Isolation and characterization of a fatty acid- and retinoid-binding protein from the cereal cyst nematode Heterodera avenae

A gene encoding fatty acid- and retinoid-binding protein was isolated from the cereal cyst nematode Heterodera avenae and the biochemical function of the protein that it encodes was analysed. The full-length cDNA of the Ha-far-1 gene is 827 bp long and includes a 22- nucleotide trans-spliced leader sequence (SL1) at its 5-end. The genomic clone of Ha-far-1 consists of eight exons separated by seven introns, which range in size from 48 to 186 bp. The Ha-far-1 cDNA contains an open reading frame encoding a 191 amino acid protein, with a predicted secretory signal peptide. Sequence analysis showed that Ha-FAR-1 has highest similarity to the Gp-FAR-1 protein from the potato cyst nematode, Globodera pallida and that the protein was grouped with all homologues from other plant-parasitic nematodes in a phylogenetic analysis. Fluorescence-based ligand binding analysis confirmed that the recombinant Ha-FAR-1 protein was able to bind fatty acids and retinol. Spatial and temporal expression assays showed that the transcripts of Ha-far-1 accumulated mainly in the hypodermis and that the gene is most highly expressed in third-stage juveniles of H. avenae. Fluorescence immunolocalization showed that the Ha-FAR-1 protein was present on the surface of the infective second-stage juveniles of H. avenae. Nematodes treated with dsRNA corresponding to Ha-far-1 showed significantly reduced reproduction compared to nematodes exposed to dsRNA from a non-endogenous gene, suggesting that Ha-far-1 may be an effective target gene for control of H. avenae using an RNAi strategy.