Abstract
The rice root-knot nematode, Meloidogyne graminicola, is a serious pest in most rice-growing countries. Usually, nematodes employ antioxidants to counteract the harm of reactive oxygen species (ROS) and facilitate their infection. Here the gene encoding M. graminicola protein disulphide isomerase (MgPDI) was identified. The deduced protein is highly conserved in the putative active-site Cys-Gly-His-Cys. In situ hybridization showed that MgPDI was specifically localized within esophageal glands of pre-parasitic second stage juveniles (J2s). MgPDI was significantly up-regulated in the late parasitic J2s. Characterization of the recombinant protein showed that the purified MgPDI exhibited similar activities to other oxidases/isomerases such as the refolding of the scrambled RNase and insulin disulfide reductase and the protection of plasmid DNA and living cells from ROS damage. In addition, silencing of MgPDI by RNA interference in the pre-parasitic J2s lowered their multiplication factor. MgPDI expression was up-regulated in the presence of exogenous H2O2, whereas MgPDI silencing resulted in an increase in mortality under H2O2 stress. MgPDI is localized in the apoplast when transient expression in Nicotiana benthamiana leaves. The results indicated that MgPDI plays important roles in the reproduction and pathogenicity of M. graminicola and it also contributes to protecting nematodes from exogenous H2O2 stress.
Highlights
Rice (Oryza sativa) is an important cereal crop; more than half of the world population relies on rice
Results of a BLASTP search showed that M. graminicola protein disulphide isomerase (MgPDI) shared 79%, 71%, 69%, 32% and 33% identity to protein disulphide isomerase (PDI) from Heterodera schachtii, Caenorhabditis elegans [NP_491995], Ascaris suum [ERG84937], Leishmania major [AAN75008], and Brugia malayi [XP_001899304], respectively
The present study identifies MgPDI encoding a typical PDI in the endoparasitic nematode M. graminicola, and MgPDI contains a 20-amino acid signal peptide at its N-terminal and two catalytic thioredoxin-like domains, each containing the canonical CGHC motif, and two non-catalytic domains (Fig. 1a,b)
Summary
Rice (Oryza sativa) is an important cereal crop; more than half of the world population relies on rice. Protein disulphide isomerase includes two catalytically active thioredoxin domains containing characteristic Cys-Gly-His-Cys (CGHC) active-site motifs, www.nature.com/scientificreports/. Other studies have reported that PDIs of pathogens play important roles in virulence when infecting a host[15]. A 56-kDa protein designated MgPDI that contains a CGHC active motif in the rice root-knot nematode, M. graminicola, was identified and characterized. It is localized in the apoplast when transient expression in N. benthamiana leaves. MgPDI likely plays an important role in protecting M. graminicola against rice-released ROS and facilitating M. graminicola infestation of rice hosts and its role was demonstrated in this study
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