Localized calcium transients in phragmoplast regulate cytokinesis of tobacco BY-2 cells

Plants exhibit a unique pattern of cytosolic Ca²⁺ dynamics to correlate with microtubules to regulate cytokinesis, which significantly differs from those observed in animal and yeast cells. Calcium (Ca²⁺) transients mediated signaling is known to be essential in cytokinesis across eukaryotic cells. However, the detailed spatiotemporal dynamics of Ca²⁺ during plant cytokinesis remain largely unexplored. In this study, we employed GCaMP5, a genetically encoded Ca²⁺ sensor, to investigate cytokinetic Ca²⁺ transients during cytokinesis in Nicotiana tabacum Bright Yellow-2 (BY-2) cells. We validated the effectiveness of GCaMP5 to capture fluctuations in intracellular free Ca²⁺ in transgenic BY-2 cells. Our results reveal that Ca²⁺ dynamics during BY-2 cell cytokinesis are distinctly different from those observed in embryonic and yeast cells. It is characterized by an initial significant Ca²⁺ spike within the phragmoplast region. This spike is followed by a decrease in Ca²⁺ concentration at the onset of cytokinesis in phragmoplast, which then remains elevated in comparison to the cytosolic Ca²⁺ until the completion of cell plate formation. At the end of cytokinesis, Ca²⁺ becomes uniformly distributed in the cytosol. This pattern contrasts with the typical dual waves of Ca²⁺ spikes observed during cytokinesis in animal embryonic cells and fission yeasts. Furthermore, applications of pharmaceutical inhibitors for either Ca²⁺ or microtubules revealed a close correlation between Ca²⁺ transients and microtubule organization in the regulation of cytokinesis. Collectively, our findings highlight the unique dynamics and crucial role of Ca²⁺ transients during plant cell cytokinesis, and provides new insights into plant cell division mechanisms.