UC San Diego

PAN1 is a receptor-like protein that promotes polarization of the subsidiary mother cell (SMC) toward the adjacent guard mother cell (GMC) during asymmetric cell division in Zea Mays stomatal complexes. PAN1 localizes at the SMC and GMC contact site ("SMC patch site") and is thought to be involved in signal transduction, acting as a receptor or co-receptor of GMC derived signals. However, PAN1 is also found at the cell plate of symmetric and asymmetric divisions but its role here is unclear. In this study, the role of PAN1 at the cell plate was investigated. Analysis of pan mutants via acriflavine and high concentration propidium iodide staining showed misoriented divisions but no problems with cell plate completion. PAN2 and BRK1 are required for PAN1 recruitment to SMC patch sites but they are not cell plate localized and observation of PAN1-YFP in pan2 and brk1 mutants revealed that both are not required for PAN1 recruitment to the cell plate. PAN1 has been shown to stimulate localized actin polymerization at SMC patch sites, but no actin defects were observed in phragmoplasts or cell plates in pan mutants. Molecular markers of cell plate formation (callose, ARF, SCAMP, KNOLLE, and PATL1) were also examined in pan mutants; no defects in recruitment or removal of these cell plate components were observed. Thus, although PAN1 is localized in cell plates, this study has not revealed its function there. A subtle cell plate formation defect might be revealed via analysis of additional features of cytokinesis in pan mutants