Cell polarization is a fundamental feature of all cellular organisms and provides one of the major mechanisms to regulate stem cell asymmetric cell division (ACD). In plants, the stomatal lineage cells represent a population of dispersed stem cells and their asymmetric division requires a polarized plant-specific, non-membrane protein BASL (BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE). Our past work established a positive feedback loop between BASL and the YODA MAPK cassette to constitute a polarity complex at the cell cortex of stomatal lineage cells and contributes to the cell fate differentiation. At the conference, I will introduce one BASL-interacting protein family for their function in the regulation of stomatal ACD. Members of this Ser/Thr protein phosphatase family appeared to polarize at a specific time point to control cell-fate determination. I will explain the possible mechanisms for these phosphatases to coordinate both cell division and cell fate determination, the two seemingly opposing processes in stomatal ACD in plants.