Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Hypocotyl and cotyledon transcriptome in Arabidopsis thaliana treated with 1 ppm ethylene and shade (low PAR, low blue and low R:FR)

ABSTRACT: Plants have evolved shoot elongation mechanisms to escape from diverse environmental stresses such as flooding and vegetative shade. The apparent similarity in growth responses suggests possible convergence of the signalling pathways. Shoot elongation is mediated by passive ethylene accumulating in flooded plant organs and by changes in light quality and quantity under vegetation shade. Here we study hypocotyl elongation as a proxy for shoot elongation and delineated Arabidopsis hypocotyl length kinetics in response to ethylene and shade. Based on these kinetics, we further investigated ethylene and shade-induced genome-wide gene expression changes in hypocotyls and cotyledons separately. Both treatments induced a more extensive transcriptome reconfiguration in the hypocotyls compared to the cotyledons. Bioinformatics analyses suggested contrasting regulation of growth promotion- and photosynthesis-related genes. These analyses also suggested an induction of auxin, brassinosteroid and gibberellin signatures and the involvement of several candidate regulators in the elongating hypocotyls. Pharmacological and mutant analyses confirmed the functional involvement of several of these candidate genes and physiological control points in regulating stress-escape responses to different environmental stimuli. We discuss how these signaling networks might be integrated and conclude that plants, when facing different stresses, utilise a conserved set of transcriptionally regulated genes to modulate and fine tune growth. 1 day old Arabidopsis seedlings were subjected to control, ethylene and shade conditions. Hypocotyl and cotyledon tissues were harvested at 1.5 h, 13.5 h and 25.5 h of treatment time respectively. Microarray hybridization was carried out with 3 biological replicates (collected over 3 independent experiments) of each sample using the Affymetrix Arabidopsis Gene 1.1 ST platform.

ORGANISM(S): Arabidopsis thaliana

SUBMITTER: Rashmi Sasidharan

PROVIDER: E-GEOD-83212 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:In dense plant stands, the ratio between red and far-red (R:FR) light declines and shade intolerant species will respond to this cue for future shade by inducing the shade avoidance syndrome (SAS), enabling them to outgrow their neighbours. Shade tolerant species from the forest understory are unable to outgrow neighbouring trees and will suppress SAS. Although the molecular mechanisms underlying SAS are well studied in various species, mechanisms of SAS-suppression in shade tolerant species have rarely been studied. We applied RNA sequencing on Geranium pyrenaicum and G. robertianum, two wild species with contrasting growth responses to low R:FR light. G. pyrenaicum strongly induces petiole elongation when exposed to low R:FR light, at any time of the photoperiod. Contrastingly, G. robertianum only induces this response early in the day, and suppresses petiole growth in low R:FR light at the end of the photoperiod, which results after 24 hours in a net difference with control treatments of zero. We compared expression patterns in the most apical (most responsive) part of the second petioles, in two-week-old Geranium plants (two leaf stage) after 2 and 11.5 hours of far-red light enrichment. This way, we identified a number of novel candidate regulators of shade avoidance, and differential phytochrome control of plant immunity genes in the two species. For de-novo assembly of the reference transcriptomes, we pooled petiole- and leaf lamina tissue exposed to normal white light (180 mol m-2 s-1 PAR, R:FR 1.8, Â± 60 mol m-2 s-1 blue light), low R:FR light (0.2), blue-depleted light (Â± 4 mol m-2 s-1 blue) and green shade (50 mol m-2 s-1 PAR, R:FR 0.45, Â± 13 mol m-2 s-1 blue) for 2, 11.5 and 24 hours. Libraries of these samples were normalized, Illumina sequenced, and together with sequences of non-normalized petiole samples of the expression analysis constructed into a reference transcriptome for each species, using the Trinity protocol. Transcripts were clustered into orthologue clusters using the ortho-MCL clustering technique. Non-normalized libraries of samples (control vs. low R:FR light, 2 and 11.5 hours after start of the treatment) were sequenced and aligned to the newly assembled transcriptomes. Read counts were summed per orthologue cluster before statistical analysis was proceeded.

Project description:Plants grown under a canopy recognize changes in light quality and modify their growth patterns; this modification is known as shade avoidance syndrome. In leaves, leaf blade expansion is suppressed, whereas petiole elongation is promoted under the shade. However, the mechanisms that control these responses are largely unclear. Here, we demonstrated that both auxin and brassinosteroid (BR) are required for the normal leaf responses to shade. The microarray analysis of leaf blades and petioles treated with end-of-day far-red light (EODFR) revealed that almost half of the genes induced by the treatment in both parts were previously identified as auxin-responsive genes. Likewise, BR-responsive genes were overrepresented in the EODFR-induced genes. Hence, the auxin and BR responses were elevated by EODFR treatment in both leaf blades and petioles, although opposing growth responses were observed in these two parts. The analysis of the auxin-deficient doc1/big mutant and BR-deficient rot3/cyp90c1 mutant further indicates that auxin and BR were equally required for the normal petiole elongation response to the shade stimulus. In addition, the spotlight irradiation experiment revealed that phytochrome in leaf blades but not that in petioles regulated petiole elongation, which was probably mediated through regulation of the auxin/BR responses in petioles. On the basis of these findings, we conclude that auxin and BR cooperatively promote petiole elongation in response to the shade stimulus under the control of phytochrome in the leaf blade. The WT seedlings were grown for 19 days under continuous white light condition before experimental treatment with three light conditions. Seedlings were either maintained in white light for 2 h (WL), incubated in the dark condition for 2 h (D), or experienced a pulse irradiation of FR light before incubated in the dark condition for 2 h (FRD). Total RNAs were separately prepared from leaf blades and petioles after each light treatment. Three independent biological replicates were used.

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Hypocotyl and cotyledon transcriptome in Arabidopsis thaliana treated with 1 ppm ethylene and shade (low PAR, low blue and low R:FR)

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