背景回顾：Root meristem organization is maintained by an interplay between hormone signaling pathways that both interpret and determine their accumulation and distribution. The interacting hormones Brassinosteroids (BR) and auxin control the number of meristematic cells in the Arabidopsis root. BR was reported both to promote auxin signaling input and to repress auxin signaling output. 

提出问题：Whether these contradicting molecular outcomes co-occur and what their significance in meristem function is remain unclear.

主要发现：Here, we established a dual effect of BR on auxin, with BR simultaneously promoting auxin biosynthesis and repressing auxin transcriptional output, which is essential for meristem maintenance. 

结果1：Blocking BR-induced auxin synthesis resulted in rapid BR-mediated meristem loss. Conversely, plants with reduced BR levels were resistant to a critical loss of auxin biosynthesis, maintaining their meristem morphology.

结果2：In agreement, injured root meristems, which rely solely on local auxin synthesis, regenerated when both auxin and BR synthesis were inhibited.

结果3：Use of BIN2 as a tool to selectively inhibit BR signaling yielded meristems with distinct phenotypes depending on the perturbed tissue: meristem reminiscent either of BR-deficient mutants or of high BR exposure. This enabled mapping of the BR-auxin interaction that maintains the meristem to the outer epidermis and lateral root cap tissues and demonstrated the essentiality of BR signaling in these tissues for meristem response to BR. BR activity in internal tissues however, proved necessary to control BR levels.

结论：Together, we demonstrate a basis for inter-tissue coordination and how a critical ratio between these hormones determines the meristematic state.

 摘 要 

根分生组织是由两个能够决定分生组织积累和分布的激素信号转导通路间的互作来维持的。油菜素内酯BR和生长素之间的互作控制了拟南芥根组织中分生细胞的数量。BR能够促进生长素信号转导的输入和抑制生长素信号转导的输出。而这种相互矛盾的分子结果是否同时发生，以及它们在分生组织功能中的意义尚不清楚。本文中，作者揭示了BR对于生长素的双向作用，BR同时促进生长素合成和抑制生长素的转录输出，这对于分生组织的维持是必须的。阻断BR诱导的生长素合成，会导致BR介导的分生组织快速丢失。相反，降低BR水平能够帮助植株抵抗生长素生物合成的严重损失，以维持其分生组织的形态。同样，当生长素和BR合成均受到抑制时，仅依赖于局部生长素合成的根损伤分生组织能够再生。利用BIN2来选择性抑制BR信号，会根据受干扰的组织类型产生不同表型的分生组织，类似于BR缺陷突变体或高水平BR处理。这使得作者能够探究BR和生长素之间的互作，作用于维持分生组织到外表皮和侧根冠组织，并证明了这些组织中BR信号转导对于分生组织对BR响应的重要性。然而，内部组织中的BR活性被证明是控制BR水平所必需的。综上，本文的研究证明了组织间协调的基础，以及激素间的临界比率如何决定分生组织状态。