Light signaling, root development and plasticity

Light is the energy source for plants as it drives photosynthesis to produce sugars. Given the obvious fact that light mostly occurs aboveground and not in the soil, most interactions of plants with light have been studied in shoot parts of the plant. Research over more than a century has yielded tremendous insights into how light not only drives photosynthesis, but also acts as an environmental cue that informs plants about their environment. Light quality and duration for example, drive major developmental changes such as photomorphogenesis, photoperiodic induction of flowering, phototropism, and shade avoidance (see for example the following recent reviews: (Wu, 2014; Fankhauser and Christie, 2015; Xu et al., 2015; Ballaré and Pierik, 2017). The picture that has emerged is that plants have very detailed light signaling mechanisms, with photoreceptors dedicated to different wavelengths in the light spectrum and interactions between these photoreceptors themselves and their downstream signal transduction pathways.
Studies have accumulated over the past 15 years, and intensified in recent years showing pronounced effects of light on root physiology and development. Although some effects of light availability on root growth will be the simple consequence of differential sugar availability to the roots due to photosynthesis in the shoot, there is substantial evidence for more sophisticated signaling impacts of different aspects of the light environment.
In this Update, we will briefly review the core light signaling mechanisms, their impact on root development and plasticity and the functional implications of these above-belowground interactions.