HaCRT1 of Heterodera avenae Is Required for the Pathogenicity of the Cereal Cyst Nematode.

Jing Liu,Liangying Dai,Maoyan Liu,Wenkun Huang,Deliang Peng,Wen Su,Huan Peng

doi:10.3389/fpls.2020.583584

Abstract

Cereal cyst nematodes are sedentary biotrophic endoparasites that secrete effector proteins into plant tissues to transit normal cells into specialized feeding sites and suppress plant defenses. To understand the function of nematode effectors in Heterodera avenae, here, we identified a calreticulin protein HaCRT1, which could suppress the cell death induced by Bax when expressed in Nicotiana benthamiana. HaCRT1 is synthetized in the subventral gland cells of pre-parasitic second-stage nematodes. Real-time PCR assays indicated that the expression of HaCRT1 was highest in parasitic second-stage juveniles. The expression of an HaCRT1-RFP fusion in N. benthamiana revealed that it was localized in the endoplasmic reticulum of the plant cell. The ability of H. avenae infecting plants was significantly reduced when HaCRT1 was knocked down by RNA interference in vitro. Arabidopsis thaliana plants expressing HaCRT1 were more susceptible than wild-type plants to Pseudomonas syringae. The induction of defense-related genes, PAD4, WRKY33, FRK1, and WRKY29, after treatment with flg22 was suppressed in HaCRT1-transgenic plants. Also, the ROS accumulation induced by flg22 was reduced in the HaCRT1-transgenic plants compared to wild-type plants. HaCRT1 overexpression increased the cytosolic Ca2+ concentration in A. thaliana. These data suggested that HaCRT1 may contribute to the pathogenicity of H. avenae by suppressing host basal defense.

Highlights

The cereal cyst nematode (CCN, Heterodera avenae), belonging to the genus Heterodera, is one of the most economically damaging plant-parasitic nematodes worldwide (Bonfil et al, 2004; Nicol et al, 2007)
Mi-CRT is synthesized in the esophageal glands and secreted by the stylet into the apoplasm of host plant tissues and plays an important role during the interaction by suppressing plant basal defenses (Jaubert et al, 2005; Jaouannet et al, 2013)
We analyzed the calreticulin HaCRT1 from the cyst nematode H. avenae and demonstrated that its role is similar to Mi-CRT in plantdefense suppression

Summary

Introduction

The cereal cyst nematode (CCN, Heterodera avenae), belonging to the genus Heterodera, is one of the most economically damaging plant-parasitic nematodes worldwide (Bonfil et al, 2004; Nicol et al, 2007). The success of parasitism relies on its capability to establish the feeding site syncytium and break through the barrier of host immunity. Secreting proteins into host plant tissues is a major event in the plant– nematode interaction (Bellafiore and Briggs, 2010). These secreted proteins, known as effectors, are synthetized in the nematode’s two subventral and one dorsal gland cells, and HaCRT1 Is Required for the Pathogenicity are secreted into the host plant tissues through the stylet, a typical hollow needle-like structure (Mitchum et al, 2013). Nematode effectors transform plant cells into specialized feeding sites and counteract plant defenses by modifying cell walls, interfering with signaling, and regulating epigenetics (Hassan et al, 2010; Gheysen and Mitchum, 2011; Hewezi and Baum, 2013)

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