Gibberellins (GAs) and brassinosteroids (BRs) are important phytohormones that control plant development and responses to environmental cues by involving DELLA proteins and BRASSINAZOLE-RESISTANT1 (BZR1) respectively as key transcription factors. Here, we reveal a new role for JUNGBRUNNEN1 (JUB1) as a transcriptional regulator of GA/BR signalling in Arabidopsis thaliana. JUB1 directly represses the hormone biosynthesis genes GA3ox1 and DWARF4 (DWF4), leading to reduced levels of GAs and BRs and typical GA/BR deficiency phenotypes exhibiting short hypocotyls, dwarfism, late flowering and male sterility. JUB1 also directly represses PHYTOCHROME INTERACTING FACTOR4 (PIF4), a transcription factor connecting hormonal and environmental stimuli. On the other hand, JUB1 activates the DELLA genes GA INSENSITIVE (GAI) and RGA-LIKE 1 (RGL1). In addition, BZR1 and PIF4 act as direct transcriptional repressors upstream of JUB1, establishing a negative feedback loop. Thus, JUB1 forms the core of a robust regulatory module that triggers DELLA accumulation, thereby restricting cell elongation while concomitantly enhancing stress tolerance.

Department of Plant Science Plant Genomics and Breeding Institute Research Institute of Agriculture and Life Sciences Seoul National University Seoul 151 921 Korea

Laboratory of Growth Regulators Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany ASCR and Palacky University v v i Slechtitelu 11 CZ 783 71 Olomouc Czech Republic

Max Planck Institute of Molecular Plant Physiology Am Mühlenberg 1 14476 Potsdam Golm Germany

University of Potsdam Institute of Biochemistry and Biology Karl Liebknecht Straße 24 25 Haus 20 14476 Potsdam Golm Germany

Nat Plants. 2016 Mar 02;2:16023. doi: 10.1038/nplants.2016.23. PubMed

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