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UBC Theses and Dissertations

Analysis of signaling from an unusual MAPKK (AtMKK3) in Arabidopsis thaliana Lampard, Gregory Raymond


Plants have developed numerous ways of adapting to a wide variety of environmental conditions. Mitogen-activated protein kinases (MAPKs) are a class of signaling molecules [i.e. signalling molecules] that are involved both in the detection of fluctuating environments and initiation of appropriate responses. MAPKs and their upstream activators, MAPK kinases (MAPKKs) are also involved in many additional physiological events, including the response to phytohormones, cell growth, cell death, differentiation and cell cycle control. It is thought that signal specificity and integration amongst MAPK signaling modules often occurs at the MAPKK level. MKK3 is a particularly interesting MAPKK because it is phylogenetically distinct from other plant MAPKKs, and uniquely contains both a canonical MAPKK S/T/Y dual-specificity protein kinase domain and a ’Nuclear Transport Factor 2’ (NTF2) domain. In this thesis I demonstrate, using a range of reverse genetics approaches, that MKK3 appears to be involved in the response of Arabidopsis thaliana to specific environmental stresses (salt, osmotic and heat stresses) and phytohormones (auxin and ABA), and may also have functions in plant development. Through protein interaction studies and in vitro activity assays, I also identified a potential novel negative regulatory influence of MKK3 on MAPK signaling modules involving three MAPKs, MPK1, MPK2 and MPK7. This pattern is the first such report for plant MAPK signaling modules. My protein interaction studies also revealed a possible role for the NTF2 domain in mediating the pair-wise interactions between MKK3 and each of MPK1, MPK2 and MPK7. These results provide a platform that should facilitate future studies of specificity and cross-talk amongst MKK3-associated MAPK signaling modules in higher plants.

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