GTPγS antagonizes the mastoparan‐induced in vitro activity of PIP₂‐phospholipase C from symbiotic root nodules of Phaseolus vulgaris

Abstract

Phospholipase C (PLC) has been suggested to have a role in signal perception by Nod factors (NFs) in legume root hair cells. For instance, mastoparan, a well-described agonist of heterotrimeric G protein, induces nodulin expression after NFs treatment or Rhizobium inoculation. Furthermore, it has been recently demonstrated that mastoparan also mimics calcium oscillations induced by NFs, suggesting that PLC could play a key role during the nodulation process. In this study, we elucidate a biochemical relationship between PLC and heterotrimeric G proteins during NFs signaling in legumes. In particular, the effect of NFs on in vitro PLC activity from nodule membrane fractions in the presence of guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) and mastoparan was assayed. Our results indicate that for phosphatidylinositol 4,5 bisphosphate (PIP(2))-PLC, there is a specific activity of 20-27 nmol mg(-1) min(-1) in membrane fractions of nodules 18-20 days after inoculation with Rhizobium tropici. Interestingly, in the presence of 5 microM mastoparan, PIP(2)-PLC activity was almost double the basal level. In contrast, PIP(2)-PLC activity was downregulated by 1-10 microM GTPgammaS. Also, PLC activity was decreased by up to 64% in the presence of increasing concentrations of NFs (10(-8) to 10(-5) M). NFs are critical signaling molecules in rhizobia/legume symbiosis that can activate many of the plant's early responses during nodule development. Calcium spiking, kinases, PLC activity and possibly G proteins appear to be components downstream of the NFs perception pathway. Our results suggest the occurrence of a dual signaling pathway that could involve both G proteins and PLC in Phaseolus vulgaris during the development of root nodules.

Conventional and Novel Gγ Protein Families Constitute the Heterotrimeric G-Protein Signaling Network in Soybean

“…We analyzed the tissue specific expression of the three families of GmGγ genes in vegetative tissues and reproductive tissues. Additionally given the possible role of G-protein dependent signaling during nodulation [26] – [30] , we also analyzed the expression of GmGγ genes in this legume-specific tissue. Of the group I genes, GmGγ4 exhibits overall high expression compared with the other members of this group ( Figure 3A ).…”

Plant phospholipases D and C and their diverse functions in stress responses

“…Carrot PI-PLC was activated by wasp venom peptide mastoparan or the active analog Mas-7 [211] whereas neomycin (100 µM) inhibiting the uptake of Mas-7 suppressed the Mas-7 stimulation of PI-PLC activity [211]. PI-PLC activity was stimulated by mastoparan in rhizobia/legume symbiosis [212]. Type-III phosphatidylinositol 4-kinases (PI4Ks) are necessary for PI-PLC activation as they provide the substrates such as PI(4)P and PI(4,5)P 2 [213].…”

An elaborate heterotrimeric G‐protein family from soybean expands the diversity of plant G‐protein networks

“…For example, nodules show higher expression of GmGa1-3, but not GmGa4. This is interesting because multiple pharmacological experiments suggest the involvement of G-proteins in signaling processes related to nodulation (Pingret et al, 1998;den Hartog et al, 2001;Kelly & Irving, 2003;Charron et al, 2004;Sun et al, 2007;Santos-Briones et al, 2009).…”

“…Some examples include the G-proteinregulated blue and red light signaling pathways in pea (Warpeha et al, 1991), induction of root hair deformation in Vigna, and expression of nodulation-specific genes in Medicago by mastoparan, a known G-protein agonist (Kelly & Irving, 2003;Sun et al, 2007). Additionally, some wellestablished effectors of G-protein signaling, for example phospholipase C (PLC) and D (PLD) are involved in mastoparan-induced root hair deformation and development of root nodules (Pingret et al, 1998;den Hartog et al, 2001;Charron et al, 2004;Santos-Briones et al, 2009). G-proteins and PLC are also involved in an elicitor-induced oxidative burst in soybean cells (Legendre et al, 1992).…”