PAN1: a receptor-like protein that promotes polarization of an asymmetric cell division in maize.

Polarization of cell division is essential for eukaryotic development, but little is known about how this is accomplished in plants. The formation of stomatal complexes in maize involves the polarization of asymmetric subsidiary mother cell (SMC) divisions toward the adjacent guard mother cell (GMC), apparently under the influence of a GMC-derived signal. We found that the maize pan1 gene promotes the premitotic polarization of SMCs and encodes a leucine-rich repeat receptor-like protein that becomes localized in SMCs at sites of GMC contact. PAN1 has an inactive kinase domain but is required for the accumulation of a membrane-associated phosphoprotein, suggesting a function for PAN1 in signal transduction. Our findings implicate PAN1 in the transmission of an extrinsic signal that polarizes asymmetric SMC divisions toward GMCs.