Constitutive activation of AtMEK5, a MAPK kinase, induces salicylic acidindependent cell death in Arabidopsis thaliana

In most circumstances, plants are able to defendthemselves against pathogen attack. The mechanisms ofplants resisting the invasion of pathogens often includeinduction of hypersensitive response (HR) cell death, theactivation of defense genes and the production of antim-icrobial phytoalexins1—3]. Plant defense responses are ini-tiated either by the interaction between a plant resistance(R) gene and a pathogen avirulence (avr) gene or by thebinding of a non-race-specific elicitor to its recep…

Constitutive activation of AtMEK5, a MAPK kinase,induces salicylic acid-independent cell death in Arabidopsis thaliana

AtMEK₅ ^DD is an active mutant of AtMEK₅, a MAP kinase kinase in Arabidopsis. Induction of AtMEK₅ ^DD expression in transgenic plants leads to activation of 44 and 48 kD MAPKs and causes a rapid cell death. To compare the cell death induced by the expression of AtMEK₅ ^DD with the HR-cell death induced by avirulence pathogen infection, we analyzed the activation of downstream MAP Kinase and induction of PR genes expression in permanent transgenic Arabidopsis plants. In-gel kinase activity assay revealed that the infection of Pseudomonas syringae DC3000 harboring Avr Rpt2 gene also lead to activation of 44 and 48 kD MAPKs. PAL, PR1 and PR5 were strongly induced in plants undergoing HR-cell death caused by the infection of P. syringae DC3000, while only the expression of PR5 was strongly induced in transgenic plants expressing AtMEK₅ ^DD protein. NahG protein in AtMEK₅ ^DD × NahG plants cannot suppress the cell death induced by AtMEK₅ ^DD. And AtMEK₅ ^DD protein expressed AtMEK₅ ^DD × NahG plants showed no significant change in salicylic acid (SA) level. All these suggest that the cell death induced by the activation of AtMEK₅ is salicylic acid-independent.