Seminar "Elucidation of molecular mechanisms regulating vessel cell differentiation through the control of activity of Arabidopsis VND7, a NAC transcription factor" by Dr. Risaku Hirai

Speaker: Dr. Risaku Hirai, Nara Institute Science and Technology

Title: Elucidation of molecular mechanisms regulating vessel cell differentiation through the control of activity of Arabidopsis VND7, a NAC transcription factor

Abstract:

Xylem vessels are important for water conduction in vascular plants. The VASCULAR-RELATED NAC-DOMAIN (VND) family proteins, master regulators of xylem vessel cell differentiation in Arabidopsis thaliana, can upregulate a set of genes required for xylem vessel cell differentiation, including those involved in secondary cell wall (SCW) formation and programmed cell death (PCD). Expression of VND genes are known to be influenced by salt stress, cellular redox state and infections. Nevertheless, the relationship between VND activity and stress responses are unclear. Here, we examined the Arabidopsis VND7-VP16-GR line, in which VND7 activity is post-translationally activated by treatments with different concentrations of dexamethasone (DEX), a synthetic glucocorticoid. Our observations showed that low DEX induced partial SCW deposition, but not PCD, whereas higher DEX concentrations induced both SCW deposition and PCD. Moreover, the lower DEX concentrations delayed the upregulation of VND7 downstream genes, and decreased their expression levels. They collectively suggest that the regulation of VND activity is important not only to initiate xylem vessel cell differentiation, but also to regulate the expression of the PCD- and SCW-related genes throughout differentiation. Moreover, I performed a chemical screen to identify chemicals that affect xylem vessel cell differentiation under control of VND7-VP16-GR. I Identified the histone deacetylase inhibitors Trichostatin A and Sirtinol, as suppressors of xylem vessel cell differentiation. Expression analysis revealed VND7 downstream genes were downregulated and transcription factors which suppress xylem vessel cell were upregulated. Following mutant analyses indicated that the transcription repressor complex is responsible for suppression of xylem vessel cell differentiation by Trichostatin A. In summary, our data shows that VND7 ability to induce and regulate xylem cell differentiation is regulated at both the post-translational level and the epigenetic level.

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