Discovery of Novel Effector Protein Candidates Produced in the Dorsal Gland of Adult Female Root-Knot Nematodes

Root-knot nematodes (RKN) (Meloidogyne spp.) represent one of the most damaging groups of plant-parasitic nematodes. They secrete effector proteins through a protrusible stylet to manipulate host cells for their benefit. Stylet-secreted effector proteins are produced within specialized secretory esophageal gland cells, one dorsal gland (DG) and two subventral glands (SvG), whose activity differ throughout the nematode life cycle. Previous gland transcriptomic profiling studies identified dozens of candidate RKN effectors but were focused on the juvenile stages of the nematode, when the SvGs are most active. We developed a new approach to enrich for the active DGs of M. incognita adult female RKNfor RNA and protein extraction. Female heads weremanually cut fromthe body, and a combination of sonication and vortexing was used to dislodge contents inside the heads. DG-enriched fractions were collected by filtering, using cell strainers. Comparative transcriptome profiling of pre-parasitic second-stage juveniles, female heads, and DGenriched samples was conducted using RNA sequencing. Application of an established effector mining pipeline led to the identification of 83 candidate effector genes upregulated in DGenriched samples of adult females that code for proteins with a predicted signal peptide but lack transmembrane domains or homology to proteins in the free-living nematode Caenorhabditis elegans. In situ hybridization resulted in the identification of 14 new DG-specific candidate effectors expressed in adult females. Taken together, we have identified novel candidate Meloidogyne effector genes that may have essential roles during later stages of parasitism.

Automated summary

Root-knot nematodes secrete effector proteins to manipulate host cells. A study identified 83 candidate effector genes that are upregulated in adult females. These findings provide insights into the parasitic role of root-knot nematodes.