Mitogen activated protein kinase (MAPK) pathways are crucial regulatory pathways in defense and development in plants. The ability to rapidly activate and deactivate MAPK pathways in response to changing conditions allows plants to adapt to a changing environment. tMEK2 is an important MAPK kinase in tomato plants and based on a high protein sequence similarity of 74.8% it may be closely related to an Arabidopsis thaliana MAPKK AtMEK1. AtMEK1 is a defense response gene that is capable of activating the MAPK proteins AtMPK3, AtMPK4, and AtMPK6. More information about the activity and roles of AtMEK1 is needed and to provide more information several tests were undertaken, examining AtMEK1's response to stresses through the use of knockout mutants of AtMEK1. We found that there was reduced response in AtMEKl knockouts in response to a synthetic auxin, an auxin transport inhibitor, as well as fungal toxin fumonisin B1. AtMEK1 mutant plants showed resistance to salt during both germination and adulthood. There was no visible difference in response to either cold or heat stress between wild type and knockout plants. AtMEK1 knockout Arabidopsis were also capable of bolting under short day conditions, unlike wild type plants. This shows that AtMEKl plays a role in a variety of developmental and stress response pathways.