The Presence of a Heterotrimeric G Protein and Its Role in Signal Transduction of Extracellular Calmodulin in Pollen Germination and Tube Growth

Abstract

The role of heterotrimeric G proteins in pollen germination, tube growth, and signal transduction of extracellular calmodulin (CaM) was examined in lily pollen. Two kinds of antibodies raised against animal Gz ␣ , one against an internal sequence and the other against its N terminus, cross-reacted with the same 41-kD protein from lily pollen plasma membrane. This 41-kD protein was also specifically ADP ribosylated by pertussis toxin. Microinjection of the membrane-impermeable G protein agonist GTP-␥ -S into a pollen tube increased its growth rate, whereas microinjection of the membrane-impermeable G protein antagonist GDP-␤ -S and the anti-G ␣ antibody decreased pollen tube growth. The membrane-permeable G protein agonist cholera toxin stimulated pollen germination and tube growth. Anti-CaM antiserum inhibited pollen germination and tube growth, and this inhibitory effect was completely reversed by cholera toxin. The membrane-permeable heterotrimeric G protein antagonist pertussis toxin completely stopped pollen germination and tube growth. Purified CaM, when added directly to the medium of plasma membrane vesicles, significantly activated GTPase activity in plasma membrane vesicles, and this increase in GTPase activity was completely inhibited by pertussis toxin and the nonhydrolyzable GTP analogs GTP-␥ -S and guanylyl-5 Ј -imidodiphosphate. The GTPase activity in plasma membrane vesicles was also stimulated by cholera toxin. These data suggest that heterotrimeric G proteins may be present in the pollen system where they may be involved in the signal transduction of extracellular CaM and in pollen germination and tube growth.

Calcium promotes activity and confers heat stability on plant peroxidases

“…44 In addition, apoplastic calmodulin plays an important role in signal transduction. [45][46][47] Here, we show that the calcium response of Fractionation of the maize extract by gel filtration reveals two distinct peaks of PO activity ( Fig. 7) representing low and high molecular mass species.…”

Site-directed mutagenesis of the Arabidopsis heterotrimeric G protein β subunit suggests divergent mechanisms of effector activation between plant and animal G proteins

“…Using Clustal W (Larkin et al 2007), we generated a multiple alignment of several subunits from animals and plants to examine the level of conservation of speciWc amino acid residues. G proteins have been linked to CaM-mediated signaling in stomatal closure (Chen et al 2004;Li et al 2009) and pollen tube growth (Ma et al 1999), and it has been shown that an N-terminal motif of human subunits is able to bind CaM (Liu et al 1997). CaM-binding domains such as those of human subunits generally take the form of an -helix with several basic residues (lysine, arginine or histidine) on the CaM-binding surface.…”

Characterization of a cDNA coding for an extracellular calmodulin-binding protein from suspension-cultured cells of Angelica dahurica

“…A series of experiments have been done in laboratories (including ours) to provide evidences that the presence of CaM in the cell wall area is universal Chen et al 2003), and further work indicates that extracellular CaM plays several important roles in the plant kingdom, such as: promoting the proliferation of suspension-cultured cells and its protoplasts (Sun et al 1994;Sun et al 1995;Zhao and Zhu 1996), regulating pollen germination and tube growth (Ma and Sun 1997), and inducing light-independent rbcS gene expression (Zhou et al 2001). With the unveiling of the transmembrane signaling transduction mechanism (Ma et al 1999;Wang et al 2000;Shang et al 2003), we put forward a view that extracellular CaM may be a polypeptide signal in plants (Sun et al 1998;Ma et al 1999;Sun and Ma 2001).…”