Plants secrete defense molecules into the extracellular space (the apoplast) to combat attacking microbes. However, the mechanisms by which successful pathogens subvert plant apoplastic immunity remain poorly understood. In this study, we show that PsAvh240, a membrane-localized effector of the soybean pathogen Phytophthora sojae, promotes P. sojae infection in soybean hairy roots. We found that PsAvh240 interacts with the soybean-resistant aspartic protease GmAP1 in planta and suppresses the secretion of GmAP1 into the apoplast. By solving its crystal structure we revealed that PsAvh240 contain six a helices and two WY motifs. The first two a helices of PsAvh240 are responsible for its plasma membrane-localization and are required for PsAvh240's interaction with GmAP1. The second WY motifs of two PsAvh240 molecules form a handshake arrangement resulting in a handshake-like dimer. This dimerization is required for the effector's repression of GmAP1 secretion. Taken together, these data reveal that PsAvh240 localizes at the plasma membrane to interfere with GmAP1 secretion, which represents an effective mechanism by which effector proteins suppress plant apoplastic immunity.

Chromium coatings have been in widespread use to enhance the high-temperature oxidation resistance of low-alloy steels since the 1950s [Samuel and Lockington, Metal Treatment and Drop forgeing 18, 354 (1951); Sully and Brandes, Chromium, 2nd edn. Butterworths, London 1967]. In this work, a novel CeO 2 -dispersed chromium coating with a finegrain structure was manufactured on a mild-carbon steel by prior composite electrodeposition of Ni with CeO 2 particles, followed by chromizing using a conventionall halide activate, pack-cementation method. For comparison, chromizing was also performed on the carbon steel and on the one with Niplating pretreatment. Cyclic oxidation at 840 • C for 120 h showed that among the three various samples chromized, the CeO 2 -dispersed chromium coating exhibited the best oxidation resistance, while the worst for the coating on the carbon steel. The samples after oxidation were investigated using Xray diffraction (XRD), scanning-electron microscopy equipped with energy dispersive X-ray analysis (SEM/EDAX) and electron-probe microanalysis (EPMA). The results indicated that although all three coatings grew chromia scales during oxidation, the one formed on the CeO 2 -modifed coating was thinner, denser and had a fine-grain structure. Moreover, the formation of "Kirkendall" voids and new precipitates, which occurred during oxidation below the scale in the chromium coating on the Ni-plated sample, was prevented in the presence of CeO 2 particles in the coating. The CeO 2 effects on the coating formation and the coating oxidation behavior are discussed in detail.