Dancing in the dark: darkness as a signal in plants

Abstract

Daily cycles of light and dark provide an organizing principle and temporal constraints under which life on Earth evolved. While light is often the focus of plant studies, it is only half the story. Plants continuously adjust to their surroundings, taking both dawn and dusk as cues to organize their growth, development and metabolism to appropriate times of day. In this review, we examine the effects of darkness on plant physiology and growth. We describe the similarities and differences between seedlings grown in the dark versus those grown in light–dark cycles, and the evolution of etiolated growth. We discuss the integration of the circadian clock into other processes, looking carefully at the points of contact between clock genes and growth-promoting gene-regulatory networks in temporal gating of growth. We also examine daily starch accumulation and degradation, and the possible contribution of dark-specific metabolic controls in regulating energy and growth. Examining these studies together reveals a complex and continuous balancing act, with many signals, dark included, contributing information and guiding the plant through its life cycle. The extraordinary interconnection between light and dark is manifest during cycles of day and night and during seedling emergence above versus below the soil surface.

PIF3 is a negative regulator of the CBF pathway and freezing tolerance in Arabidopsis

“…It was shown that PIF3 promotes hypocotyl growth during the night (38,42), whereas the CBF pathway represses plant growth by promoting the accumulation of DELLAs (43,44). We speculate that PIF3-mediated repression of CBF genes in darkness at warm temperatures not only relieves the repressive effect of the CBF pathway on plant growth, but also limits the amount of valuable resources that are channeled into freezing tolerance when it is not essential.…”

DET1-mediated degradation of a SAGA-like deubiquitination module controls H2Bub homeostasis

“…Photomorphogenesis is a developmental switch that initiates upon the first perception of light by young plants reaching the soil surface. This transition triggers the launching of organ growth and the establishment of photosynthesis, most notably through the differentiation of primary leaf (cotyledon) cells (reviewed in (Casal, 2013;Seluzicki et al, 2017;Wu, 2014). The process involves changes at transcriptomic, epigenomic and nuclear architecture levels (Bourbousse et al, 2015;Charron et al, 2009;Sullivan et al, 2014).…”

Seedling Establishment: A Dimmer Switch-Regulated Process between Dark and Light Signaling

“…Finally, we discuss some of the challenges faced by young seedlings during their establishment, such as variations in temperature or in light quality and quantity. Although mentioned briefly, we do not cover in detail the contribution of sugars or temperature to seedling establishment in response to dark and light signals; we refer readers to excellent recent reviews Legris et al, 2017;Seluzicki et al, 2017). The emerging view is that of seedling establishment regulated as a dimmer-type switch where relative amounts of dark and light signaling dynamically optimize plant development to the surrounding light environment.…”