背景回顾：Growth regulation tailors development in plants to their environment. A prominent example of this is the response to gravity, in which shoots bend up and roots bend down. 

提出问题：This paradox is based on opposite effects of the phytohormone auxin, which promotescell expansion in shoots while inhibiting it in roots via a yet unknown cellular mechanism. 

主要发现：Here, by combining microfluidics, live imaging, genetic engineering and phosphoproteomics in Arabidopsis thaliana, we advance understanding of how auxin inhibits root growth. 

结果：We show that auxin activates two distinct, antagonistically acting signalling pathways that converge on rapid regulation of apoplastic pH, a causative determinant of growth. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H+-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H+ influx, causing apoplast alkalinization. 

结论：Simultaneous activation of these two counteracting mechanisms poises roots for rapid, fine-tuned growth modulation in navigating complex soil environments.

 摘 要 

生长调控使植物能够适应周边环境调整发育进程。一个突出的例子就是植物对于重力的响应，即地上部分的组织向上弯曲生长，而地下部分的组织则向下弯曲生长。这一悖论基于植物激素生长素的相反作用，生长素通过一个未知的细胞机制促进地上组织中的细胞扩展，但抑制根中的细胞扩展。本文中，作者通过结合拟南芥的微流体、实时成像、基因工程和磷酸蛋白质组学，进一步了解了生长素如何抑制根系的生长。作者的研究表明，生长素激活两种不同的、具有拮抗作用的信号转导通路，这些通路最终收敛于生长决定因素质外体pH的快速调节。基于细胞表面的跨膜激酶TMK1与质膜H⁺-ATP酶相互作用，并介导其的磷酸化和活化，从而导致质外体的酸化；而细胞内经典的生长素信号转导会促进细胞H⁺内流，导致质外体碱化。这两种相互抵消机制的同时被激活，从而使得植物根系在复杂土壤环境中被快速、精细地调节生长。