In the last decade, major components of the cytokinin (CK) signalling pathway governing developmental changes in transcription have been identified. However, in addition to the well known CK-activated multistep phosphorelay pathway, CK signalling and the mobilisation of developmental responses is expected to involve rapid, transcription-independent interactions of the CK pathway with unknown determinants, leading to changes in CK sensitivity and gene targeting. Our recent result indicate that three, CK-sensitive Ser/Thr kinases function as important modulators of CK effects on root development, indicating that phosphorylation events play an essential role in shaping the global CK response. Using mutants in CK signalling and lines deficient in these three kinases, we will analyse their role in the transcription-independent and early effects of CK on the proteome/phosphoproteome during CK-inhibition of root elongation in Arabidopsis. This analysis will potentially describe the differing impacts of CK on phosphorylation events/cascades from other signal pathways.

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