Two leucines in the N-terminal MAPK-docking site of tomato SlMKK2 are critical for interaction with a downstream MAPK to elicit programmed cell death associated with plant immunity

Tomato MAPK kinase SlMKK2 is a key protein regulating immunity-associated programmed cell death (PCD) in plants. We examined the role of the N-terminal MAPK-docking site (or D-site) of SlMKK2 in PCD elicitation. In vivo assays revealed that SlMKK2 interacted with the downstream MAPK SlMPK3 independent of PCD elicitation and two conserved leucines in the D-site were required for both interaction with SlMPK3 and PCD elicitation. These results demonstrate that two leucines in the D-site of SlMKK2 play a critical role in regulation of signal transfer to the downstream MAPK by regulating their physical interaction.