背景回顾：A key aim in biology is to identify which genetic changes contributed to the evolution of form through time. Apical dominance, the inhibitory effect exerted by shoot apices on the initiation or outgrowth of distant lateral buds, is a major regulatory mechanism of plant form. Nearly a century of studies in the sporophyte of flowering plants have established the phytohormone auxin as a front-runner in the search for key factors controlling apical dominance, identifying critical roles for long-range polar auxin transport and local auxin biosynthesis in modulating shoot branching. 

提出问题：A capacity for lateral branching evolved by convergence in the gametophytic shoot of mosses and primed its diversification; however, polar auxin transport is relatively unimportant in this developmental process, the contribution of auxin biosynthesis genes has not been assessed, and more generally, the extent of conservation in apical dominance regulation within the land plants remains largely unknown. 

主要发现：To fill this knowledge gap, we sought to identify genetic determinants of apical dominance in the moss Physcomitrium patens. 

结果1-组学指示生长素作用：Here, we show that leafy shoot apex decapitation releases apical dominance through massive and rapid transcriptional reprogramming of auxin-responsive genes and altering auxin biosynthesis gene activity. 

结果2-TAR-YUC模块：We pinpoint a subset of P. patens TRYPTOPHAN AMINO-TRANSFERASE (TAR) and YUCCA FLAVIN MONOOXYGENASE-LIKE (YUC) auxin biosynthesis genes expressed in the main and lateral shoot apices and show that they are essential for coordinating branch initiation and outgrowth.

结论：Our results demonstrate that local auxin biosynthesis acts as a pivotal regulator of apical dominance in moss and constitutes a shared mechanism underpinning shoot architecture control in land plants.

生物学的一个关键目标是鉴定哪些遗传上的改变塑造了随着时间而发生的形态演化。顶端优势是指植物茎尖对远端侧芽起始或向外生长的抑制作用，是植物形态的一个重要调控机制。对于有花植物的孢子体将近一个世纪的研究，建立了生长素作为最关键的植物激素，用作搜寻控制顶端优势的核心因子、鉴定长距离极性生长素运输及局域生长素合成在控制茎分枝中的关键作用。苔藓配子体茎的趋同演化获得了侧生分枝的能力，开启了其多样化；但是，该发育过程中生长素的极性运输相对来说并不是十分重要，且不清楚生长素生物合成基因在该发育过程中的作用，更广地说，对于顶端优势的调控机制在陆地植物中的保守性程度仍缺乏认知。为了填补这一知识空白，本文中作者鉴定了苔藓植物小立碗藓中控制顶端优势的遗传决定因子。作者发现，通过对小立碗藓叶状茎顶端的去顶处理，会通过快速转录重编程大量生长素响应基因及改变生长素生物合成基因活性来释放顶端优势。作者鉴定到了一个在主茎和侧生茎顶端表达的TAR-YUC生长素合成基因模块，并发现该模块对于协调小立碗藓的侧枝起始和向外生长方面是必需的。本文的结果揭示了在小立碗藓中，局域性生长素生物合成是调控顶端优势的重要因子，这也构成了陆地植物茎结构的共享调控机制。