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Molecular characterization of the reniform nematode C-type lectin gene family reveals a likely role in mitigating environmental stresses during plant parasitism

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The reniform nematode, Rotylenchulus reniformis, is a damaging semi-endoparasitic pathogen of more than 300 plant species. Transcriptome sequencing of R. reniformis parasitic females revealed an enrichment for sequences homologous to C-type lectins (CTLs), an evolutionarily ancient family of Ca+2-dependent carbohydrate-binding proteins that are involved in the innate immune response. To gain further insight as to the potential role of CTLs in facilitating plant parasitism by R. reniformis, we performed a comprehensive assessment of the CTL gene family. 5′- and 3′-RACE experiments identified a total of 11 R. reniformis CTL transcripts (Rr-ctl-1 through Rr-ctl-11) that ranged in length from1083 to 1194 bp and showed 93–99% identity with one another. An alignment of cDNA and genomic sequences revealed three introns with the first intron residing within the 5′-untranslated region. BLAST analyses showed the closest homologs belonging to the parasitic nematodes Heligmosomoides polygyrus and Heterodera glycines. Rr-ctl-1, -2, and -3 were expressed throughout the R. reniformis life cycle; whereas, the remaining Rr-ctl genes showed life stage-specific expression. Quantitative real time RT-PCR determined that Rr-ctl transcripts were 839-fold higher in sedentary female nematodes than the next most abundant life stage. Predicted Rr-CTL peptides ranged from 301 to 338 amino acids long, possessed an N-terminal signal peptide for secretion, and contained a conserved CLECT domain, including the mannose-binding motifs EPN and EPD and the conserved WND motif that is required for binding Ca+2. In addition, Rr-CTL peptides harbored repeats of a novel 17-mer motif within their C-terminus that showed similarity to motifs associated with bacterial ice nucleation proteins. In situ hybridization of Rr-ctl transcripts within sedentary females showed specific accumulation within the hypodermis of the body regions exposed to the soil environment; those structures embedded within the root during parasitism did not show Rr-ctl expression. A phylogenetic analysis of the Rr-CTL CLECT domain with homologous domains from other nematode species suggested that CTLs from animal- and plant parasitic genera may have evolved in order to play an active role in the parasitic process.
Satish Ganji , Johnie N. Jenkins , Martin J. Wubben
Heligmosomoides polygyrus , Heterodera glycines , Rotylenchulus reniformis , binding proteins , body regions , complementary DNA , edaphic factors , females , genes , ice nucleation , immunity , in situ hybridization , introns , lectins , messenger RNA , parasitism , peptides , phylogeny , reverse transcriptase polymerase chain reaction , sequence homology , signal peptide , transcriptome
USDA Scientist Submission
Gene 2014 3 10 v.537
Journal Articles, USDA Authors, Peer-Reviewed
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