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The root meristem is shaped by brassinosteroid control of cell geometry.

ABSTRACT: Growth extent and direction determine cell and whole-organ architecture. How they are spatio-temporally modulated to control size and shape is not well known. Here we tackled this question by studying the effect of brassinosteroid (BR) signalling on the structure of the root meristem. Quantification of the three-dimensional geometry of thousands of individual meristematic cells across different tissue types showed that the modulation of BR signalling yields distinct changes in growth rate and anisotropy, which affects the time that cells spend in the meristem and has a strong impact on the final root form. By contrast, the hormone effect on cell volume was minor, establishing cell volume as invariant to the effect of BR. Thus, BR has the highest effect on cell shape and growth anisotropy, regulating the overall longitudinal and radial growth of the meristem, while maintaining a coherent distribution of cell sizes. Moving from single-cell quantification to the whole organ, we developed a computational model of radial growth. The simulation demonstrates how differential BR-regulated growth between the inner and outer tissues shapes the meristem and thus explains the non-intuitive outcomes of tissue-specific perturbation of BR signalling. The combined experimental data and simulation suggest that the inner and outer tissues have distinct but coordinated roles in growth regulation.

SUBMITTER: Fridman Y

PROVIDER: S-EPMC8592843 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The mechanisms ensuring balanced growth remain a critical question in developmental biology. In plants, this balance relies on spatiotemporal integration of hormonal signaling pathways, but the understanding of the precise contribution of each hormone is just beginning to take form. Brassinosteroid (BR) hormone, is shown here to have opposing effects on root meristem size, depending on its site of action. BR is demonstrated to both delay and promote onset of stem cell daughter differentiation, when acting in the outer tissue of the root meristem, the epidermis, and the inner-most tissue, the stele, respectively. To understand the molecular basis of this phenomenon, a comprehensive spatiotemporal translatome mapping of Arabidopsis roots was performed. Analyses of wild type and mutants featuring different distributions of BR, revealed autonomous, tissue-specific gene responses to BR, implying its contrasting tissue-dependent impact on growth. BR-induced genes were primarily detected in epidermal cells of the basal meristem zone and were enriched by auxin-related genes. In contrast, repressed BR genes prevailed in the stele of the apical meristem zone. Furthermore, auxin was found to mediate the growth-promoting impact of BR signaling originating in the epidermis, while BR signaling in the stele buffered this effect. We propose that context-specific BR activity and responses are oppositely interpreted at the organ level, ensuring coherent growth. 24 samples of polyribosome-associated mRNA (following 0, 3, and 8 hours of BR treatment, in two biological repetitions), were collected. RNA samples were sequenced on an Illumina HiSeq 2500, to obtain 50 bp single-end reads. These reads were aligned to the TAIR10 assembly of the Arabidopsis thaliana genome, using Tophat2 v2.0.9. Transcript coordinates from the TAIR10 reference set were used to guide the alignment process. After alignment, the numbers of reads per transcript were estimated using HTSeq v0.5.3p3, and DESeq2 v1.2.8 was used to normalize read counts and call differentially expressed genes.

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The root meristem is shaped by brassinosteroid control of cell geometry.

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