(A) The PSR inhibits flg22-induced MAPK activation in a PHR1-dependent manner. Col-0 and phr1 mutant seedlings grown in either HP or LP media were treated with flg22 for 15 min and roots were harvested. The MAPK level was determined with anti-pMAPK, and β-actin was used as a loading control. Data information: All experiments were repeated three times with similar results. 