Guest Speaker- Jacques Dumais

Abstract: The division of eukaryotic cells involves the assembly of complex cytoskeletal structures. One such structure is the microtubular preprophase band (PPB) observed in dividing plant cells.  The PPB plays a fundamental role in plant development by positioning the phragmoplast and guiding its growth. Moreover, the origin of the PPB in the streptophytes coincides with the rise of more complex meristem structures, suggesting that the PPB may have played a pivotal role in the evolution of land plants.  Despite its importance, it is still not clear how the PPB is formed and positioned within plant cells.  In this talk, I will provide evidence that standard microtubule dynamics and the interaction between microtubules and the cell edges are sufficient to explain the positioning of the PPB.  In the concrete case of the bryophyte Marchantia polymorpha, interphase microtubule arrays reveal many quantitative features typically attributed to the PPB.  Moreover, the self-organization rules elucidated in Marchantia appear to constrain meristem development to only four types of self-replicating apical cells, all of which are observed in land plants.  Finally, I will conclude the talk by revisiting a theme dear to Arthur H Church - the idea that the “beginnings of Botany are in the sea” and that many of the developmental features deemed unique to land plants are in fact natural extensions of cellular processes already present in their most recent algal ancestors.