Evolutionary adaptations of the microtubule cytoskeleton during cell division in the land plant lineage

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The colonization of terrestrial habitats by ancestral streptophyte algae approximately 450 Mya ago, followed by the rise of land plants relied on the evolution of novel microtubule cytoskeletal arrays and was accompanied by the diversification and emergence of plant-specific microtubule-associated proteins (MAPs) to adjust cellular processes to novel conditions and interactions. One of the key innovations in plant cytoskeleton organization is the emergence of the preprophase band (PPB)/phragmoplast system. This system facilitates a switch in the mode of cell division from a cleavage-based mechanisms to an inside-out mechanism, in which new cell walls are inserted at the cell center. Functional studies in Arabidopsis thaliana identified networks of eukaryotic and plant-specific MAPs that control the formation of the PPB and phragmoplast. The origin, architecture and dynamics of these complexes, however, are still unknown. Plant-specific IQ67 DOMAIN (IQD) proteins emerged as key regulators of PPB formation and division plane control in Arabidopsis thaliana with proposed functions as hubs in microtubule-associated PPI networks. IQDs share scaffold-like properties, physically interact with known regulators of plant cell division, and are implicated in auxin-dependent control of division plane positioning. Our preliminary data indicate emergence of IQDs early during land plant evolution. We hypothesize that plant-specific IQD scaffolds facilitated the rewiring and acquisition of PPIs at the cytoskeleton to support neo-functionalization and functional specialization during plant cell division and growth regulation. In this project, we aim to identify key principles that govern the adaptations of the microtubule cytoskeleton by investigating the evolution of IQD-assembled PPI networks and their function in cell division. We will approach these aims by functional analyses of IQD functions in the liverwort Marchantia polymorpha and by comparative analyses of microtubule-binding and PPI specificities of IQDs from streptophyte algae, bryophytes, and seed plants.