Figure 9.

Model for priming by Phi for augmented defense responses in Arabidopsis infected with Hpa. Treatment with Phi inhibits the accumulation and phosphorylation of MPK4 after Hpa inoculation. The exact target(s) of Phi could be MPK4 or upstream components of the MAPK cascade as MEKK1 and MKK1/MKK2. Inactivation of MPK4 may also be mediated by Phase (for phosphatase protein[s]). Repression of MPK4 expression/MPK4 activity enhances PAD4 and EDS1 accumulation (dashed line) and triggers SA signaling-dependent priming for enhanced resistance through the defense regulatory protein NPR1.