More Like this

1. Combined computational modeling and experimental analysis integrating chemical and mechanical signals suggests possible mechanism of shoot meristem maintenance

   https://doi.org/10.1371/journal.pcbi.1010199  

   Banwarth-Kuhn, Mikahl; Rodriguez, Kevin; Michael, Christian; Ta, Calvin-Khang; Plong, Alexander; Bourgain-Chang, Eric; Nematbakhsh, Ali; Chen, Weitao; Roy-Chowdhury, Amit; Reddy, G. Venugopala; et al (June 2022, PLOS Computational Biology)

   Nie, Qing (Ed.)

   Stem cell maintenance in multilayered shoot apical meristems (SAMs) of plants requires strict regulation of cell growth and division. Exactly how the complex milieu of chemical and mechanical signals interact in the central region of the SAM to regulate cell division plane orientation is not well understood. In this paper, simulations using a newly developed multiscale computational model are combined with experimental studies to suggest and test three hypothesized mechanisms for the regulation of cell division plane orientation and the direction of anisotropic cell expansion in the corpus. Simulations predict that in the Apical corpus, WUSCHEL and cytokinin regulate the direction of anisotropic cell expansion, and cells divide according to tensile stress on the cell wall. In the Basal corpus, model simulations suggest dual roles for WUSCHEL and cytokinin in regulating both the direction of anisotropic cell expansion and cell division plane orientation. Simulation results are followed by a detailed analysis of changes in cell characteristics upon manipulation of WUSCHEL and cytokinin in experiments that support model predictions. Moreover, simulations predict that this layer-specific mechanism maintains both the experimentally observed shape and structure of the SAM as well as the distribution of WUSCHEL in the tissue. This provides an additional link between the roles of WUSCHEL, cytokinin, and mechanical stress in regulating SAM growth and proper stem cell maintenance in the SAM. 

   more » « less
2. Cell-Based Model of the Generation and Maintenance of the Shape and Structure of the Multilayered Shoot Apical Meristem of Arabidopsis thaliana

   https://doi.org/10.1007/s11538-018-00547-z  

   Banwarth-Kuhn, Mikahl; Nematbakhsh, Ali; Rodriguez, Kevin W.; Snipes, Stephen; Rasmussen, Carolyn G.; Reddy, G. Venugopala; Alber, Mark (December 2018, Bulletin of Mathematical Biology)

   One of the central problems in animal and plant developmental biology is deciphering how chemical and mechanical signals interact within a tissue to produce organs of defined size, shape, and function. Cell walls in plants impose a unique constraint on cell expansion since cells are under turgor pressure and do not move relative to one another. Cell wall extensibility and constantly changing distribution of stress on the wall are mechanical properties that vary between individual cells and contribute to rates of expansion and orientation of cell division. How exactly cell wall mechanical properties influence cell behavior is still largely unknown. To address this problem, a novel, subcellular element computational model of growth of stem cells within the multilayered shoot apical meristem (SAM) of Arabidopsis thaliana is developed and calibrated using experimental data. Novel features of the model include separate, detailed descriptions of cell wall extensibility and mechanical stiffness, deformation of the middle lamella, and increase in cytoplasmic pressure generating internal turgor pressure. The model is used to test novel hypothesized mechanisms of formation of the shape and structure of the growing, multilayeredSAMbased onWUSconcentration of individual cells controlling cell growth rates and layer-dependent anisotropic mechanical properties of subcellular components of individual cells determining anisotropic cell expansion directions. Model simulations also provide a detailed prediction of distribution of stresses in the growing tissue which can be tested in future experiments. 

   more » « less
3. ERECTA family signaling constrains CLAVATA3 and WUSCHEL to the center of the shoot apical meristem

   https://doi.org/10.1242/dev.189753  

   Zhang, Liang; DeGennaro, Daniel; Lin, Guangzhong; Chai, Jijie; Shpak, Elena D. (March 2021, Development)

   null (Ed.)

