral root primordia (Vincill et al, 2013). The finding that AtGLR3.4 can reside in the chloroplast (Teardo et al, 2011), although not confirmed by Vincill et al (2012), raises further opportunities and challenges for the GLR community. The question remains whether the concentrations of amino acids used in assays would occur in planta (Vincill et al, 2012); many studies use concentrations of ligand higher than would be expected outside of cells.…”

“…As mentioned earlier, there are now indications of CNGC residence at the tonoplast, GLR residence at the chloroplast, and MSL residence in chloroplasts (Teardo et al, 2011;Veley et al, 2012;Yuen and Christopher, 2013). The chloroplast protein translocon TIC complex conducts K + in PLB, and its capacity for Ca 2+ conduction now needs to be explored (Kikuchi et al, 2013).…”

Signalling via glutamate and GLRs in Arabidopsis thaliana

“…Therefore, integration into the plasma membrane seems to be likely (Lam et al 1998;Chiu et al 1999;Nagata 2004;Teardo et al 2010). Besides the signal sequences for the secretory pathway, mitochondrial and chloroplast targeting sequences can be found (Teardo et al 2010(Teardo et al , 2011. When looking at clade III in A. thaliana, four of seven receptors (AtGLR3.1, 3.2, 3.6 and AtGLR3.7) are supposed to enter the secretory pathway while the three others (AtGLR3.3, 3.4 and 3.5) contain multiple targeting sequences (Teardo et al 2010(Teardo et al , 2011.…”