Functional characterisation of the two-component signalling system of Arabidopsis

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The objective of the proposal is to study specific aspects of the function of the two-component signalling system (TCS) in Arabidopsis. The TCS is, among the higher eukaryotes, unique to plants. Arabidopsis harbours eight hybrid sensor kinases (AHKs), five histidine phosphotransfer proteins (AHPs) and 22 genes encoding two different types of response regulators (type A and type B ARR genes). Most of the functions of members of the TCS, in particular in which signalling pathway they participate and how they realize information transfer via interactions with other proteins of Arabidopsis and through gene activation are unknown. We will contribute to an improved understanding of the TCS in two ways. We have cloned and expressed most of the TCS genes in order to identify proteinprotein interactions between proteins of the TCS and other proteins of the Arabidopsis proteome by means of twohybrid screens and affinity co-purification coupled with mass spectrometry. By genome-wide expression analysis we have identified a set of immediate early response genes to cytokinin, which signals through the TCS. These will serve, beside a general phenotypical analysis, as endogenous reporter genes to characterize single and multiple cytokinin receptor knockout mutants and lines expressing gain-of-function and dominant-negative TCS transcription factors in order to identify individual TCS pathways. The detailed analysis of these specific aspects of the TCS is complementary to programmes of other groups participating in AFGN or the 2010 project.