Heterotrimeric Gα subunit from wheat (Triticum aestivum), GA3, interacts with the calcium-binding protein, Clo3, and the phosphoinositide-specific phospholipase C, PI-PLC1

Abstract

The canonical Gα subunit of the heterotrimeric G protein complex from wheat (Triticum aestivum), GA3, and the calcium-binding protein, Clo3, were revealed to interact both in vivo and in vitro and Clo3 was shown to enhance the GTPase activity of GA3. Clo3 is a member of the caleosin gene family in wheat with a single EF-hand domain and is induced during cold acclimation. Bimolecular Fluorescent Complementation (BiFC) was used to localize the interaction between Clo3 and GA3 to the plasma membrane (PM). Even though heterotrimeric G-protein signaling and Ca²⁺ signaling have both been shown to play a role in the response to environmental stresses in plants, little is known about the interaction between calcium-binding proteins and Gα. The GAP activity of Clo3 towards GA3 suggests it may play a role in the inactivation of GA3 as part of the stress response in plants. GA3 was also shown to interact with the phosphoinositide-specific phospholipase C, PI-PLC1, not only in the PM but also in the endoplasmic reticulum (ER). Surprisingly, Clo3 was also shown to interact with PI-PLC1 in the PM and ER. In vitro analysis of the protein-protein interaction showed that the interaction of Clo3 with GA3 and PI-PLC1 is enhanced by high Ca²⁺ levels. Three-way affinity characterizations with GA3, Clo3 and PI-PLC1 showed the interaction with Clo3 to be competitive, which suggests that Clo3 may play a role in the Ca²⁺-triggered feedback regulation of both GA3 and PI-PLC1. This hypothesis was further supported by the demonstration that Clo3 has GAP activity with GA3.

The Reductase Activity of the Arabidopsis Caleosin RESPONSIVE TO DESSICATION20 Mediates Gibberellin-Dependent Flowering Time, Abscisic Acid Sensitivity, and Tolerance to Oxidative Stress

“…This oxylipin was postulated to act as a second messenger in ROS signaling (op den Camp et al, 2003). A putative role of caleosin in ROS signaling is further supported by the recent report of the binding of a wheat (Triticum aestivum) RD20 homolog to G-proteins (Khalil et al, 2011) that are involved in signaling mediated by ROS (Joo et al, 2005). The inability of the rd20 mutant to enhance the production of 13-LOX-derived FAOHs rendered this mutant sensitive to Paraquat.…”

A Caleosin-Like Protein with Peroxygenase Activity Mediates Aspergillus flavus Development, Aflatoxin Accumulation, and Seed Infection

“…Likewise, deletion of one ␤ subunit of the heterotrimeric G-protein complex in A. flavus yielded an aconidial, aflatoxin-null phenotype for the resulting strain (66). Plant caleosin has been found to link to the G-protein component (68). Thus, at present, we cannot exclude the possibility that fungal caleosin and the oxylipins derived from it act by modulating the G-protein signaling pathway, resulting in an alteration of fungal development and, therefore, mycotoxin production.…”

Integral Proteins in Plant Oil Bodies

“…In Arabidopsis, a stress-responsive caleosin-like protein, AtCLO4, was demonstrated to act as a negative regulator of ABA responses [103], whereas another caleosin-like protein, RD20, was involved in ABA-mediated inhibition of germination but did not response to biotic or abiotic stresses [104]. Recently, a wheat caleosin-like protein was proposed to play a role in the Ca 2+ -triggered feedback regulation of both the canonical Gα subunit of the heterotrimeric G protein complex and phosphoinositidespecific phospholipase C [105], and a noncanonical caleosin from Arabidopsis was found to epoxidize unsaturated fatty acids efficiently with complete stereoselectivity [106]. Taken together, the recent research progress on the identification of caleosin functions is encouraging.…”