ROS burst and MAPK activation are two independent signaling events after plant sensing of flg22.
FLS2-mediated sensing of flg22 activated two MAPK cascades. Among them, MPK3/MPK6 cascade is independent of AtRbohD-mediated ROS burst. In contrast, the lack of functional MPK4 results in an enhanced ROS burst, similar to the potentiation effect seen in SA-pretreated seedlings. SA-enhanced ROS burst is dependent on NPR1 and can be abolished by NahG transgene.