DELLAs Contribute to Plant Photomorphogenesis

Abstract

Plant morphogenesis is profoundly influenced by light (a phenomenon known as photomorphogenesis). For example, light inhibits seedling hypocotyl growth via activation of phytochromes and additional photoreceptors. Subsequently, information is transmitted through photoreceptor-linked signal transduction pathways and used (via previously unknown mechanisms) to control hypocotyl growth. Here we show that light inhibition of Arabidopsis (Arabidopsis thaliana) hypocotyl growth is in part dependent on the DELLAs (a family of nuclear growth-restraining proteins that mediate the effect of the phytohormone gibberellin [GA] on growth). We show that light inhibition of growth is reduced in DELLA-deficient mutant hypocotyls. We also show that light activation of phytochromes promotes the accumulation of DELLAs. A green fluorescent protein (GFP)-tagged DELLA (GFP-RGA) accumulates in elongating cells of light-grown, but not dark-grown, transgenic wild-type hypocotyls. Furthermore, transfer of seedlings from light to dark (or vice versa) results in rapid changes in hypocotyl GFP-RGA accumulation, changes that are paralleled by rapid alterations in the abundance in hypocotyls of transcripts encoding enzymes of GA metabolism. These observations suggest that light-dependent changes in hypocotyl GFP-RGA accumulation are a consequence of light-dependent changes in bioactive GA level. Finally, we show that GFP accumulation and quantitative modulation of hypocotyl growth is proportionate with light energy dose (the product of exposure duration and fluence rate). Hence, DELLAs inhibit hypocotyl growth during the light phase of the day-night cycle via a mechanism that is quantitatively responsive to natural light variability. We conclude that DELLAs are a major component of the adaptively significant mechanism via which light regulates plant growth during photomorphogenesis.

Strigolactones as mediators of plant growth responses to environmental conditions

“…61), whereas both gibberellins and brassinosteroids have been shown to be involved in dark-light transition and photomorphogenesis (i.e., influence of light on plant morphogenesis), demonstrated for hypocotyl growth and elongation. 62,63 With respect to nutrient response, auxin, cytokinin, ethylene, gibberellins and abscisic acid have been shown to affect root and shoot development in response to nutrient conditions; conversely, mineral nutrient conditions have been shown to influence hormone biosynthesis, transport and signaling (reviewed in ref. 20, 24 and 64).…”

A molecular framework for light and gibberellin control of cell elongation

“…Gibberellins (GAs) exert an opposite effect to light on photomorphogenesis 2 . GAs promote etiolated growth, whereas GA-deficiency induces a partially de-etiolated phenotype in the dark, which is reverted by a lack of DELLA function 2,9 . DELLAs function as key repressors of GA-responsive growth, by inhibiting GA-regulated gene expression 5 .…”

Large-Scale Identification of Gibberellin-Related Transcription Factors Defines Group VII ETHYLENE RESPONSE FACTORS as Functional DELLA Partners

“…For this, we took advantage of the TRANSPLANTA (TPT) collection of Arabidopsis lines for conditional TF overexpression under the regulation of a b-estradiol-inducible promoter (Coego et al, 2014). It has been reported that GAs promote skotomorphogenesis, such that etiolated seedlings growing under GA-limiting conditions display photomorphogenic traits, such as short hypocotyls, an open apical hook, and unfolded cotyledons (Alabadí et al, 2004(Alabadí et al, , 2008Achard et al, 2007b;Gallego-Bartolomé et al, 2011). We screened 641 TPT lines representing 276 TFs growing in darkness under two different conditions: 10 nM GA biosynthesis inhibitor paclobutrazol (PAC) with 5 mM b-estradiol for 3 d to score their apical hook angle and 1 mM PAC with 5 mM b-estradiol for 7 d to score the angle between cotyledons.…”

“…The GA metabolic pathway is responsive to environmental factors both biotic and abiotic (Achard et al, 2006(Achard et al, , 2007a(Achard et al, , 2007bZhao et al, 2007;Alabadí et al, 2008;Navarro et al, 2008;Stavang et al, 2009). Moreover, the GA pathway is also modulated by endogenous factors, such as the circadian clock , as well as other hormones, including auxins, ethylene, or cytokinins (Jasinski et al, 2005;Frigerio et al, 2006;Achard et al, 2007a).…”