Green Light Adjusts the Plastid Transcriptome during Early Photomorphogenic Development

Abstract

During the transition from darkness to light, a suite of light sensors guides gene expression, biochemistry, and morphology to optimize acclimation to the new environment. Ultraviolet, blue, red, and far-red light all have demonstrated roles in modulating light responses, such as changes in gene expression and suppression of stem growth rate. However, green wavebands induce stem growth elongation, a response not likely mediated by known photosensors. In this study, etiolated Arabidopsis (Arabidopsis thaliana) seedlings were treated with a short, dim, single pulse of green light comparable in fluence and duration to that previously shown to excite robust stem elongation. Genome microarrays were then used to monitor coincident changes in gene expression. As anticipated, phytochrome A-regulated, nuclear-encoded transcripts were induced, confirming proper function of the sensitive phytochrome system. In addition, a suite of plastid-encoded transcripts decreased in abundance, including several typically upregulated after phytochrome and/or cryptochrome activation. Further analyses using RNA gel-blot experiments demonstrated that the response is specific to green light, fluence dependent, and detectable within 30 min. The response obeys reciprocity and persists in the absence of known photosensors. Plastid transcript down-regulation was also observed in tobacco (Nicotiana tabacum) with similar temporal and fluence-response kinetics. Together, the down-regulation of plastid transcripts and increase in stem growth rate represent a mechanism that tempers progression of early commitment to the light environment, helping tailor seedling development during the critical process of establishment.

Contributions of green light to plant growth and development

“…Green light also induces transcriptional profi le changes. Microarray analyses based on the early stem kinetics reported by Folta (2004) show that many of the transcripts upregulated by green light are identical to those induced by phyA ( Dhingra et al, 2006 ). This observation is not surprising since phyA is extremely sensitive and abundant in the dark-grown seedling.…”

“…The phot receptors, while unlikely receptors for pure green light ( Kennis et al, 2003 ), are profoundly sensitive, and minor blue light remnants of a green-enriched canopy are also likely highly informative ( Wang et al, 2012 ). There are green responses that cannot be accounted for genetically ( Folta, 2004 ;Dhingra et al, 2006 ;Zhang et al, 2011 ). They persist in multiple null photoreceptor backgrounds and typically operate in the opposite direction to normal light responses.…”

Green Light Induces Shade Avoidance Symptoms

“…Green light responses are either cryptochrome dependent (Banerjee et al, 2007;Bouly et al, 2007) or persist in all mutant backgrounds tested, suggesting an unknown receptor (Folta, 2004;Dhingra et al, 2006). To test if the morphological changes observed are mediated by a known class of light sensors, the experiments in Figure 1 were repeated using cryptochrome (cry) and phytochrome (phy) mutant plants.…”

“…Other green light effects are independent of known sensory systems. Green light induces transient stem elongation in the etiolated seedling (Folta, 2004) and also drives a decrease in steady-state transcript accumulation of various plastid transcripts (Dhingra et al, 2006). Whether cryptochrome dependent or cryptochrome independent, either mechanism describes the effects of green wavebands that oppose blue light responses.…”

Phytochrome-mediated light signaling in plants: emerging trends

“…There are also reports substantiating many green-light (GL)-mediated responses in plants and, consequently, there are speculations for the occurrence of even a zeaxanthin-based compound as a green light receptor (Frechilla et al, 2000;Talbott et al, 2003;Folta, 2004;Dhingra et al, 2006;Folta and Maruhnich, 2007).…”