Symmetric cell divisions are boring; they only maintain or expand an existing tissue. The more interesting asymmetric divisions give rise to novel cell types with diverging fates. Two examples during Arabidopsis development have attracted the attention of researchers over the years. The first one marks the entry into the stomatal lineage, when the meristemoid mother cell divides to produce, at the end of the cycle, a pair of guard cells flanked by pavement cells. The second one is the first division of the zygote to differentiate the future globular embryo from the elongated suspensor, a stalk-like structure that supports embryo growth.

Evolution often works by reusing and adapting existing gene networks to new functions. Indeed, the molecular pathways that lead to both of these asymmetrical divisions share many components, from the upstream ERECTA family of membrane receptors to the MAP kinase cascade that includes the MAPKKK YODA and the ubiquitous MPK3 and MPK6. A team lead by Martin Bayer in Tübingen wondered whether the downstream transcription factor SCREAM (SCRM; also known as ICE1) is also shared —and indeed it is, but with an important difference.

对称细胞分裂很无聊;他们只维持或扩大现有的组织。更有趣的不对称分裂产生了具有不同命运的新型细胞类型。多年来，拟南芥开发过程中的两个例子引起了研究人员的注意。第一个标志着进入气孔谱系，此时分生组织母细胞分裂，在周期结束时产生一对侧翼为路面细胞的保卫细胞。第二个是受精卵的第一次分裂，以区分未来的球状胚胎和细长的悬吊，这是一种支持胚胎生长的茎状结构。

进化通常通过重用和适应现有的基因网络以适应新功能来发挥作用。事实上，导致这两种不对称分裂的分子通路共享许多成分，从上游 ERECTA 膜受体家族到包括 MAPKKK YODA 和普遍存在的 MPK3 和 MPK6 的 MAP 激酶级联反应。图宾根的 Martin Bayer 领导的一个团队想知道下游转录因子 SCREAM（SCRM，也称为 ICE1）是否也是共享的，确实是，但有一个重要的区别。