In 2007, Ben Scheres proposed in his landmark review that the SCNs of plant and animal kingdoms are specified by kingdom-specific patterning mechanisms, but that connect to a related core of epigenetic stem-cell factors ( Scheres, 2007). Hence, ‘organizing’ cells maintain the stem-cells and SCNs by continuous short-range signaling. Similar to WUS, the pluripotency factor WOX5 maintains the stemness of the initials ( Sarkar et al., 2007). RAMs include mitotically less active organizer cells called the quiescent center (QC) and the surrounding initials, which together compose the root SCN. Along with the pluripotency factor SHOOT MERISTEMLESS (STM), WUS maintains the stem-cells that form with the OC the shoot SCN. In SAMs, the stem-cells, located at the top of the meristematic dome, secret the signal peptide CLAVATA3 (CLV3) that represses the pluripotency gene WUSCHEL ( WUS) in cells of the organizing center (OC) underneath the stem-cells ( Müller-Xing and Xing, 2021). Branched structures rise post-embryonically from secondary meristems initiated from a few cells that retain meristematic characteristics ( Nicolas and Laufs, 2022). Shoot and root apical meristem (SAM and RAM), which are formed during embryogenesis, only contributes to the main stem and main root, respectively. The SCN is surrounded by a transitory population of indeterminate cells that give rise to determinate cells and organs. Meristems contain a specialized cellular microenvironment known as stem-cell niche (SCN) that provides the signals and physical support to maintain the pluripotent stem-cells ( Sablowski, 2011). Unlike animals, plant growth and organ formation occur post-embryonically, mediated by meristems that are located on the tips of growth axes in shoots and roots ( Doerner, 2003). Here, we highlight recent breakthroughs but also revisited classical studies of epigenetic regulation and chromatin dynamics of plant stem-cells and their pluripotent precursor-cells, and point out open questions and future directions. Although, more and more epigenetic regulators have been shown to control plant stem-cell fate, only a few studies demonstrate how they are recruited and how they change the chromatin structure and transcriptional regulation of pluripotency factors. ![]() It is now clear that, in addition to gene regulatory networks of pluripotency factors and phytohormone signaling, epigenetics play a crucial role in initiation, maintenance and determination of plant stem-cells. ![]() Hence, in contrast to the widely-held assumption that all plant cells have the ability to reproduce a complete organism, only few cell types are pluripotent in practice, raising the question how pluripotent stem-cells differ from differentiated cells. In tissue cultures, after detached plant organs are transferred to rooting or callus induction medium (G5 or CIM), vasculature-associated pluripotent cells (VPCs) immediately start proliferation to form adventitious roots or callus, respectively, while other cell types of the organ explants basically play no part in the process. After ablation of stem-cell niches, pluripotent meristematic cells can establish new stem-cells, whereas the removal of the whole meristem destructs the regeneration process. In plants, stem-cells are located in specific niches of the shoot and root apical meristems (SAMs and RAMs). ![]() ![]() Pluripotent stem-cells are slowly dividing cells giving rise to daughter cells that can either differentiate to new tissues and organs, or remain stem-cells. Lushan Botanical Garden, Chinese Academy of Sciences, Jiujiang, China.
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