Abstract
Light is among the most important exogenous factors that regulate plant development. To sense light quality, intensity, direction, and duration, plants have evolved multiple photoreceptors that enable the detection of photons from the ultraviolet B (UV-B) to the far-red spectrum. To study the effect of different light qualities on early gene expression, dark-grown Arabidopsis (Arabidopsis thaliana) seedlings were either irradiated with continuous far-red, red, or blue light or received pulses of red, UV-A, or UV-A/B light. The expression profiles of seedlings harvested at 45 min and 4 h were determined on a full genome level and compared with the profiles of dark controls. Data were used to identify light-regulated genes and to group these genes according to their light responses. While most of the genes were regulated by more than one light quality, a considerable number of UV-B-specific gene expression responses were obtained. An extraordinarily high similarity in gene expression patterns was obtained for samples that perceived continuous irradiation with either far-red or blue light for 4 h. Mutant analyses hint that this coincidence is caused by a convergence of the signaling cascades that regulate gene expression downstream of cryptochrome blue light photoreceptors and phytochrome A. Whereas many early light-regulated genes exhibited uniform responses to all applied light treatments, highly divergent expression patterns developed at 4 h. These data clearly indicate that light signaling during early deetiolation undergoes a switch from a rapid, but unspecific, response mode to regulatory systems that measure the spectral composition and duration of incident light.
Highlights
Light is among the most important exogenous factors that regulate plant development
To reveal gene expression patterns at the initial light response during seedling deetiolation, 4-d-old, darkgrown wild-type Arabidopsis seedlings were treated with Continuous far-red light (cFR), continuous red light (cR), or continuous blue light (cB) or received pulse of red light (pR), pulse treatments with UV-A (pUV-A), or pUVA/B before transfer back to darkness
High values were only detected within the three biological replicates of individual light treatments and between the 4-h pR and pUV-A samples. These results clearly indicate that, first, cFR and cB coregulate a common set of genes during later stages of Arabidopsis seedling deetiolation and, second, the effect of these two light qualities on gene expression differs from other light treatments
Summary
Light is among the most important exogenous factors that regulate plant development. To sense light quality, intensity, direction, and duration, plants have evolved multiple photoreceptors that enable the detection of photons from the ultraviolet B (UV-B) to the far-red spectrum. Intensity, direction, and duration, higher plants have evolved with many families of photoreceptors that cumulatively absorb photons from the UV-B to the far-red spectrum of sunlight (Franklin et al, 2005; Christie, 2007; Li and Yang, 2007; Demarsy and Fankhauser, 2009; Jenkins, 2009; Franklin and Quail, 2010). Physiological and molecular approaches give additional hints for the existence of UV-B receptors (Jenkins, 2009) Together, these photoreceptors control the timing and extent of many developmental transitions, including seed germination, seedling deetiolation, phototropism, shade avoidance responses, circadian rhythms, and flowering time (Chen et al, 2004; Franklin et al, 2005; Franklin and Quail, 2010). It is known that phyA can function as a blue light photoreceptor (Casal and Mazzella, 1998; Neff and Chory, 1998; Poppe et al, 1998)
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