25002:

A new gene from soybean with similarity to G-protein-coupled receptors.

Authors:	Dammann, Christian(A)Bhattacharyya, Madan, K.(A)
Affiliations:	(A): Plant Biology Division, Noble Foundation
Presenter:	Dammann, Christian , cdammann@noble.org

In recent years several phosphoinositide-specific phospholipase C (PI-PLC) genes have been cloned from different plant species. Interestingly, all genes found so far show the highest similarity to mammalian PI-PLC-d isoforms. This class of PI-PLCs interacts in mammalian cells with a1-adrenergic receptors and is activated by G-proteins. Recent data show the involvement of PI-PLC signaling in response to fungal elicitors, abscisic acid-induced stomatal closure, Nod factor-induced gene expression and leaf movement by light in Samanea saman. It has also been reported that PI-PLC activity can be induced by nutrients and osmotic shock. How the regulation of PI-PLC is achieved in plants is not known. However, there is evidence suggesting that G-proteins are involved in the regulation of plant PI-PLC. For example, mastoparan, a G-protein-activating peptide, has been shown to induce PI-PLC activity. In an attempt to elucidate the regulation of PI-PLC in plants we employed the yeast two hybrid system. Using soybean PI-PLC1 as the bait we have identified a protein that binds to this isoform. A full-length cDNA encoding a protein of 878 amino acids has been isolated. PLAP (PLC Associated Protein) contains three putative transmembrane domains. Homologous genes are present in Arabidopsis and rice. No significant homology to genes with known function could be found in the GenBank. However, a search in the "prints" database revealed six footprints of the rhodopsin superfamily of G-protein-coupled receptors. Three footprints map in the predicted transmembrane domains of this new protein. Interestingly, a1-adrenergic receptors belong also to this superfamily. Whether PLAP is indeed a receptor or has other functions remains to be shown. We are currently performing in vitro PI-PLC binding and activation assays to characterize this novel gene. Southern blot analysis indicates that there are two PLAP copies in the soybean genome. The gene is constitutively expressed in all soybean organs with very little variation in the expression level. Moreover, almost identical amounts of transcript were detected in developing and mature tissues from leaves, flowers and fruits. Nevertheless, preliminary results indicate that PI-PLC activity itself can effect the transcription of PLAP. This suggests the presence of a regulatory feedback mechanism that ensures the stable level of PI-PLC activity that is found in cells.