   ABSTRACT The shoot apical meristem (SAM) is a reservoir of stem cells that gives rise to all post-embryonic above-ground plant organs. The size of the SAM remains stable over time owing to a precise balance of stem cell replenishment versus cell incorporation into organ primordia. The WUSCHEL (WUS)/CLAVATA (CLV) negative feedback loop is central to SAM size regulation. Its correct function depends on accurate spatial expression of WUS and CLV3. A signaling pathway, consisting of ERECTA family (ERf) receptors and EPIDERMAL PATTERNING FACTOR LIKE (EPFL) ligands, restricts SAM width and promotes leaf initiation. Although ERf receptors are expressed throughout the SAM, EPFL ligands are expressed in its periphery. Our genetic analysis of Arabidopsis demonstrated that ERfs and CLV3 synergistically regulate the size of the SAM, and wus is epistatic to ERf genes. Furthermore, activation of ERf signaling with exogenous EPFLs resulted in a rapid decrease of CLV3 and WUS expression. ERf-EPFL signaling inhibits expression of WUS and CLV3 in the periphery of the SAM, confining them to the center. These findings establish the molecular mechanism for stem cell positioning along the radial axis. 

   more » « less
4. Plant stem-cell organization and differentiation at single-cell resolution

   https://doi.org/10.1073/pnas.2018788117  

   Satterlee, James W.; Strable, Josh; Scanlon, Michael J. (December 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Plants maintain populations of pluripotent stem cells in shoot apical meristems (SAMs), which continuously produce new aboveground organs. We used single-cell RNA sequencing (scRNA-seq) to achieve an unbiased characterization of the transcriptional landscape of the maize shoot stem-cell niche and its differentiating cellular descendants. Stem cells housed in the SAM tip are engaged in genome integrity maintenance and exhibit a low rate of cell division, consistent with their contributions to germline and somatic cell fates. Surprisingly, we find no evidence for a canonical stem-cell organizing center subtending these cells. In addition, trajectory inference was used to trace the gene expression changes that accompany cell differentiation, revealing that ectopic expression of KNOTTED1 ( KN1 ) accelerates cell differentiation and promotes development of the sheathing maize leaf base. These single-cell transcriptomic analyses of the shoot apex yield insight into the processes of stem-cell function and cell-fate acquisition in the maize seedling and provide a valuable scaffold on which to better dissect the genetic control of plant shoot morphogenesis at the cellular level. 

   more » « less
5. Developmental changes in epidermal anatomy, drought tolerance, and biomechanics in the leaves of a tropical fern

   https://doi.org/10.1093/aob/mcaf204  

   Vieira-Goncalves, Daniel; Roddy, Adam B (September 2025, Annals of Botany)

   Throughout leaf development, cell expansion is dynamic and driven by the balance between local cell wall mechanical properties and the intracellular turgor pressure that overcomes the stiffness of the cell wall leading to plastic deformation. The epidermal pavement cells in most leaves begin development as small, polygonally shaped cells, but in mature leaves epidermal pavement cells are often shaped as highly lobed puzzle pieces. However, the developmental and biomechanical trajectories between these two end points have not before been fully characterized. Here we characterized how epidermal pavement cell size and shape, cell wall thickness, and hydraulic traits change during leaf expansion in the tropical understory fern Microsorum grossum (Polypodiaceae). As fronds expanded by approximately two orders of magnitude in size, epidermal pavement cells became increasingly lobed as cell walls thickened. Furthermore, the timing of these developmental changes varied across the lamina, start first near the frond base and midrib, followed by more apical and lateral regions. During expansion, fronds also underwent substantial physiological changes: as cells expanded and cell walls thickened, intracellular turgor pressure and the bulk cell wall modulus of elasticity both increased while the water potential at turgor loss and the minimum epidermal conductance to water vapor both decreased. These results highlight the dynamic coordination between anatomical and physiological traits throughout leaf development, provide valuable data for biophysical modeling of leaf development, and highlight the vulnerability of developing leaves to drought conditions. 

   more » « less