新学術領域研「植物多能性幹細胞」

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Research - A01:Selected Projects -

[Core Research Groups A01 A02]  [Selected Projects A01 A02]

A01:Selected Research Projects

Generation and conversion of stem cells during two-step shoot regeneration

PI Munetaka Sugiyama Graduate School of Science, The University of Tokyo

Plants can regenerate organs through generation and conversion of stem cells. In plat tissue culture, two-step protocols, in which explants are first cultured on auxin-rich medium and then cultured on cytokinin-rich medium, are widely used for the induction of shoot regeneration. Recent findings show that, in this culture system, root apical meristem (RAM)-type stem cell niche is generated in response to auxin and converted into shoot apical meristem (SAM)-type stem cell niche in response to cytokinin. We have studied two-step shoot regeneration of Arabidopsis with various mutants and inhibitors, and obtained results suggesting that endogenous IAA alters the status of RAM-type stem cells and that RGD3, a gene encoding BTAF1, participates in the conversion into SAM-type stem cell niche. In the present research, we analyze roles of endogenous IAA and RGD3 in the two-step culture system with the aim of elucidating dynamics and regulations of stem cells during shoot regeneration.

Asymmetric division and cell cycle regulation in plant stem cells

PI Masaki Ito Institute of Science and Engineering,
Kanazawa University

A stem cell undergoes asymmetric division producing one daughter cell that behaves as original stem cell, and another daughter cells that is eventually differentiated into other type of cell. Plants achieved multicellularity independently of the animal lineages, and may have developed specific mechanisms for asymmetric division of stem cells during their own evolutional process. In this study, we focus especially on asymmetric divisions during stomatal development, and challenge the mechanisms for distributing different cell fates into two daughter cells. In our previous studies, we observed several cases where cell cycle regulators may affect cell division pattern and cell fate determination during stomatal development in Arabidopsis. Based on these observations, we will investigate the novel relationship of cell cycle regulation with asymmetric division and cell fate determination in plant stem cells.

Analysis of polarity formation and asymmetric cell division of stomatal stem cell

PI Tomoo Shimada Graduate School of Science, Kyoto University

Asymmetric cell division (ACD), which produces two distinct daughter cells, is a fundamental process that supports the development of multicellular land plants. Stomata, which are valves for gas exchange, are generated through several rounds of ACD. Previously, we identified and characterized a chemical compound, Bubblin, which affects stomatal stem cell polarity. Bubblin perturbed stomatal ACD, resulting in the generation of two identical daughter cells. The goal of this research is to elucidate molecular mechanisms responsible for the formation of cell polarity and ACD of stomatal stem cell.

Elucidation of the molecular mechanisms for auxin-mediated formation of pluripotent stem cells

PI Ryuichi Nishihama Graduate School of Biostudies, Kyoto University

Land plants perform 3D morphogenesis, which depends on the stem cells that have been formed de novo in the initial stage of development. The phytohormone auxin has been implicated in de novo formation of stem cells. However, its molecular mechanisms, especially for auxin-mediated gene regulation, remain to be clarified. In a basal land plant, the liverwort Marchantia polymorpha, young sporeling cells can give rise to all cell types and thus are in the totipotent state, while the stem cells in the thallus, so-called apical cells, are in the pluripotent state. Previous studies suggested that auxin signaling plays an essential role in the formation of apical cells. In this project, by making full use of characteristics and powerful genetics of M. polymorpha, we will elucidate the molecular mechanisms for auxin-mediated transition from the totipotent to pluripotent state, especially in terms of gene regulation and chromatin status. This study is expected to uncover the principle of stem cell formation conserved in land plants. Moreover, we will aim to define the totipotency and pluripotency of plant cells at the levels of gene expression and chromatin status.

Mechanisms of cell wall dependent stem cell fate determination

PI Keiko Sakakibara Graduate School of Science, Rikkyo University

Mechanical properties of cell wall are proposed to play an important role in stem cell and organ formation in land plants. However the mechanism of such regulation is not well-understood. We reported that two Physcomitrella patens WOX (WUSCHEL-related homeobox) homologs PpWOX13LA and PpWOX13LB, which are relatives of stem cell regulators in flowering plants, regulate new stem cell formation during protoplast regeneration through the up-regulation of cell wall loosening genes, such as β-expansins. We hypothesized that regulation of cell wall character is important to maintain the stemness of plant cell. To test the hypothesis, we will analyze the cell wall component and cell wall character of new stem cell in strains with genetic manipulation to modulate the level of cell wall controlling genes and its impact on the cell fate.

Molecular mechanisms controlling histone modification changes for stem cell formation in land plants

PI Masaki Ishikawa National Institute for Basic Biology

Epigenetic modifications, including histone modifications, function in stabilization of cell-specific gene expression programs to maintain cell identities in both metazoans and land plants. On the other hand, in land plants, de novo formation of stem cells is widely observed during post-embryonic development and regeneration, indicating that land plants have a high intrinsic ability to reprogram differentiated cells to stem cells. However, it has been unknown about molecular mechanisms that control the erasure of somatic epigenetic patterns. In the moss Physcomitrella patens, when a gametophore leaf is cut and incubated on culture medium, leaf cells facing the cut are reprogrammed to chloronema apical stem cells. In screens for factors involved in the reprogramming, we found that ectopic induction of STEMIN1 transcription factor directly changes gametophore leaf cells to chloronema apical stem cells. In this study, we aim to reveal molecular mechanisms implicated in the erasure of epigenetic information for stem cell formation by the STEMIN1 induction.

Molecular mechanisms underlying stem cell reformation by abiotic stresses

PI Akira Iwase RIKEN Center for Sustainable Resource Science

Vascular plants develop their tissues from thee different types of stem cells, which are located in the shoot apical meristem, root apical meristem and vascular cambium. Landmark studies showing whole plant regeneration from a single mesophyll protoplast clearly demonstrates that plants can reform all types of stem cells even from a differentiated cell. This reformation ability is often triggered by abiotic stress; however, the molecular mechanisms underlying this control remain poorly understood. In this study, we investigate how transcription factors mediate reformation of stem cells in Arabidopsis following abiotic stress.

Fate determination of haustorial stem cells in parasitic plants in Orobanchaceae

PI Satoko Yoshida Institute for Research Initiatives,
Nara Institute of Science and Technology

Parasitic plants in Orobanchaceae form an invasive organ haustorium on their roots in response to host signal. The haustorial apex contains highly dividing meristem-like cells, which we designate haustorial stem cells. The haustorial stem cells keep dividing until the haustorial apex reaches host tissues, and after reaching host tissues they transform to intrusive cells, special cells with elongated shape and a function for host intrusion. In this project, we will investigate fate determination mechanisms of haustorial stem cells, using parasitic plant mutants that have defects in regulation of cell division and fate transition of the haustorial apex.