Seedling establishment : a a dimmer switch-regulated process between dark and light signaling

By being exquisitely sensitive to their light surroundings, plants are able to continuously adjust their growth to optimize fitness. Darkness is an important cue for plants and a time when they actively grow and develop through regulation of the appropriate gene networks and biochemical changes. Although plants might not possess "dark receptors," inactive photoreceptors facilitate activation and inhibition of dark-specific processes, and thus darkness itself might be considered a signal triggering a myriad of responses. In this Update, we review the effects of dark and light signaling during seedling establishment. We describe the features of seedlings germinated in the dark and their switch in development upon emerging into the light. We examine how aboveground growth is regulated by the duration of dark/light cycles and how circadian clock signaling is integrated. 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 (Franklin et al., 2014; 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

GENOMES UNCOUPLED1-independent retrograde signaling targets the ethylene pathway to repress photomorphogenesis

Altres ajuts: CERCA Programme/Generalitat de CatalunyaWhen germinating in the light, Arabidopsis (Arabidopsis thaliana) seedlings undergo photomorphogenic development, characterized by short hypocotyls, greening, and expanded cotyledons. Stressed chloroplasts emit retrograde signals to the nucleus that induce developmental responses and repress photomorphogenesis. The nuclear targets of these retrograde signals are not yet fully known. Here, we show that lincomycin-treated seedlings (which lack developed chloroplasts) show strong phenotypic similarities to seedlings treated with ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid, as both signals inhibit cotyledon separation in the light. We show that the lincomycin-induced phenotype partly requires a functioning ET signaling pathway, but could not detect increased ET emissions in response to the lincomycin treatment. The two treatments show overlap in upregulated gene transcripts, downstream of transcription factors ETHYLENE INSENSITIVE3 and EIN3-LIKE1. The induction of the ET signaling pathway is triggered by an unknown retrograde signal acting independently of GENOMES UNCOUPLED1. Our data show how two apparently different stress responses converge to optimize photomorphogenesis

Circadian waves of transcriptional repression shape PIF-regulated photoperiod-responsive growth in a<i>rabidopsis</i>

Plants coordinate their growth and development with the environment through integration of circadian clock and photosensory pathways. In Arabidopsis thaliana, rhythmic hypocotyl elongation in short days (SD) is enhanced at dawn by the basic-helix-loop-helix (bHLH) transcription factors PHYTOCHROME-INTERACTING FACTORS (PIFs) directly inducing expression of growth-related genes [1-6]. PIFs accumulate progressively during the night and are targeted for degradation by active phytochromes in the light, when growth is reduced. Although PIF proteins are also detected during the day hours [7-10], their growth-promoting activity is inhibited through unknown mechanisms. Recently, the core clock components and transcriptional repressors PSEUDO-RESPONSE REGULATORS PRR9/7/5 [11, 12], negative regulators of hypocotyl elongation [13, 14], were described to associate to G boxes [15], the DNA motifs recognized by the PIFs [16, 17], suggesting that PRR and PIF function might converge antagonistically to regulate growth. Here we report that PRR9/7/5 and PIFs physically interact and bind to the same promoter region of pre-dawn-phased, growth-related genes, and we identify the transcription factor CDF5 [18, 19] as target of this interplay. In SD, CDF5 expression is sequentially repressed from morning to dusk by PRRs and induced pre-dawn by PIFs. Consequently, CDF5 accumulates specifically at dawn, when it induces cell elongation. Our findings provide a framework for recent TIMING OF CAB EXPRESSION 1 (TOC1/PRR1) data [5, 20] and reveal that the long described circadian morning-to-midnight waves of the PRR transcriptional repressors (PRR9, PRR7, PRR5, and TOC1) [21] jointly gate PIF activity to dawn to prevent overgrowth through sequential regulation of common PIF-PRR target genes such as CDF5

Seedling establishment : a a dimmer switch-regulated process between dark and light signaling

By being exquisitely sensitive to their light surroundings, plants are able to continuously adjust their growth to optimize fitness. Darkness is an important cue for plants and a time when they actively grow and develop through regulation of the appropriate gene networks and biochemical changes. Although plants might not possess "dark receptors," inactive photoreceptors facilitate activation and inhibition of dark-specific processes, and thus darkness itself might be considered a signal triggering a myriad of responses. In this Update, we review the effects of dark and light signaling during seedling establishment. We describe the features of seedlings germinated in the dark and their switch in development upon emerging into the light. We examine how aboveground growth is regulated by the duration of dark/light cycles and how circadian clock signaling is integrated. 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 (Franklin et al., 2014; 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

Seedling establishment under stress: A signalling role for chloroplasts

Trabajo presentado en International Conference on Arabidopsis Research (ICAR2022), evento celebrado en Belfast (Irlanda del Norte) entre el 20 y el 24 de junio de 2022.Peer reviewe

Metal halide perovskite toxicity effects on Arabidopsis thaliana plants are caused by iodide ions

Highly efficient solar cells containing lead halide perovskites are expected to revolutionize sustainable energy production in the coming years. Perovskites are generally assumed to be toxic because of the lead (Pb), but experimental evidence to support this prediction is scarce. We tested the toxicity of the perovskite MAPbI3 (MA = CH3NH3) and several precursors in Arabidopsis thaliana plants. Both MAPbI3 and the precursor MAI hamper plant growth at concentrations above 5 μM. Lead-based precursors without iodide are only toxic above 500 μM. Iodine accumulation in Arabidopsis correlates with growth inhibition at much lower concentrations than lead. This reveals that perovskite toxicity at low concentrations is caused by iodide ions specifically, instead of lead. We calculate that toxicity thresholds for iodide, but not lead, are likely to be reached in soils upon perovskite leakage. This work stresses the importance to further understand and predict harmful effects of iodide-containing perovskites in the environment