Genome reannotation and gland-specific transcriptome analysis identify new effector candidates in Meloidogyne chitwoodi

The root-knot nematode (RKN) Meloidogyne chitwoodi is a threat for potato production in the western United States (U.S.), negatively impacting potato yield and product value. Meloidogyne chitwoodi produce proteins, called effectors, in their esophageal glands that are secreted during parasitism and play integral roles in plant-nematode interactions. Because the esophageal glands are the main effector secretory organs, we isolated juvenile gland cells and performed gland transcriptome analysis with our newly improved genome annotation. The gland-specific transcriptome data gave us an enrichment of gland-localized genes, which was validated by in situ hybridization. The gland transcriptome analysis led to the identification of 125 effector candidates. One of the effectors that was highly expressed in the pre-parasitic J2 gland tissue, referred to as McGland26, was further characterized. Arabidopsis thaliana expressing McGland26 showed enhanced susceptibility to M. chitwoodi. However, the ectopic expression of McGland26 in planta did not suppress plant defenses, suggesting that this effector might be involved in processes other than interfering with plant immunity. Our data show that by using the gland transcriptome, a good quality genome annotation, and stringent selection criteria, we can increase the efficiency of effector identification, which can be used to develop more sustainable management tools.