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

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.

油菜素内酯（Brassinosteroid，BR）与赤霉素（gibberellin，GA）可在植物中调控诸多相似的发育响应，但二者的调控关联仍未明晰。本研究发现，BR激活的BZR1与GA失活的DELLA转录调控因子之间存在直接相互作用，二者发挥功能时存在相互依赖的关系。GA促进细胞伸长的过程依赖BR信号通路，而BR或激活型BZR1可抑制GA缺陷型矮化表型。DELLA蛋白可直接与BZR1结合，且在体外与体内均能抑制BZR1与DNA的结合能力。全基因组分析鉴定出一类受GA调控且依赖BZR1的转录组，该转录组富集光调控基因以及参与细胞壁合成、光合作用/叶绿体功能的基因。GA促进下胚轴伸长的过程同时需要BZR1与光敏色素互作因子（phytochrome interacting factors，PIFs），以及二者共有的下游靶基因PREs。本研究结果表明，GA可解除DELLA介导的BZR1抑制作用，且DELLA-BZR1-PIF4互作构成了核心转录模块，介导GA、BR与光信号协同调控植物生长。总体实验设计：将野生型拟南芥与bzr1-1D突变体接种于含有1 μM PAC、0或2 μM PPZ的培养基中，黑暗培养4.5天，随后用10 μM GA3或空白对照溶液处理12小时。采用Spectrum植物总RNA提取试剂盒（Sigma）提取总RNA，使用TruSeq™ RNA样本制备试剂盒（Illumina）构建带条形码的mRNA测序文库。将6个带条形码的文库混合后，通过Illumina HiSeq2000进行测序。