The 26S Proteasome Regulatory Subunit GmPSMD Promotes Resistance to in Soybean.

Phytophthora root rot, caused by is a destructive disease of soybean () worldwide. We previously confirmed that the bHLH transcription factor GmPIB1 (-inducible bHLH transcription factor) reduces accumulation of reactive oxygen species (ROS) in cells by inhibiting expression of the peroxidase-related gene thus improving the resistance of hairy roots to . To identify proteins interacting with GmPIB1 and assess their participation in the defense response to , we obtained transgenic soybean hairy roots overexpressing GmPIB1 by mediated transformation and examined GmPIB1 protein-protein interactions using immunoprecipitation combined with mass spectrometry. We identified 392 proteins likely interacting with GmPIB1 and selected 20 candidate genes, and only 26S proteasome regulatory subunit GmPSMD (Genbank accession no. XP_014631720) interacted with GmPIB1 in luciferase complementation and pull-down experiments and yeast two-hybrid assays. Overexpression of (OE) in soybean hairy roots remarkably improved resistance to and RNA interference of ( -RNAi) increased susceptibility. In addition, accumulation of total ROS and hydrogen peroxide (HO) in OE transgenic soybean hairy roots were remarkably lower than those of the control after infection. Moreover, in -RNAi transgenic soybean hairy roots, HO and the accumulation of total ROS exceeded those of the control. There was no obvious difference in superoxide anion (O ) content between control and transgenic hairy roots. Antioxidant enzymes include peroxidase (POD), glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT) are responsible for ROS scavenging in soybean. The activities of these antioxidant enzymes were remarkably higher in -OE transgenic soybean hairy roots than those in control, but were reduced in -RNAi transgenic soybean hairy roots. Moreover, the activity of 26S proteasome in -OE and -OE transgenic soybean hairy roots was significantly higher than that in control and was significantly lower in -RNAi soybean hairy roots after infection. These data suggest that might reduce the production of ROS by improving the activity of antioxidant enzymes such as POD, SOD, GPX, CAT, and plays a significant role in the response of soybean to . Our study reveals a valuable mechanism for regulation of the pathogen response by the 26S proteasome in soybean.