Investigating the role of the POLAR gene family in asymmetric cell divisions and epidermis pattern establishment in Brachypodium distachyon

The grass leaf epidermis follows a longitudinal developmental gradient, in which undifferentiated protodermal cells undergo polarity-guided, transverse asymmetric divisions (ACDs) that establish within-file patterning by separating specialised cells and complexes by large pavement cells.

We identified BdPOLAR-like1 (BdPL1) as a key regulator of early ACDs in Brachypodium distachyon. BdPL1 polarises along the apical-basal axis, guiding division plane orientation. BdPL1's ability to guide the division plane was confirmed with misexpression experiments, demonstrating BdPL1’s ability to override native polarity cues of cells with a medio-lateral polarity domain. Correspondingly, loss of BdPL1 disrupted a division plane orientation, leading to pavement cell clustering and patterning defects. Furthermore, live imaging shows that BdPL1’s polarity domain is transient, as it is released from the plasma membrane during cell division.

Taken together, these findings establish BdPL1 as a pre-mitotic regulator of asymmetric cell division, essential at early stages of grass epidermis development.