The plant MAPK cascades have pivotal roles in the regulation of plant development and in responses to a variety of stress stimuli, including pathogen infection, wounding, temperature, drought, salinity, osmolarity, UV irradiation, ozone and reactive oxygen species. In a general model of the MAPK signalling cascade, activation of plasma membrane receptors activates the MAPK kinase kinases. These are serine or threonine kinases that phosphorylate a conserved S/T-X325-S/T motif of the downstream MAPK kinases, which, in turn, phosphorylate MAPKs on threonine and tyrosine residues in a conserved T-X-Y motif of their activation loop. Following this MKK alteration of the phosphorylation-dependent properties of their target proteins, the activated MAPKs translate the information further, which eventually leads to changes in, e.g., gene expression, cellular redox state, or cell integrity. During pathogen attack, MAPK signalling is an indispensable component of the host defence response, in a way that it is involved in the crosstalk between secondary messengers and hormones. The key hormones in plant biotic interactions include the salicylates, jasmonates and ethylene, whereby their specific roles depend on the particular host�Cpathogen interaction. Many studies have indicated that salicylic acid is a key regulatory compound in disease resistance against fungi, bacteria and viruses. To date, a large number of members of the MAPK cascades from LY2874455 different species have been investigated, although to the best of our knowledge, there has been no systematic investigation of the MKK family and its function in defence signalling in potato. Moreover, no MAPK immune response network module has been defined for potato �C PVY interactions. We thus first performed sequence analysis of the complete MKK gene family in potato, and of its close relatives, where their genomes have been sequenced. Based on the present transcriptome data, StMKK6 was identified as the most responsive member after viral attack. We further Pimobendan investigated the role of StMKK6 in the response to PVY infection at the gene expression level, and studied its intracellular localisation and identified its downstream targets in the MAPK signalling cascade.