Clg2p interacts with Clf and ClUrase to regulate appressorium formation, pathogenicity and conidial morphology in Curvularia lunata.

Tong Liu,Yuhu Zuo,Youli Zhang,Jumei Hou,Yuying Wang,Bingchen Ma,Yazhong Jin,Xiwang Ke,Lianmei Tai,Kishore Dey

doi:10.1038/srep24047

Abstract

Ras is a small GTPase that regulates numerous processes in the cellular development and morphogenesis of many organisms. In this study, we identified and functionally characterized the Clg2p gene of Curvularia lunata, which is homologous with the Ras protein. The Clg2p deletion mutant (ΔClg2p) had altered appressorium formation and conidial morphology and produced fewer, smaller lesions compared with the wild-type strain. When a dominant Clg2p allele was introduced into the mutant, all of these defective phenotypes were completely restored. To further understand the regulation of Clg2p in appressorium formation and conidial morphology, and its role in pathogenicity, seven Clg2p-interacting proteins were screened using a yeast two-hybrid assay. Two of these proteins, Clf, a homologue of Mst11, which corresponds to MAP kinase kinase kinase in Magnaporthe oryzae, and urate oxidase (designated ClUrase) were functionally characterized. Clg2p specifically interacted with Clf through its RA domain to regulate appressorium formation and pathogenicity, whereas the Clg2p-ClUrase interaction regulated conidial morphology without affecting fungal pathogenicity. This report is the first to elucidate the regulatory mechanism of the key Ras protein Clg2p in C. lunata.

Highlights

The interplay of signals between the host and pathogenic fungi is believed to be mediated by Ca2+, cyclic adenosine monophosphate and mitogen-activated protein kinase (MAPK)[19,20,21]
The expression was highest in 3 h germinating conidia, indicating that the expression of Clg2p correlates with the pathogen infection, growth and appressorium development (Fig. 1D)
Our results suggest that, in C. lunata, the interaction of Clg2p with Clf occurs via its RA domain, and this interaction is involved in appressorium formation, morphological development and pathogenicity

Summary

Introduction

The interplay of signals between the host and pathogenic fungi is believed to be mediated by Ca2+, cyclic adenosine monophosphate (cAMP) and mitogen-activated protein kinase (MAPK)[19,20,21]. We created a normalized, full-length cDNA library of C. lunata and annotated a number of expressed sequence tag (EST) sequences using bioinformatics[27] Among these ESTs, we identified a Ras homologue (designated Clg2p) from C. lunata and investigated its biological and regulatory role during infection. Ras proteins affect cellular signal transduction pathways with important regulatory roles in morphogenesis, conidiation, appressorium development and pathogenicity in fungi[35,36,37,38]. The results presented in this study show that the Clg2p protein interacts with Clf and ClUrase, the urate oxidase protein, to regulate appressorium development and conidial morphology This interaction is required for full pathogenicity in C. lunata. These results provide new insights into the signal transduction mechanism during the infection process of C. lunata and may lead to optimal target sites for chemical control of this devastating pathogen

Methods

Results

Conclusion