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, GmSKP1 which was significantly induced by P. sojae, was reported. The expression of GmSKP1 was simultaneously induced by methyl jasmonate (MeJA), salicylic acid (SA) and ethylene (ET), which might suggest an important role for GmSKP1 of plant in responses to hormone treatments. Functional analysis using GmSKP1 overexpression lines showed that GmSKP1 enhanced resistance to P. sojae in transgenic soybean plants. Further analyses showed that GmSKP1 interacted with a homeodomain-leucine zipper protein transcription factor (GmHDL56) and a WRKY transcription factor (GmWRKY31), which could positively regulate responses to P. sojae in soybean. Importantly, several pathogenesis-related (PR) genes were constitutively activated, including GmPR1a, GmPR2, GmPR3, GmPR4, GmPR5a and GmPR10, in GmSKP1-OE soybean plants. Taken together, these results suggested that GmSKP1 enhanced resistance to P. sojae in soybean, possibly by activating the defense-related PR genes.