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

Brassinosteroid (BR) and gibberellin (GA) promote many similar developmental responses in plants; but their relationship remains unclear. Here we show that BR and GA act interdependently through a direct interaction between the BR-activated BZR1 and GAinactivated DELLA transcription regulators. GA promotion of cell elongation required BR signaling, whereas BR or active BZR1 can suppresssed 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. GA promotion of hypocotyl elongation requires both BZR1 and the phytochrome interacting factors (PIFs), as well as their common downstream targets PREs. 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. Overall design: Wild type Arabidopsis and bzr1-1D were grown in media containing 1 μM PAC and 0 or 2 μM PPZ for 4.5 days in dark, then treated with 10 μM GA3 or mock solution for 12 hr. Total RNA was extracted with Spectrum Plant Total RNA Kit (Sigma) and the mRNA sequencing libraries were constructed with barcodes using TruSeqTM RNA Sample Preparation Kit (Illumina). Six barcoded libraries were pooled together and sequenced by Illumina HiSeq2000.