The Novel Secreted Meloidogyne incognita Effector MiISE6 Targets the Host Nucleus and Facilitates Parasitism in Arabidopsis.

Qianqian Shi,Zhenchuan Mao,Runmao Lin,Jian Ling,Bingyan Xie,Xi Zhang,Rui Liu,Yuhong Yang,Yunsheng Wang,Xiaoping Zhang,Xinyue Cheng

doi:10.3389/fpls.2018.00252

Abstract

Meloidogyne incognita is highly specialized parasite that interacts with host plants using a range of strategies. The effectors are synthesized in the esophageal glands and secreted into plant cells through a needle-like stylet during parasitism. In this study, based on RNA-seq and bioinformatics analysis, we predicted 110 putative Meloidogyne incognita effectors that contain nuclear localization signals (NLSs). Combining the Burkholderia glumae–pEDV based screening system with subcellular localization, from 20 randomly selected NLS effector candidates, we identified an effector MiISE6 that can effectively suppress B. glumae-induced cell death in Nicotiana benthamiana, targets to the nuclei of plant cells, and is highly expressed in early parasitic J2 stage. Sequence analysis showed that MiISE6 is a 157-amino acid peptide, with an OGFr_N domain and two NLS motifs. Hybridization in situ verified that MiISE6 is expressed in the subventral esophageal glands. Yeast invertase secretion assay validated the function of the signal peptide harbored in MiISE6. Transgenic Arabidopsis thaliana plants expressing MiISE6 become more susceptible to M. incognita. Inversely, the host-derived RNAi of MiISE6 of the nematode can decrease its parasitism on host. Based on transcriptome analysis of the MiISE6 transgenic Arabidopsis samples and the wild-type samples, we obtained 852 differentially expressed genes (DEGs). Integrating Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, we found that expression of MiISE6 in Arabidopsis can suppress jasmonate signaling pathway. In addition, the expression of genes related to cell wall modification and the ubiquitination proteasome pathway also have detectable changes in the transgenic plants. Results from the present study suggest that MiISE6 is involved in interaction between nematode-plant, and plays an important role during the early stages of parasitism by interfering multiple signaling pathways of plant. Moreover, we found homologs of MiISE6 in other sedentary nematodes, Meloidogyne hapla and Globodera pallida. Our experimental results provide evidence to decipher the molecular mechanisms underlying the manipulation of host immune defense responses by plant parasitic nematodes, and transcriptome data also provide useful information for further study nematode–plant interactions.

Highlights

Meloidogyne incognita, the southern root knot nematode (RKN), is an economically important, sedentary nematode that infests roots of a wide range of crop plants (Alioto et al, 2015)
By a series bioinformatic analysis, such as searching out the sequences with signal peptides and discarding the sequences with putative transmembrane-spanning regions, analyzing subcellular location and removing proteins located in mitochondria, nuclear localization signals (NLSs) motif predicting, totally 110 potential NLS effectors are predicted from M. incognita, and they are taken as candidate effectors with putative immune function for further analysis
The expression pattern of MiISE6 is similar to other published nematode effectors which play central roles in nematode parasitism (Chronis et al, 2013; Lin et al, 2016; Chen et al, 2017), so we focus on MiISE6 and speculate it may play an important role during the initial establishment of the plantnematode interaction

Summary

Introduction

Meloidogyne incognita, the southern root knot nematode (RKN), is an economically important, sedentary nematode that infests roots of a wide range of crop plants (Alioto et al, 2015). The formation of GCs are mediated through secretions (referred to as effectors) from the esophageal gland (dorsal and subventral) that are injected into root cells via the stylet, resulting in physiological and morphological changes in root cells (Abad et al, 2003). The esophageal glands of M. incognita are composed of two subventral gland (SvG) cells and one dorsal gland cell. The SvG cells are active in the pre-parasitic and parasitic stages, producing effectors required for root invasion. The dorsal gland cell is active during the sedentary stages, synthesizing proteins involved in feeding site development and maintenance (Davis et al, 2000). Once secreted from esophageal glands into root cells, effectors may be localized to different cellular compartments where they may assume diverse cellular functions to increase parasitism. The manipulation of host cellular functions, such as host transcription, chromatin remodeling, and immune responses, involves targeting of the host nucleus by secreted effectors (Quentin et al, 2013)

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Conclusion