A root‐knot nematode small glycine and cysteine‐rich secreted effector, MiSGCR1, is involved in plant parasitism

Abstract

Root-knot nematodes, Meloidogyne spp., are obligate endoparasites that maintain a biotrophic relationship with their hosts. They infect roots as microscopic vermiform second-stage juveniles, and establish specialized feeding structures called 'giant-cells', from which they withdraw water and nutrients. The nematode effector proteins secreted in planta are key elements in the molecular dialogue of parasitism. Here, we compared Illumina RNA-seq transcriptomes for M. incognita obtained at various points in the lifecycle, and identified 31 genes more strongly expressed in parasitic stages than in preparasitic juveniles. We then selected candidate effectors for functional characterization. Quantitative real-time PCR and in situ hybridizations showed that the validated differentially expressed genes are predominantly specifically expressed in oesophageal glands of the nematode. We also soaked the nematodes in siRNA to silence these genes and to determine their role in pathogenicity. The silencing of the dorsal gland specific-Minc18876 and its paralogues resulted in a significant, reproducible decrease in the number of mature females with egg masses, demonstrating a potentially important role for the small glycine- and cysteine-rich effector MiSGCR1 in early stages of plant-nematode interaction. Finally, we report that MiSGCR1 suppresses plant cell death induced by bacterial or oomycete triggers of plant defense.

Gene copy number variations as signatures of adaptive evolution in the parthenogenetic, plant‐parasitic nematode Meloidogyne incognita

“…In addition, the comparison of the 184 genes exhibiting CNVs to > 100 characterized M. incognita putative effectors (Nguyen et al., ) revealed three positive matches: a metallopeptidase (Minc00108), a gene of unknown function expressed in the subventral glands (Minc13292) and a gene of unknown function expressed in the amphids (Minc00158).…”

“…We considered the GO terms that returned a FDR threshold < 0.05 as significantly enriched. To further characterize these genes, we compared them to a list of > 100 M. incognita putative effectors (i.e., genes encoding secreted proteins that mediate interactions with the host), as recently reviewed in Nguyen et al (2018).…”

The Meloidogyne graminicola effector Mg16820 is secreted in the apoplast and cytoplasm to suppress plant host defense responses

“…In addition, Msp40 was able to suppress callose deposition and the expression of genes related to the elf18‐triggered PTI immune response. Like Mg16820, Msp40 was able to suppress both PTI and multiple ETI pathways (Niu et al, ). However, in contrast with Mg16820, the different activities of Msp40 appeared in the same cell compartment, the nucleus and cytoplasm, whereas Mg16820 works in the apoplast as well as in the cytoplasm.…”

Attempt to Silence Genes of the RNAi Pathways of the Root-Knot Nematode, Meloidogyne incognita Results in Diverse Responses Including Increase and No Change in Expression of Some Genes

“…A survey of current literature and reviews appears to suggest that almost all genes of PPNs are susceptible to RNAi and that once the appropriate stage of a PPN is treated with dsRNA, there is a guarantee of a measurable gene knockdown and a subsequent negative effect or disruption on the biology of the nematode or its ability to successfully interact with its host. To date, few PPN genes have been reported to be somewhat refractory to RNAi where responses to similar amounts of dsRNA that trigger silencing of other genes under similar conditions include no measurable reduction in transcript abundance, a considerable delay in gene knockdown effect after exposure to dsRNA, a relatively quick recovery of transcript to levels before exposure to dsRNA triggers and no obvious deleterious effect of silencing on the behavior and biology of the target nematode (Bakhetia et al, 2008;Dalzell et al, 2010aDalzell et al, , 2011Danchin et al, 2013;Chi et al, 2016;Shivakumara et al, 2016;Nguyen et al, 2018). PPN genes currently reported as refractory to exogenous RNAi have diverse roles in cellular processes and include nematode effectors and the cytosolic RNase III enzyme dicer of M. incognita.…”

“…PPN genes currently reported as refractory to exogenous RNAi have diverse roles in cellular processes and include nematode effectors and the cytosolic RNase III enzyme dicer of M. incognita. Among the many reasons suggested for RNAi recalcitrance are the nature, function, and expression turnover of target genes Danchin et al, 2013;Tan et al, 2013;Chi et al, 2016;Shivakumara et al, 2016;Nguyen et al, 2018).…”