GmSKP1, a Novel S-phase Kinase-associated Protein 1 in Glycine max, Enhancing Resistance Against Phytophthora sojae Infection

Phytophthora root and stem rot of soybean caused by Phytophthora sojae（P. sojae） is a devastating disease that affects soybean Glycine max（L.） Merr. all over the world. S-phase kinase-associated protein 1（SKP1） proteins are key members of the SKP1/Cullin/F-box protein（SCF） ubiquitin ligase complex and play diverse roles in plant biology. However, the role of SKP1 in soybean against the phytopathogenic oomycete P. sojae remains unclear. In this study, a novel member of the soybean SKP1 gene family, Gm SKP1 which was significantly induced by P. sojae, was reported. The expression of Gm SKP1 was simultaneously induced by methyl jasmonate（Me JA）, salicylic acid（SA） and ethylene（ET）, which might suggest an important role for Gm SKP1 of plant in responses to hormone treatments. Functional analysis using Gm SKP1 overexpression lines showed that Gm SKP1 enhanced resistance to P. sojae in transgenic soybean plants. Further analyses showed that Gm SKP1 interacted with a homeodomain-leucine zipper protein transcription factor（Gm HDL56） and a WRKY transcription factor（Gm WRKY31）, which could positively regulate responses to P. sojae in soybean. Importantly, several pathogenesis-related（PR） genes were constitutively activated, including Gm PR1a, Gm PR2, Gm PR3, Gm PR4, Gm PR5a and Gm PR10, in Gm SKP1-OE soybean plants. Taken together, these results suggested that Gm SKP1 enhanced resistance to P. sojae in soybean, possibly by activating the defense-related PR genes.