题目：How are regulated vascular stem cell fates in plants?
讲座人：Hiroo Fukuda, PhD.
Department of Biological Sciences
Graduate School of Science
University of Tokyo
In vascular meristem, procambial and cambial cells act as vascular stem cells to give rise to various types of phloem and xylem cells. We have studied intensively the regulation of vascular stem cell fates, using newly established culture systems, transcriptomics, various mutants and molecular markers. Here, I will report recent understanding of sophisticated regulation of vascular stem cell fates mostly through our recent findings. In brief, a CLE peptide, tracheary element differentiation inhibitory factor (TDIF) is a crucial factor of stem cell maintenance. TDIF is secreted from phloem cells and perceived by a receptor TDR/PXY on procambial cells. TDIF-TDR suppresses the differentiation of procambial cells into xylem cells and promotes procambial cell division. Further analysis revealed factors downstream of TDIF-TDR signaling, glycogen synthase kinase 3 proteins (GSK3s), BES1 and WOX4. Importantly, using an inhibitor of plant GSK3s, we could establish a novel vascular differentiation system, “Vascular cell Induction culture System Using Arabidopsis Leaves (VISUAL)”, in which Arabidopsis mesophyll cells differentiate into not only xylem but also phloem cells. This result clearly indicates that GSK3s regulate both xylem and phloem differentiation from stem cells.
Furthermore, we investigated vascular stem cell initiation. We found that DELLA suppresses transdifferentiation from mesophyll cells into procambial cells in VISUAL. We also revealed that xylem precursor cells function as a vascular stem cell organizer in early vascular development. In this process, local cytokinin biosynthesis induced by a heterodimer of two bHLH transcription factors, LHW and TMO5/T5L1, in the xylem precursor cells contributes to the promotion of procambial cell division. Based on these novel findings, we will discuss about regulation of vascular stem cell fates.
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