KATANIN is required for the formation of complete preprophase bands and subsequent division positioning in two asymmetric divisions of the maize stomatal complex.

Microtubule dynamics underpin cell division, movement, and growth in eukaryotic organisms. KATANIN p60 is a microtubule-severing protein that promotes proper cell elongation and division. In plants, division positioning is initiated in late G2 via the formation of a microtubule structure called the preprophase band (PPB). Maize p60 mutants have defects in microtubule severing and form abnormal PPBs in symmetrically dividing cells, including both incompletely assembled and misoriented PPBs. Here, we show that two types of asymmetric divisions required to generate stomatal complexes in maize p60 mutants have normally positioned but often incompletely formed PPBs. Incompletely formed PPBs lead to misoriented divisions and nuclear positioning defects in p60 mutants.