Mp regulates air pore complex development in the liverwort .

The colonisation of the land by plants was accompanied by the evolution of complex tissues and multicellular structures comprising different cell types as morphological adaptations to the terrestrial environment. Here, we show that the single WIP protein in the early-diverging land plant L. is required for the development of the multicellular gas exchange structure: the air pore complex. This 16-cell barrel-shaped structure surrounds an opening between epidermal cells that facilitates the exchange of gases between the chamber containing the photosynthetic cells inside the plant and the air outside. Mp is expressed in cells of the developing air pore complex and the morphogenesis of the complex is defective in plants with reduced Mp function. The role of WIP proteins in the control of different multicellular structures in and the flowering plant suggests that these proteins controlled the development of multicellular structures in the common ancestor of land plants. We hypothesise that genes were subsequently co-opted in the control of morphogenesis of novel multicellular structures that evolved during the diversification of land plants.