Abstract
Plant parasitic nematodes secrete effectors into host plant tissues to facilitate parasitism. In this study, we identified a G16B09-like effector protein family from the transcriptome of Heterodera avenae, and then verified that most of the members could suppress programmed cell death triggered by BAX in Nicotiana benthamiana. Ha18764, the most homologous to G16B09, was further characterized for its function. Our experimental evidence suggested that Ha18764 was specifically expressed in the dorsal gland and was dramatically upregulated in the J4 stage of nematode development. A Magnaporthe oryzae secretion system in barley showed that the signal peptide of Ha18764 had secretion activity to deliver mCherry into plant cells. Arabidopsis thaliana overexpressing Ha18764 or Hs18764 was more susceptible to Heterodera schachtii. In contrast, BSMV-based host-induced gene silencing (HIGS) targeting Ha18764 attenuated H. avenae parasitism and its reproduction in wheat plants. Transient expression of Ha18764 suppressed PsojNIP, Avr3a/R3a, RBP-1/Gpa2, and MAPK kinases (MKK1 and NPK1Nt)-related cell death in Nicotiana benthamiana. Co-expression assays indicated that Ha18764 also suppressed cell death triggered by four H. avenae putative cell-death-inducing effectors. Moreover, Ha18764 was also shown strong PTI suppression such as reducing the expression of plant defense-related genes, the burst of reactive oxygen species, and the deposition of cell wall callose. Together, our results indicate that Ha18764 promotes parasitism, probably by suppressing plant PTI and ETI signaling in the parasitic stages of H. avenae.
Highlights
Heterodera avenae is an important cereal cyst nematode (CCN) that infects wheat, barley, and oat crops in the cereal-growing regions worldwide
Western blotting confirmed the expression of H. avenae candidate effector protein, enhanced green fluorescent protein (eGFP), and BAX
Some plant-parasitic nematode effectors are present in large multi-gene families, and the G16B09 family is considered among the largest of effector families (Cotton et al, 2014)
Summary
Heterodera avenae is an important cereal cyst nematode (CCN) that infects wheat, barley, and oat crops in the cereal-growing regions worldwide. The infective second-stage juvenile (J2) of this cyst nematode penetrates the root tips of its host plant and migrates intracellularly toward the vascular cylinder, it inserts its stylet into a cell and induces the infusion of surrounding cells, resulting in the formation of a multinucleate syncytium (Jones, 1981). The same with other plant pathogens, nematodes can secrete effector proteins to regulate host. Heterodera avenae Effector Ha18764 plant cellular processes to promote their parasitism. Most of these effectors are produced in the esophageal glands and are delivered into plant cells via the nematode’s hollow stylet
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