背景回顾：The development of plant roots is subject to control by light. Here, we show that, similar to monotonous root elongation, the periodic induction of lateral roots (LRs) depends on the activation by light of photomorphogenic and photosynthetic photoreceptors in the shoot in a hierarchical order. 

现有假设：The prevailing belief is that the plant hormone auxin serves as a mobile signal transmitter, responsible for interorgan communication, including light-controlled shoot-to-root connections. Alternatively, it has been proposed that the transcription factor HY5 assumes the role as a mobile shoot-to-root signal transmitter. 

主要发现：Here, we provide evidence that photosynthetic sucrose produced in the shoot acts as the long-distance signal carrier regulating the local, tryptophan-based biosynthesis of auxin in the LR generation zone of the primary root tip, where the LR clock controls the pace of LR initiation in an auxin-tunable manner. 

结论：Synchronization of LR formation with primary root elongation allows the adjustment of overall root growth to the photosynthetic performance of the shoot and the maintenance of a constant LR density during light-dark changes in a variable light environment.

植物根的发育受到光的控制。本文中，作者发现与根伸长相似，侧根的诱导依赖于植物地上部中光形态建成和光合作用中光受体的激活。一般认为，植物激素生长素是一种移动信号媒介，负责植物器官间的通信，包括光控制的茎根联结。另外还有一种观点，认为转录因子HY5才是根茎之间的移动信号媒介。本文中，作者通过试验证据表明植物地上部通过光合产生的蔗糖作为长距离信号载体，能够调控主根根尖侧根生成区的、基于色氨酸的局域生长素生物合成，而根时钟通过一个生长素可调的方式控制着侧根起始的速度。侧根形成与主根伸长之间的同步使得植物能够根据地上部的光合表现，调整根的整体生长，从而在一个多变的光环境中根据明暗变化去维持稳定的侧根密度。