The Plant Cell Reviews Aspects of Photobiology: It’s a Matter of Stop ’n Go

Where I grew up, traffic lights were quaintly called “stop 'n go lights,” rather than simply “stoplights.” I think most would agree that the ability, eventually, to go forward at a light is as important as the necessity of occasionally stopping. In fact, I have the notion that the local authorities where I live now would do well to pay more attention to the “go” aspect of traffic lights; it seems that many stop cycles are too long, thus effectively encouraging people to run red lights (an alarmingly frequent problem). As with traffic lights, the regulation of biological light signaling is fundamentally a matter of “stop 'n go,” in this case involving the integration of light inputs with other signaling pathways (phytohormones, temperature, and other environmental signals) to regulate the stopping and going of downstream gene expression for optimal growth and development in a continually changing environment. This issue of The Plant Cell includes five review articles covering various aspects of photobiology.

Chew et al. (pages 5–20) summarize computational modeling approaches that have furthered our understanding of complex biological processes in plants, with a focus on those regulated by light. They categorize and present examples of modeling approaches based on the nature of the biological processes under investigation, all of which occur across a vast range of time and space: (1) probing molecular mechanisms; (2) investigating cellular growth, tissue patterning, and organ development; or (3) focusing on growth and developmental events at the organismal level (see figure).

Plant systems span a wide range of spatio-temporal scales. (Adapted from Chew et al. [2014], Figure 1.)

Liscum et al. (pages 38–55) review phototropism, highlighting the complex nature of phototropic responses, involving at least six photoreceptors, multiple auxin receptors and transporters, and integration with other phytohormone signaling pathways to orchestrate plant movement in response to the perception of directional light. Jenkins (pages 21–37) presents an in-depth analysis of the UV-B photoreceptor UVR8, focusing on its physiological role and its structure in relation to the mechanisms of photoreception, signal transduction, and regulation of downstream targets.

Moving farther downstream of light perception, Leivar and Monte (pages 56–78) provide a comprehensive view of phytochrome interacting factors (PIFs) as central integrators of light and other signals. They show how PIFs are emerging as required factors for growth, thanks to their capacity to integrate multiple internal and external signals to optimize plant development. Light is also the principal cue regulating the circadian clock. Seo and Mas (pages 79–87) focus on the diverse posttranslational events that regulate circadian clock function, discussing how plants integrate environmental cues such as light and temperature to maintain circadian homeostasis and generate highly precise waveforms of circadian expression and activity.

This set of reviews offers a great resource for up-to-date summaries and in-depth discussions of our current understanding of these complex networks that integrate plant responses to light with other environmental and developmental cues.