Cytokinins control cell differentiation via negative regulation of secondary cell wall master regulators NST1 and NST3
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| Year of publication | 2015 |
| Type | Appeared in Conference without Proceedings |
| MU Faculty or unit | |
| Citation | |
| Description | Control over the equilibrium between cell division and cell differentiation represents the core developmental regulation across all kingdoms Plant hormones cytokinins were shown to regulate both the process of cell differentiation and cell proliferation. However, the molecular mechanism of cytokinin-controlled cell differentiation is far from being understood. Here we present the role of cytokinins in the control of differentiation program of secondary cell wall-containing cells. We found that impaired cytokinin signaling disturbs apical/basal developmental gradient in the inflorescence stem of Arabidopsis. Attenuated cytokinin signaling results in formation of vascular bundles with changed protoxylem/metaxylem ratio and formation of tracheary elements with reduced diameter and dramatically reduced water conductance. Increased lignification in both tracheary elements and xylem fibers suggested early cell differentiation. The genome-wide next-gen transcriptional profiling revealed ectopic upregulation of factors throughout the hierarchical transcriptional cascade including the NAC TFs NST1 and SND1/NST3, the master transcriptional switches of secondary cell wall formation. That leads to precocious activation of downstream structural components mediating the biosynthesis of xylan, lignin and cellulose, the main compounds of the secondary cell wall. Measurements of endogenous cytokinin levels indicated spatial specificity of cytokinin distribution along apical/basal axis of inflorescence stem. We found that disturbing the apical/basal cytokinin distribution via depleting endogenous cytokinin content or impairing cytokinin biosynthesis in atipt1,3,5,7 mutant phenocopies the early differentiation phenotype and functional defects of tracheary elements observed in the cytokinin signaling mutants. That associates with ectopic upregulation of NST1 and NST3 master regulators as well as downstream structural genes involved in secondary cell wall formation. Exogenous cytokinin application was able to downregulate the ectopic increase in NST1/NST3 expression and rescue the precocious differentiation phenotype in atipt1,3,5,7. The negative role of cytokinins in regulation of NSTs expression was confirmed by qRT PCR and downregulation of pNST3:NST3-GUS expression by exogenous cytokinins. Based on our findings we propose the role of cytokinins as a positional cue controlling cell differentiation status via regulating expression of secondary cell wall master regulators NST1 and NST3 |
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