Recent studies have reported that plant-parasitic nematodes facilitate their infection by suppressing plant immunity via effectors, but the inhibitory mechanisms remain poorly understood. This study found that a novel effector MgMO289 is exclusively expressed in the dorsal esophageal gland of Meloidogyne graminicola and is up-regulated at parasitic third-/fourth-stage juveniles. In planta silencing of MgMO289 substantially increased plant resistance to M. graminicola. Further studies found that MgMO289 interacts with a new rice Cu metallochaperone OsHPP04, and the rice cCu/Zn-SOD2 is the target of OsHPP04. OsHPP04- and MgMO289-transgenic rice both exhibited an increased susceptibility to M. graminicola and a higher Cu/Zn-SOD activity, but lower O2 •− content, when compared to wild-type rice. Meanwhile, immune assays showed that MgMO289 can suppress host innate immunity. These findings reveal a novel pathway for a plant pathogen effector that utilize the host O2 •−-scavenging system to eliminate O2 •− and suppress plant immunity.

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Summary The use of Arabidopsis thaliana as a model plant increased the rate of molecular discoveries of plant-pathogen interactions. Although Meloidogyne graminicola has a relatively broad host range, it is not known whether it can infect A. thaliana. In this study, we showed that M. graminicola is able to invade A. thaliana and complete its life cycle 12-14 days after invasion. No significant difference in the total number of nematodes inside roots of A. thaliana and rice, Oryza sativa, was found at 14 day after inoculation (dai). Significantly more galls were formed in A. thaliana roots compared to the numbers in O. sativa roots at 14 dai. Females laid egg masses on the A. thaliana root surface and a large number of hatched juveniles of the next generation were obtained from infected A. thaliana roots. In addition, the infection of M. graminicola can induce expression of A. thaliana basal defence genes, such as AtMYB51, AtWRKY11, AtPR1 and AtFRK1, at 24 h after inoculation. Therefore, A. thaliana can be considered as a suitable host to study host-M. graminicola interactions and to understand the molecular mechanisms developed by M. graminicola to infect its dicotyledonous host plants. In addition, our results also showed that a delayed development of M. graminicola occurred in A. thaliana compared to O. sativa, and a higher proportion of empty galls appeared in A. thaliana roots than in O. sativa roots, suggesting A. thaliana is a less optimal host than rice.

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The complete mitochondrial genome (mitogenome) of Aphelenchoides besseyi is 16216 bp in size and has the typical organisation of nematode mitogenomes of Chromadorea, including 12 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes and the AT-rich non-coding region. The nucleotide composition of the mitogenome of A. besseyi is AT-biased (80.0%) and the AT skew is -0.289. The most common start codon for A. besseyi is ATT. The nad3 and nad4L genes have an incomplete stop codon consisting of just a T and the other PCGs stop with the full stop codons. All the tRNA genes display a non-typical cloverleaf structure of mitochondrial tRNA. The AT-rich non-coding region contains ten tandem repeat units with four different regions. Phylogenetic analysis based on concatenated amino acid sequences of 12 protein-coding genes showed that three Tylenchomorpha species, including A. besseyi, Bursaphelenchus mucronatus and B. xylophilus from the superfamily Aphelenchoidea, are placed within a well-supported monophyletic clade, but far from the other six Tylenchomorpha species Meloidogyne chitwoodi, M. graminicola, M. incognita, Pratylenchus vulnus, Heterodera glycines and Radopholus similis of Tylenchoidea. This phytogeny suggests that Aphelenchoides has a close relative relationship with Bursaphelenchus and that the Tylenchomorpha is not monophyletic.