A polarized nuclear position is required for correct division plane specification during maize stomatal development

Abstract

Asymmetric cell division generates new cell types and is a feature of development in multicellular organisms. Prior to asymmetric cell division, cell polarity is established. Zea mays stomatal development serves as an excellent plant model system for asymmetric cell division, especially the asymmetric division of the subsidiary mother cell (SMC). In SMCs, the nucleus migrates to a polar location after the accumulation of polarly localized proteins, but before the appearance of the preprophase band. We examined a mutant of the outer nuclear membrane protein, which is part of the LINC (linker of nucleoskeleton and cytoskeleton) complex that localizes to the nuclear envelope in interphase cells. Previously, mlks2 (maize linc kash sine-like2) was observed to have abnormal stomata. We confirmed and identified the precise defects that lead to abnormal asymmetric divisions. Proteins that are polarly localized in SMCs prior to division polarize normally in mlks2. However, polar localization of the nucleus is sometimes impaired, even in cells that have otherwise normal polarity. This leads to a misplaced preprophase band and atypical division planes. MLKS2 is localized to mitotic structures, however the structure of the preprophase band, spindle and phragmoplast appeared normal in mlks2. Timelapse imaging revealed that mlks2 has defects in pre-mitotic nuclear migration towards the polarized site, and unstable position at the division site after formation of the preprophase band. We show that nuclear envelope proteins promote pre-mitotic nuclear migration and stable nuclear position, and that the position of the nucleus influences division plane establishment in asymmetrically dividing cells. One-sentence summaryNuclear movement and positioning prior to asymmetric cell division is required for deciding the future division site.