Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33(rd) Street, Philadelphia, PA 19104, USA.
Department of Physics and Astronomy, University of Tennessee, 1408 Circle Drive, Knoxville, TN 37996, USA.
Cell. 2019 Feb 7;176(4):856-868.e10. doi: 10.1016/j.cell.2019.01.014.
The ornately geometric walls of pollen grains have inspired scientists for decades. We show that the evolved diversity of these patterns is entirely recapitulated by a biophysical model in which an initially uniform polysaccharide layer in the extracellular space, mechanically coupled to the cell membrane, phase separates to a spatially modulated state. Experiments reveal this process occurring in living cells. We observe that in ∼10% of extant species, this phase separation reaches equilibrium during development such that individual pollen grains are identical and perfectly reproducible. About 90% of species undergo an arrest of this process prior to equilibrium such that individual grains are similar but inexact copies. Equilibrium patterns have appeared multiple times during the evolution of seed plants, but selection does not favor these states. This framework for pattern development provides a route to rationalizing the surface textures of other secreted structures, such as cell walls and insect cuticle.
花粉粒的华丽几何壁已经启发了科学家几十年。我们表明，这些图案的进化多样性完全可以通过一个生物物理模型来再现，在该模型中，细胞外空间中最初均匀的多糖层与细胞膜机械耦合并相分离到空间调制状态。实验揭示了这一过程发生在活细胞中。我们观察到，在大约 10%的现存物种中，这种相分离在发育过程中达到平衡，使得每个花粉粒都是相同的并且可以完美重现。大约 90%的物种在达到平衡之前就停止了这个过程，因此每个颗粒都是相似但不完全相同的复制品。在种子植物的进化过程中，平衡模式已经多次出现，但选择并不青睐这些状态。这种模式发展的框架为合理化其他分泌结构（如细胞壁和昆虫表皮）的表面纹理提供了途径。
