Plant-parasitic
cyst nematodes successfully exploit various
phytohormone signaling pathways to establish a new hormonal equilibrium that facilitates nematode parasitism. Although it is largely accepted that
ethylene regulates plant responses to
nematode infection, a mechanistic understanding of how
ethylene shapes plant-nematode interactions remains largely unknown. In this study, we examined the involvement of various components regulating
ethylene perception and signaling in establishing Arabidopsis susceptibility to the
cyst nematode Heterodera schachtii using a large set of well-characterized single and higher order mutants. Our analyses revealed the existence of two pathways that separately engage
ethylene with
salicylic acid (SA) and
cytokinin signaling during plant response to
nematode infection. One pathway involves the canonical
ethylene signaling pathway in which activation of
ethylene signaling results in suppression of SA-based immunity. The second pathway involves the
ethylene receptor ETR1, which signals independently of SA
acid to affect immunity, instead altering
cytokinin-mediated regulation of downstream components. Our results reveal important mechanisms through which
cyst nematodes exploit components of
ethylene perception and signaling to affect the balance of hormonal signaling through
ethylene interaction with SA and
cytokinin networks. This hormonal interaction overcomes plant defense and provokes a susceptible response.