Quantification of cell-type-specific plasmodesmata distribution in Arabidopsis roots reveals spatial and patterning dynamics.

Cell-to-cell communication underpins pattern formation and organ function in multicellular organisms. Plant cells can communicate directly through cytoplasmic channels called plasmodesmata. The distribution, abundance, and density of plasmodesmata on plant cell interfaces impact the flow of molecules between plant cells; yet the extent to which these properties are genetically and dynamically regulated remains poorly understood at an organ scale. We developed a quantitative approach to map plasmodesmata pit fields across roots in 3D at cell type and cell interface-specific resolution. Multiple parameters are captured simultaneously, including plasmodesmata pit field abundance, density, and spatial distribution, enabling parallel multiscale analyses at cellular resolution across this organ. During root maturation, plasmodesmata abundance increases, with the greatest biogenesis occurring within the inner cell layers. This is coupled with changes in the degree of clustering of the pit fields on these inner cell layers: becoming more dispersed on specific cell interface types and more clustered on others. Significant differences in plasmodesmata pit field spatial patterning were detected at cell type-specific resolution in the BRASSINOSTEROID INSENSITIVE1 mutant, demonstrating a role for this hormone pathway in channel patterning. The ability to quantify pit field abundance and patterning at cell type-specific resolution provides novel insight into the developmental and hormonal regulation of potential symplastic connectivity across plant organs, while providing a powerful tool toward the investigation of quantitative systems-level plasmodesmata distribution and macro-communication between cells in a complex multicellular system.