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Spatiotemporal analysis of shade-induced transcriptional reprogramming in Arabidopsis reveals patterns underlying organ-specific growth

ABSTRACT: In response to neighbor proximity plants increase growth of specific organs (e.g. hypocotyl) to enhance access to sunlight. Shade enhances the activity of Phytochrome Interacting Factors (PIFs) by releasing those bHLH transcription factors from phytochrome B-mediated inhibition. PIFs promote elongation by inducing auxin production in cotyledons. In order to elucidate spatiotemporal aspects of the neighbor proximity response, we analyzed changes in transcript abundance at different time points during a shade treatment in dissected cotyledons and hypocotyls. We concentrated our analysis on these two organs because the former is considered as the primary shade-sensing organ while elongation is rapidly triggered in the hypocotyl. We conclude that PIFs initiate transcriptional reprogramming in both organs within 15 minutes comprising regulated expression of several early auxin response genes. This suggests that hypocotyl growth is elicited by both local and distal auxin signals. With time the transcriptional response diverges increasingly between organs. We identify genes whose differential expression may underlie organ-specific elongation. Finally, we uncover a growth promotion gene expression signature shared between responses to different environments and organs.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE81202 | GEO | 2017/01/17

SECONDARY ACCESSION(S): PRJNA320878

REPOSITORIES: GEO

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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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Spatiotemporal analysis of shade-induced transcriptional reprogramming in Arabidopsis reveals patterns underlying organ-specific growth

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