How appendages, such as plant leaves or animal limbs, develop asymmetric shapes remains a fundamental question in biology. Although ongoing research has revealed the genetic regulation of organ pattern formation, how gene activity ultimately directs organ shape remains unclear. Here, we show that leaf dorsoventral (adaxial-abaxial) polarity signals lead to mechanical heterogeneity of the cell wall, related to the methyl-esterification of cell-wall pectins in tomato and Arabidopsis. Numerical simulations predicate that mechanical heterogeneity is sufficient to produce the asymmetry seen in planar leaves. Experimental tests that alter pectin methyl-esterification, and therefore cell wall mechanical properties, support this model and lead to polar changes in gene expression, suggesting the existence of a feedback mechanism for mechanical signals in morphogenesis. Thus, mechanical heterogeneity within tissue may underlie organ shape asymmetry.

中文翻译：

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叶片器官不对称的机械调节。

附属物（例如植物的叶子或动物的肢体）如何形成不对称形状仍然是生物学中的一个基本问题。尽管正在进行的研究已经揭示了器官模式形成的遗传调控，但是基因活性最终如何指导器官形状仍不清楚。在这里，我们显示叶背腹（轴向-背面）极性信号导致细胞壁的机械异质性，与番茄和拟南芥中细胞壁果胶的甲基酯化有关。数值模拟表明，机械异质性足以产生在平面叶片中看到的不对称性。改变果胶甲基酯化从而改变细胞壁机械性能的实验测试支持该模型，并导致基因表达发生极性变化，提示在形态发生中存在机械信号的反馈机制。因此，组织内的机械异质性可能是器官形状不对称的基础。