Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
Curr Biol. 2009 Sep 15;19(17):1485-90. doi: 10.1016/j.cub.2009.06.070. Epub 2009 Jul 30.
Development of seed plant embryos is polarized along the apical-basal axis. This polarization occurs in the absence of cell migration and culminates in the establishment of two distinct pluripotent cell populations: the shoot apical meristem (SAM) and root meristem (RM), which postembryonically give rise to the entire shoot and root systems of the plant. The acquisition of genetic pathways that delimit root from shoot during embryogenesis must have played a pivotal role during land plant evolution because roots evolved after shoots in ancestral vascular plants and may be shoot-derived organs. However, such pathways are very poorly understood. Here we show that RM establishment in the model plant Arabidopsis thaliana requires apical confinement of the Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) proteins PHABULOSA (PHB) and PHAVOLUTA (PHV), which direct both SAM development and shoot lateral organ polarity. Failure to restrict PHB and PHV expression apically via a microRNA-dependent pathway prevents correct elaboration of the embryonic root development program and results in embryo lethality. As such, repression of a fundamental shoot development pathway is essential for correct root development. Additionally, our data suggest that a single patterning process, based on HD-ZIP III repression, mediates both apical-basal and radial polarity in the embryo and lateral organ polarity in the shoot.
种子植物胚胎的发育沿着顶端-基轴方向极化。这种极化发生在没有细胞迁移的情况下，并最终导致两个不同的多能细胞群体的建立：茎尖分生组织（SAM）和根分生组织（RM），它们在后胚胎期产生植物的整个茎和根系统。在胚胎发生过程中，限定根和茎的遗传途径的获得，在陆地植物进化过程中一定起到了关键作用，因为根在祖先维管植物中比茎进化得晚，并且可能是茎衍生的器官。然而，这些途径还非常不清楚。在这里，我们表明，拟南芥模式植物中 RM 的建立需要 Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) 蛋白 PHABULOSA (PHB) 和 PHAVOLUTA (PHV) 的顶端限制，这些蛋白指导 SAM 的发育和茎侧生器官的极性。通过 microRNA 依赖性途径不能将 PHB 和 PHV 的表达限制在顶端，会阻止胚胎根发育程序的正确细化，并导致胚胎致死。因此，对基本的茎发育途径的抑制对于正确的根发育是必不可少的。此外，我们的数据表明，基于 HD-ZIP III 抑制的单个模式形成过程，介导胚胎中的顶端-基轴和径向极性以及茎中的侧生器官极性。
