Ectopic BASL reveals tissue cell polarity throughout leaf development in Arabidopsis thaliana

Signals determining tissue polarity are fundamental to proper organ development. Asymmetry across the entire organ  arises due to to polarity fields. Although there are numerous examples of proteins that express preferential polar localization in the cell, the mechanism that coordinates the polarity field across the whole organ level is still unknown. Mansfield et al. used ectopically expressed BREAKING OF ASYMETRY IN THE STOMATAL LINEAGE (BASL) as a reporter to examine whether the polarity field is dependent on stomatal development. The authors observed asymmetrical BASL localization toward the proximal single lobe. This asymmetric localization was similar in speechless mutant as well as in wild-type plants, suggesting that polarity field is not affected by stomatal development. Cell shape anisotropy, auxin inhibitors or microtubule destabilizing agents did not alter leaf polarity, as reported by BASL. Interestingly, BASL localization was complementary to the PIN1 in developing leaf primodia. In future studies, the newly identified identified proximodistal polarity field might provide an insight into the mechanisms regulating asymmetric organ development. (Summary by Magdalena Julkowska) Curr. Biol. 10.1016/j.cub.2018.06.019