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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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.
The authors declare no competing financial interests.
About this article
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