Brassinosteroid, gibberellin and phytochrome impinge on a common transcription module in Arabidopsis

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Brassinosteroid and gibberellin promote many similar developmental responses in plants; however, their relationship remains unclear. Here we show that BR and GA act interdependently through a direct interaction between the BR-activated BZR1 and GA-inactivated DELLA transcription regulators. GA promotion of cell elongation required BR signalling, whereas BR or active BZR1 suppressed the GA-deficient dwarf phenotype. DELLAs directly interacted with BZR1 and inhibited BZR1–DNA binding both in vitro and in vivo. Genome-wide analysis defined a BZR1-dependent GA-regulated transcriptome, which is enriched with light-regulated genes and genes involved in cell wall synthesis and photosynthesis/chloroplast function. GA promotion of hypocotyl elongation requires both BZR1 and the phytochrome-interacting factors (PIFs), as well as their common downstream targets encoding the PRE-family helix–loop–helix factors. The results demonstrate that GA releases DELLA-mediated inhibition of BZR1, and that the DELLA–BZR1–PIF4 interaction defines a core transcription module that mediates coordinated growth regulation by GA, BR and light signals.

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Figure 1: BR signalling and BZR1 activity are required for GA promotion of hypocotyl elongation.
Figure 2: RGA interacts with BZR1 and inhibits the DNA-binding activity of BZR1 in vitro and in vivo.
Figure 3: GA and BR co-regulate a large number of genes through DELLAs and BZR1.
Figure 4: BZR1 and PIF4 are required for the GA promotion of hypocotyl elongation.
Figure 5: GA promotion of cell elongation requires the BZR1 and PIF4 targets, PREs.

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We thank X. W. Deng (Department of Molecular, Cellular, and Developmental Biology, Yale University) for providing seeds of the della pentuple mutant. This study was supported by grants from the NIH (R01GM066258 to Z.Y.W.) and from the NSF (MCB-0923723 to T.P.S.). J-X.S. was supported by the China Scholarship Council.

Author information

M-Y.B. and Z-Y.W. together designed the experiments. M-Y.B. performed statistical analysis of plant growth, ChIP–qPCR, DNA-binding assay, RNA-Seq, RT–qPCR and together with E.O. and Y.B. analysed microarray and RNA-Seq data.J-X.S. performed the yeast two-hybrid, co-immunoprecipitation, protein–protein pulldown, transient expression assays and generated bzr1-1D/ga1-3. E.O. analysed bzr1-1D/PIF4-Ox and bzr1-1D/pifq. M.F. analysed the GA responses of IBH1-Ox. R.Z. performed RGA protein degradation studies. T-p.S. provided sly1-10 seeds and helped with critical discussion on the work. M-Y.B. performed all other experiments. M-Y.B. and Z-Y.W. wrote the manuscript.

Correspondence to Zhi-Yong Wang.

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