Ternary WD40 Repeat-Containing Protein Complexes: Evolution, Composition and Roles in Plant Immunity.

Jimi C Miller,Nicole K Clay,William R Chezem

doi:10.3389/fpls.2015.01108

Abstract

Plants, like mammals, rely on their innate immune system to perceive and discriminate among the majority of their microbial pathogens. Unlike mammals, plants respond to this molecular dialog by unleashing a complex chemical arsenal of defense metabolites to resist or evade pathogen infection. In basal or non-host resistance, plants utilize signal transduction pathways to detect “non-self,” “damaged-self,” and “altered-self”- associated molecular patterns and translate these “danger” signals into largely inducible chemical defenses. The WD40 repeat (WDR)-containing proteins Gβ and TTG1 are constituents of two independent ternary protein complexes functioning at opposite ends of a plant immune signaling pathway. They are also encoded by single-copy genes that are ubiquitous in higher plants, implying the limited diversity and functional conservation of their respective complexes. In this review, we summarize what is currently known about the evolutionary history of these WDR-containing ternary complexes, their repertoire and combinatorial interactions, and their downstream effectors and pathways in plant defense.

Highlights

WD40 repeat (WDR)-containing proteins are prevalent in eukaryotes, but rarely present in prokaryotes (Janda et al, 1996; Stirnimann et al, 2010)
HsGNB1 remains the sole Gβ with a solved crystal structure, which serves as the foundation for the predicted Gβ structures generated by structural bioinformatics
Plants have several families of non-canonical G-protein-coupled receptors (GPCRs)-like sequences, three of which (GCR1, GTG1, and GTG2) have been shown to interact in planta with the Arabidopsis canonical Gα GPA1 and modulate an ABA-mediated drought response (Pandey and Assmann, 2004; Pandey et al, 2009). It remains controversial whether the GPCR-like proteins are bona fide GPCRs, a recent structural bioinformatics study has found GCR1 to be a strong GPCR candidate based on its predicted heptahelical scaffold and GPCR fold (Taddese et al, 2014)

Summary

INTRODUCTION

WD40 repeat (WDR)-containing proteins are prevalent in eukaryotes, but rarely present in prokaryotes (Janda et al, 1996; Stirnimann et al, 2010). HsGNB1 remains the sole Gβ with a solved crystal structure, which serves as the foundation (along with a handful of solved RACK1 structures) for the predicted Gβ structures generated by structural bioinformatics Within these confines, there is some evidence that the Gβ-specific structure mediating the Gβγ interaction may not be conserved across eukaryotes. Plants have several families of non-canonical GPCR-like sequences, three of which (GCR1, GTG1, and GTG2) have been shown to interact in planta with the Arabidopsis canonical Gα GPA1 and modulate an ABA-mediated drought response (Pandey and Assmann, 2004; Pandey et al, 2009) It remains controversial whether the GPCR-like proteins are bona fide GPCRs, a recent structural bioinformatics study has found GCR1 to be a strong GPCR candidate based on its predicted heptahelical scaffold and GPCR fold (Taddese et al, 2014). Despite the diversity of MAPK cascade scaffolds between plants and animals, the use of scaffolding proteins in signal transduction pathways appears universal

Evolutionary History of the Plant Gαβγ

Flavonoids in Defense

CONCLUSION