Abstract
Cereal cyst nematodes are sedentary biotrophic endoparasites that maintain a complex interaction with their host plants. Nematode effector proteins are synthesized in the oesophageal glands and are secreted into plant tissues through the stylet. To understand the function of nematode effectors in parasitic plants, we cloned predicted effectors genes from Heterodera avenae and transiently expressed them in Nicotiana benthamiana. Infiltration assays showed that HaEXPB2, a predicted expansin-like protein, caused cell death in N. benthamiana. In situ hybridization showed that HaEXPB2 transcripts were localised within the subventral gland cells of the pre-parasitic second-stage nematode. HaEXPB2 had the highest expression levels in parasitic second-stage juveniles. Subcellular localization assays revealed that HaEXPB2 could be localized in the plant cell wall after H. avenae infection.This The cell wall localization was likely affected by its N-terminal and C-terminal regions. In addition, we found that HaEXPB2 bound to cellulose and its carbohydrate-binding domain was required for this binding. The infectivity of H. avenae was significantly reduced when HaEXPB2 was knocked down by RNA interference in vitro. This study indicates that HaEXPB2 may play an important role in the parasitism of H. avenae through targeting the host cell wall.
Highlights
The cereal cyst nematode Heterodera avenae causes severe losses to cereal crops across the world
H. avenae revealed a total of 39 sequences; 27 of them were similar to previously identified effectors from other plant-parasitic nematodes, and 12 of them were identified as novel effectors containing predicted N-terminal signal peptides (SP) and lacking a transmembrane helix (Supplementary Table 1)
All the candidate effectors were screened by transient expression assay in N. benthamiana leaves in order to identify candidates that induced cell death
Summary
The cereal cyst nematode Heterodera avenae causes severe losses to cereal crops across the world. The rapid advances in sequencing technology have provided tools for studying genetic resources from which candidate effector genes have been identified from a wide range of plant-parasitic nematodes. These resources include transcriptome sequences from cyst nematodes such as H. schachtii, and H. glycines[18,19]. Nematodes produce a range of cell wall modifying proteins that help overcome this barrier during parasitism including pectate lyase, expansin, β- 1,4-endoglucanase and polygalacturonase. The β-1,4-endoglucanases, the first cell wall-degrading enzymes identified from plant-parasitic cyst nematodes, belong to glycosylhydrolase family 5 (GHF5)[26,27,28,29]. A cellulose-binding protein (CBP) isolated from H. schachtii interacts directly with Arabidopsis pectin methylesterase protein 3 (PME3), activating and potentially targeting this enzyme to aid H. schachtii parasitism[35]
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