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Authors: Jefri Heyman and Lieven De Veylder
Journal of Experimental Botany (2024)
Summary: "Stem cells are generally described as cells that exist in an undifferentiated or only partially differentiated state. When they divide, they give rise to two daughter cells, one of which retains its stem cell-like properties, while the other sibling generally differentiates and adopts the cell fate of the surrounding tissue. By selectively killing stem cells using radiomimetic drugs, Takahashi et al. (2024) uncovered a signaling module in the Arabidopsis thaliana root that awakens dormant stem cells to help replace stem cells lost through DNA damage."
Authors: Canran Sun, Yang Liu, Guofang Li, Yanle Chen, Mengyuan Li, Ruihua Yang, Yongtian Qin, Yongqiang Chen, Jinpeng Cheng, Jihua Tang and Zhiyuan Fu.
The Crop Journal (2024)
Abstract: "Plant height (PH) is associated with lodging resistance and planting density, which is regulated by a complicated gene network. In this study, we identified a spontaneous dwarfing mutation in maize, m30, with decreased internode number and length but increased internode diameter. A candidate gene, ZmCYP90D1, which encodes a member of the cytochrome P450 family, was isolated by map-based cloning. ZmCYP90D1 was constitutively expressed and showed highest expression in basal internodes, and its protein was targeted to the nucleus. A G-to-A substitution was identified to be the causal mutation, which resulted in a truncated protein in m30. Loss of function of ZmCYP90D1 changed expression of hormone-responsive genes, in particular brassinosteroid (BR)-responsive genes which is mainly involved in cell cycle regulation and cell wall extension and modification in plants. The concentration of typhasterol (TY), a downstream intermediate of ZmCYP90D1 in the BR pathway, was reduced. A haplotype conferring dwarfing without reducing yield was identified. ZmCYP90D1 was inferred to influence plant height and stalk diameter via hormone-mediated cell division and cell growth via the BR pathway."
Authors: Wenyi Wang, Vanika Garg, Rajeev K. Varshney and Hao Liu.
Trends in Plant Science (2023).
Abstract: Phytohormone signaling regulates plant growth and development. Single cell RNA sequencing (scRNA-seq) provides unprecedented opportunities to decipher hormone-mediated spatiotemporal gene regulatory networks. In a recent study, Nolan et al. used time-series scRNA-seq to identify the cortex as a key site for brassinosteroid (BR)-mediated gene expression and revealed a signaling network during cell phase transition."
Authors: Yi Zhang, Tongda Xu and Juan Dong.
Journal of Integrative Plant Biology (2023)
Abstract: "Asymmetric cell division is a fundamental process that generates new cell types during development in eukaryotic species. In plant development, post-embryonic organogenesis driven by asymmetric cell division is more universal and important than in animals, in which organ pattern is preset during embryogenesis. Thus, plant development provides a powerful system to study molecular mechanisms underlying asymmetric cell division. During the past decade, tremendous progress has been made in our understanding of the key components and mechanisms involved in this important process in plants. Here, we present an overview on how asymmetric cell division is determined and regulated in multiple biological processes in plant development and compare their conservation and specificity among different model cell systems. We also summarize the molecular roles and mechanisms for the phytohormones in the regulation of plant asymmetric cell division. Finally, we conclude with the overarching paradigms and principles that govern plant asymmetric cell division and consider how new technologies can be exploited to fill the knowledge gaps and make new advances in the field."
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Authors: Naoki Takahashi, Kazuki Suita, Toshiya Koike, Nobuo Ogita, Ye Zhang and Masaaki Umeda.
Journal of Experimental Botany (2024)
One-sentence summary: DNA double-strand breaks promote regenerative cell division at the quiescent center in Arabidopsis roots by elevating the expression of the brassinosteroid receptor gene BRL3.
Abstract: "In Arabidopsis roots, the quiescent center (QC), a group of slowly dividing cells located at the center of the stem cell niche, functions as an organizing center to maintain the stemness of neighboring cells. Recent studies have shown that they also act as a reservoir for backup cells, which replenish DNA-damaged stem cells by activating cell division. The latter function is essential for maintaining stem cells under stressful conditions, thereby guaranteeing post-embryonic root development in fluctuating environments. In this study, we show that one of the brassinosteroid receptors in Arabidopsis, BRASSINOSTEROID INSENSITIVE1-LIKE3 (BRL3), plays a major role in activating QC division in response to DNA double-strand breaks. SUPPRESSOR OF GAMMA RESPONSE 1, a master transcription factor governing DNA damage response, directly induces BRL3. DNA damage-induced QC division was completely suppressed in brl3 mutants, whereas QC-specific overexpression of BRL3 activated QC division. Our data also showed that BRL3 is required to induce the AP2-type transcription factor ETHYLENE RESPONSE FACTOR 115, which triggers regenerative cell division. We propose that BRL3-dependent brassinosteroid signaling plays a unique role in activating QC division and replenishing dead stem cells, thereby enabling roots to restart growing after recovery from genotoxic stress."
Authors: Eun-Ji Kim, Cheng Zhang, Boyu Guo, Thomas Eekhout, Anaxi Houbaert, Jos R. Wendrich, Niels Vandamme, Manish Tiwari, Claire Simon--Vezo, Isabelle Vanhoutte, Yvan Saeys, Kun Wang, Yuxian Zhu, Bert De Rybel and Eugenia Russinova.
