Abstract: Ethylene (ET) and Salicylic Acid (SA) are important modulators of plant growth,and also play a key role in regulating interactions between plant and plant-parasitic nematodes.However,their crucial cross-talks are unclear in a compatible susceptible soybean-Heterodera glycines (soybean cyst nematode,SCN) interaction.RNA-Seq analysis revealed that ET but not SA metabolism was activated in soybean roots infected with SCN for 24 h.Exogenous ethephon (ETH,ET donor) supply at 0.5 mM induced SCN susceptibility in the roots of William 82,and application of 2 mM SA markedly decreased the reproduction of SCN.However,the immune inducible effect of SA was at least partly compromised by ETH treatments.Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) confirmed that ETH supply led to reduce the expression of GmICS2,a gene of SA biosynthesis,suggesting the ET and SA pathway might be antagonistic in soybean roots.In addition,we found that the SA-induced resistance was associated with up-regulation of SA-responsive genes GmPR1 and GmPR2,whereas ETH treatment exhibited an inhibitory effect on the expression levels of GmPR2 and GmPR3 in SCN-infected roots.Collectively,these results indicate that ET plays a positive role in a compatible interaction between susceptible soybean and SCN,and the negative cross-talk between the ET and SA pathway may involve in modulating the outcome of soybean-SCN interaction.