背景回顾：Asymmetric and oriented stem cell divisions enable the continued production of patterned tissues. The molecules that guide these divisions include several “polarity proteins” that are localized to discrete plasma membrane domains, are differentially inherited during asymmetric divisions, and whose scaffolding activities can guide division plane orientation and subsequent cell fates. In the stomatal lineages on the surfaces of plant leaves, asymmetric and oriented divisions create distinct cell types in physiologically optimized patterns. 

提出问题：The polarity protein BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) is a major regulator of stomatal lineage division and cell fate asymmetries in Arabidopsis, but its role in the stomatal lineages of other plants is unclear. 

主要发现：Here, using phylogenetic and functional assays, we demonstrate that BASL is a eudicot-specific polarity protein.

结果1-双子叶BASL：Dicot BASL orthologs can polarize in heterologous systems and rescue the Arabidopsis BASL mutant. 

结果2-其它进化枝的BASL-like：The more widely distributed BASL-like proteins, although they share BASL’s conserved C-terminal domain, are neither polarized nor do they function in asymmetric divisions of the stomatal lineage. 

结果3-拟南芥vs番茄：Comparison of BASL protein localization and loss of function BASL phenotypes in Arabidopsis and tomato revealed previously unappreciated differences in how asymmetric cell divisions are employed for pattern formation in different species. 

结论：This multi-species analysis therefore provides insight into the evolution of a unique polarity regulator and into the developmental choices available to cells as they build and pattern tissues.

 摘 要 

不对称的和定向的干细胞分裂能够保证组织模式建成的连续性。指导这些不对称的和定向分裂的分子包括几个定位于离散质膜域上的极性蛋白，并且在不对称分裂后会差异性的继承给子细胞，其支架活性能够指导分裂板的方向以及后续的细胞命运。在植物叶片表面的气孔细胞谱系中，不对称和定向的分裂创造了不同的细胞类群，各自具有生理最优模式。极性蛋白BASL是调控拟南芥气孔谱系不对称分裂和细胞命运不对称性的主要调节子，但是其在其它植物气孔谱系中的作用还不清楚。本文中，作者通过系统发育和功能实验发现，BASL是一个真双子叶植物特异的极性蛋白。双子叶BASL同源物能够在异源系统中极性化，并拯救拟南芥BASL基因功能缺失突变体的表型。而其他类群的BASL-like 蛋白，尽管它们具有BASL保守的C端结构域，但是要么不能极性化，要么不能作用于气孔谱系的不对称分裂。通过比较拟南芥和番茄中的BASL蛋白定位和BASL基因功能缺失的表型揭示了不对称细胞分裂的差异性如何作用于不同物种的模式建成，这一点在先前的研究中未受到重视。本文的研究结果为BASL这一极性蛋白的演化提供了新的视野，同时也为细胞中可用来建成和塑造组织模式的发育选择提供了新的见解。