Activator of mRNA decapping. Involved in mRNA decay via decapping. Involved in disease resistance in response to biotrophic and necrotrophic pathogens. Is part of a signaling pathway including MPK4 and the disease resistance protein SUMM2. Interacts with MPK4 and SUMM2. Accumulates in response to flg22 (at protein levels). Phosphorylated at Ser-208 by MPK4 upon flg22 elicitation. Phosphorylated at Ser-200, Ser-342 and Ser-343 upon flg22 elicitation. Serrated leaf and reduced plant size. Constitutive expression of the defense-related gene PR1 and enhanced resistance to the bacterial pathogen Pseudomonas syringae pv tomato strain DC3000.