Division polarity in developing stomata

► Cell polarities must be generated and perceived to initiate asymmetric cell division. ► Cell polarities are generated in response to intrinsic or extrinsic cues. ► The sequence of asymmetric cell divisions that occur in stomatal lineages of Arabidopsis and maize differ. ► The molecules and mechanisms described so far leading to stomatal cell polarities also differ in Arabidopsis and maize. Stomata are generated via asymmetric cell division in both dicots and monocots. Intrinsic or extrinsic polarity cues are perceived and acted upon to generate mother cell polarity and determine asymmetric division planes. Arabidopsis employs both intrinsic and extrinsic cues to orient a variable series of asymmetric stomatal divisions, using novel proteins such as BASL and POLAR to generate polarity. In contrast, maize appears to employ only extrinsic cues to orient the polarities of divisions occurring in an invariant sequence to generate stomatal complexes. Although both plants use receptor-like kinases to generate or orient division polarity in developing stomata, there are few similarities in the proteins and pathway identified to date as regulators of these processes.