PNAS (2022)
Significance: Stomata, the gas exchange pores in plant epidermis, are formed by series of cell divisions and cell-fate transitions. Stomatal development is tightly controlled by endogenous and environmental cues. The BIN2 kinase, a key negative regulator of brassinosteroid signaling controls stomatal development, but the role of brassinosteroid hormones remains unclear. Here, through mapping the single-cell transcriptome of stomatal lineage in Arabidopsis after activation of brassinosteroid signaling with either exogenous hormones or the plant-specific BIN2 inhibitor, bikinin, we showed that the scaffold proteins POLAR and PL1 insulate BIN2 from brassinosteroid-mediated inactivation specifically in stomatal precursors. Our study reveals how different cell types interpret hormonal signals to initiate cell type–specific responses and correct cell patterning.
Abstract: "In Arabidopsis thaliana, brassinosteroid (BR) signaling and stomatal development are connected through the SHAGGY/GSK3-like kinase BR INSENSITIVE2 (BIN2). BIN2 is a key negative regulator of BR signaling but it plays a dual role in stomatal development. BIN2 promotes or restricts stomatal asymmetric cell division (ACD) depending on its subcellular localization, which is regulated by the stomatal lineage-specific scaffold protein POLAR. BRs inactivate BIN2, but how they govern stomatal development remains unclear. Mapping the single-cell transcriptome of stomatal lineages after triggering BR signaling with either exogenous BRs or the specific BIN2 inhibitor, bikinin, revealed that the two modes of BR signaling activation generate spatiotemporally distinct transcriptional responses. We established that BIN2 is always sensitive to the inhibitor but, when in a complex with POLAR and its closest homolog POLAR-LIKE1, it becomes protected from BR-mediated inactivation. Subsequently, BR signaling in ACD precursors is attenuated, while it remains active in epidermal cells devoid of scaffolds and undergoing differentiation. Our study demonstrates how scaffold proteins contribute to cellular signal specificity of hormonal responses in plants."
Authors: Kyoko Ohashi-Ito, Kuninori Iwamoto, Ayumi Yamagami, Takeshi Nakano and Hiroo Fukuda.
PNAS (2023)
Significance Plants grow via the organized division of various initial cells in meristems. In the root apical meristem (RAM), periclinal division of vascular cells is controlled by phytohormones and crucial transcription factors (TFs) including HD-ZIP III (class III homeodomain leucine zipper) family proteins. In this study, we found that HD-ZIP III TFs positively regulate brassinosteroid biosynthesis–related genes in the vascular tissue. Genetic and physiological analyses with mutants of HD-ZIP III genes and a brassinosteroid biosynthesis gene suggested that brassinosteroid biosynthesis underlying HD-ZIP III regulation is a key event for the suppression of periclinal division of vascular cells. Brassinosteroid acted at suppression of cytokinin response, which induces the periclinal division of vascular cells.
Abstract: "Spatiotemporal control of cell division in the meristem is vital for plant growth. In the stele of the root apical meristem (RAM), procambial cells divide periclinally to increase the number of vascular cell files. Class III homeodomain leucine zipper (HD-ZIP III) proteins are key transcriptional regulators of RAM development and suppress the periclinal division of vascular cells in the stele; however, the mechanism underlying the regulation of vascular cell division by HD-ZIP III transcription factors (TFs) remains largely unknown. Here, we performed transcriptome analysis to identify downstream genes of HD-ZIP III and found that HD-ZIP III TFs positively regulate brassinosteroid biosynthesis–related genes, such as CONSTITUTIVE PHOTOMORPHOGENIC DWARF (CPD), in vascular cells. Introduction of pREVOLUTA::CPD in a quadruple loss-of-function mutant of HD-ZIP III genes partly rescued the phenotype in terms of the vascular defect in the RAM. Treatment of a quadruple loss-of-function mutant, a gain-of-function mutant of HD-ZIP III, and the wild type with brassinosteroid and a brassinosteroid synthesis inhibitor also indicated that HD-ZIP III TFs act together to suppress vascular cell division by increasing brassinosteroid levels. Furthermore, brassinosteroid application suppressed the cytokinin response in vascular cells. Together, our findings suggest that the suppression of vascular cell division by HD-ZIP III TFs is caused, at least in part, by the increase in brassinosteroid levels through the transcriptional activation of brassinosteroid biosynthesis genes in the vascular cells of the RAM. This elevated brassinosteroid level suppresses cytokinin response in vascular cells, inhibiting vascular cell division in the RAM."
Authors: Zhenni Li, Ayala Sela, Yulia Fridman, Lucía Garstka, Herman Höfte, Sigal Savaldi-Goldstein and Sebastian Wolf.
Development (2021)
Abstract: "Plant brassinosteroid hormones (BRs) regulate growth in part through altering the properties of the cell wall, the extracellular matrix of plant cells. Conversely, feedback signalling from the wall connects the state of cell wall homeostasis to the BR receptor complex and modulates BR activity. Here, we report that both pectin-triggered cell wall signalling and impaired BR signalling result in altered cell wall orientation in the Arabidopsis root meristem. Furthermore, both depletion of endogenous BRs and exogenous supply of BRs triggered these defects. Cell wall signalling-induced alterations in the orientation of newly placed walls appear to occur late during cytokinesis, after initial positioning of the cortical division zone. Tissue-specific perturbations of BR signalling revealed that the cellular malfunction is unrelated to previously described whole organ growth defects. Thus, tissue type separates the pleiotropic effects of cell wall/BR signals and highlights their importance during cell wall placement."
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