Abstract
BackgroundRoot-knot nematodes transform vascular host cells into permanent feeding structures to withdraw nutrients from the host plant. Ecotypes of Arabidopsis thaliana can display large quantitative variation in susceptibility to the root-knot nematode Meloidogyne incognita, which is thought to be independent of dominant major resistance genes. However, in an earlier genome-wide association study of the interaction between Arabidopsis and M. incognita we identified a quantitative trait locus harboring homologs of dominant resistance genes but with minor effect on susceptibility to the M. incognita population tested.ResultsHere, we report on the characterization of two of these genes encoding the TIR-NB-LRR immune receptor DSC1 (DOMINANT SUPPRESSOR OF Camta 3 NUMBER 1) and the TIR-NB-LRR-WRKY-MAPx protein WRKY19 in nematode-infected Arabidopsis roots. Nematode infection studies and whole transcriptome analyses using the Arabidopsis mutants showed that DSC1 and WRKY19 co-regulate susceptibility of Arabidopsis to M. incognita.ConclusionGiven the head-to-head orientation of DSC1 and WRKY19 in the Arabidopsis genome our data suggests that both genes may function as a TIR-NB-LRR immune receptor pair. Unlike other TIR-NB-LRR pairs involved in dominant disease resistance in plants, DSC1 and WRKY19 most likely regulate basal levels of immunity to root-knot nematodes.
Highlights
Root-knot nematodes transform vascular host cells into permanent feeding structures to withdraw nutrients from the host plant
Multiple Toll-interleukin-1 receptor (TIR)-nucleotide-binding site leucinerich repeat (NB-leucine-rich repeat (LRR)) protein encoding genes in a Quantitative Trait Locus (QTL) for susceptibility In our previously published Genome-wide association (GWA) study of the susceptibility of Arabidopsis to M. incognita we identified a single nucleotide polymorphism (SNP) marker on chromosome 4, which was closely linked to two genes with similarity to TIR-Nucleotide-binding site (NB)-LRR-type immune receptors [26]
BILE ACID TRANSPORTER 5 (BAT5), DOMINANT SUPPRESSOR of Camta3 NUMBER 1 (DSC1) and WRKY19 are all within 10 kb of SNP marker 138,442 and could be causal for the effect on susceptibility to M. incognita associated with this marker
Summary
Root-knot nematodes transform vascular host cells into permanent feeding structures to withdraw nutrients from the host plant. Ecotypes of Arabidopsis thaliana can display large quantitative variation in susceptibility to the root-knot nematode Meloidogyne incognita, which is thought to be independent of dominant major resistance genes. Infective second stage juveniles (J2) of M. incognita penetrate their host at the root elongation zone Thereafter, they migrate through the cortex to the root tip and enter the vascular cylinder via the columella and quiescence center. Plant cells carry surface-localized receptors to detect molecular patterns in the apoplast that are uniquely associated with host invasion by endoparasitic nematodes [4, 7, 8]. Arabidopsis mutant analyses (including BRASSINOSTEROID INSENSITIVE 1 (BRI1)-associated receptor kinase 1 (BAK1)) have shown that receptor-mediated basal immunity plays a significant role in the susceptibility of plants to root-knot nematodes [10]. Rootknot nematodes have effectors capable of selectively suppressing responses activated by surface-localized immune receptors, which indicates adaptation to this line of defense [11,12,13,14]
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