Pollen cell walls form from modulated phases

Pollen cell walls exhibit a huge diversity of morphologies including ordered and disordered arrangements of spikes, stripes, and holes. Electron microscopy images of pollen wall development across the spermatophyte tree reveal that a ubiquitous material called primexine, thought to be made of a mixture of polysaccharides, lipoproteins and glycoproteins, templates these morphologies. Recently, our imaging studies identified that a phase separation of primexine coupled to the cell membrane induces a phase transition to modulated phases which pattern the pollen wall. We formulated a Landau-Ginzburg free energy description of this process in which we treat the primexine concentration as a scalar field coupled to the cell membrane and calculated the equilibrium states. We also studied the dynamics of our model and found that together kinetically-arrested and equilibrium states recapitulate most extant cell morphologies. Further imaging studies indicate that nanoscale patterns form within the phase-separated domains, thus we additionally model the lyotropic liquid crystalline-like phases employing self-consistent field theory simulations. Finally, we completed an evolutionary analysis in which character traits are defined by parameters of our model that reveals while equilibrium patterns have appeared multiple times during evolution, selection does not favor these states.