Brassinosteroid biosynthesis is modulated via a transcription factor cascade of COG1, PIF4 and PIF5

Wei Y., Zuan T., Tarkowská D., Kim J., Nam H.G., Novák O., He K., Gou X., Li J.

Keywords: Brassinosteroid, COG1, PIF4, PIF5, BR homeostasis, hypocotyl elongation, DWF4, BR6ox2
Abstract: Brassinosteroids (BRs) are essential phytohormones regulating various developmental and physiological processes during normal growth and development. cog1-3D (cogwheel 1-3D) was identified as an activation-tagged genetic modifier of bri1-5, an intermediate BR receptor mutant. COG1 encodes a Dof-type transcription factor previously found to act as a negative regulator of the phytochrome signaling pathway. cog1-3D single mutants show an elongated hypocotyl phenotype under light conditions. Loss-of-function by ethylmethanoesulfonate (EMS) mutation or inducible expression of a dominant-negative form of COG1 results in an opposite phenotype. BR profile assay indicated that BR levels are elevated in cog1-3D seedlings. Quantitative RT-PCR analyses showed that several key BR biosynthetic genes are significantly up-regulated in cog1-3D compared to those of wild-type. Two basic helix-loop-helix transcription factors, PIF4 and PIF5, were found to be transcriptionally up-regulated in cog1-3D. Genetic analysis indicated that PIF4 and PIF5 were required for COG1 to promote BR biosynthesis and hypocotyl elongation. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays (EMSA) demonstrated that COG1 binds to the promoter regions of PIF4 and PIF5; and PIF4 and PIF5 binds to the promoter regions of key BR biosynthetic genes, such as DWF4 and BR6ox2, to directly promote their expression. These results demonstrate that COG1 regulates BR biosynthesis via up-regulating the transcription of PIF4 and PIF5.
DOI: 10.​1104/​pp.​16.​01778
IEB authors: Ondřej Novák, Danuše Tarkowská