G-protein-coupled signaling in Arabidopsis.

With an essentially complete plant genome in hand, it is now possible to conclude that a single or possibly just two canonical heterotrimeric G-protein complexes are present in Arabidopsis. In stark contrast, more than one hundred such complexes are found in some metazoans. Nonetheless, it appears that heterotrimeric G-protein complexes couple or affect many different signaling pathways in plants. In addition, there are very few, if any, candidate G-protein-coupled receptors through which this single complex can couple to downstream effectors. Furthermore, some of the classical downstream effectors that are activated by heterotrimeric G proteins in metazoans are also lacking in plants. Thus, we are left with the urgent challenge to determine the novel mechanism of G-protein signaling in plant cells. Recent advances using reverse and molecular genetic approaches have re-opened this topic for plant biologists and the resulting tools will accelerate our progress.