Plant cells are surrounded by a rigid cell wall which glues the cells together and fixes their position within a plant tissue. Due to the immobile nature of their cells, plants rely on oriented cell division to construct their overall body plan. The three-dimensional cellular organization of plant tissues therefore represents the outcome of sequential rounds of oriented cell divisions and subsequent interphasic cell elongation. In contrast to animal cells, plant cells determine their plane of division very early during the cell cycle. The first visible sign of division plane determination in somatic plant cells consists of the transformation of the cortical cytoskeletal array into a dense ring of microtubules and actin filaments, termed the preprophase band (PPB), which encircles the premitotic nucleus. The PPB anchors the nucleus, aids bipolar spindle establishment and facilitates the deposition of membrane-attached division zone markers that, in contrast to the transient nature of the PPB, remain present at the plasma membrane throughout mitosis. These markers are assumed to direct the centrifugally expanding cell plate to the correct cortical position where it will ultimately fuse with the parental plasma membrane at the end of cytokinesis, thereby physically separating the two daughter cells.
The mechanism how plant cells execute endocytosis, how somatic cells determine their plane of cell division during both proliferative (symmetric) and formative (asymmetric) divisions, the implications for plant development in case this malfunctions and the role of membrane trafficking in division plane determination are the main biological questions studied in my team. Division plane determination requires the coordinated action of cell cycle progression, cytoskeletal dynamics and endosomal trafficking events. Cytoskeletal dynamicity drives preprophase band formation and breakdown, premitotic nuclear migration and cell plate guidance. Endosomal exo- and endocytic events control the specific composition of the plasma membrane at the cortical division zone and orchestrate the recruitment and dynamic maintenance of cortical division zone markers. The identification of the evolutionary ancient and essential TPLATE endocytic complex in plants puts us in an unprecedented position to unravel the mechanism of endocytosis in plants and its role in division plane determination.
Our cell-biological and live cell imaging-oriented research takes advantage of the available tools in the model plant Arabidopsis thaliana and in the moss Physcomitrella patens, combined with the high spatiotemporal resolving power of imaging tobacco Bright Yellow-2 (BY-2) culture cells as well as Nicotiana benthamiana epidermal leaf pavement cells.