Plant Molecular Biology

, Volume 80, Issue 4–5, pp 489–501 | Cite as

Constitutive activation of brassinosteroid signaling in the Arabidopsis elongated-D/bak1 mutant

  • Yuhee Chung
  • Vitnary Choe
  • Shozo Fujioka
  • Suguru Takatsuto
  • Muho Han
  • Jong-Seong Jeon
  • Youn-Il Park
  • Kyun Oh Lee
  • Sunghwa Choe


Defects in brassinosteroid (BR) biosynthetic or signaling genes result in dwarfed plants, whereas overexpression of these genes increases overall stature. An Arabidopsis elongated-D (elg-D) mutant shares phenotypic similarities with BR overexpression lines, suggesting its implication in BR pathways. Here, we determine how elg-D affects BR signaling. Since elg-D rescued dwarfism in bri1-5 plants, a BR receptor mutant, but not in BR-insensitive bin2/dwf12-1D plants, elg-D appears to act between bri1-5 and bin2/dwf12-1D in BR signaling. We found that elg-D had an increased response to epi-brassinolide (epi-BL); that the BES1 transcription factor was shifted toward the dephosphorylated form in elg-D; that the expression of a BR responsive gene, SAUR-AC1, was upregulated in elg-D; and that transcription of BR biosynthetic genes, DWF4 and CPD, was downregulated by feedback inhibition. Thus, endogenous levels of CS and BL as well as biosynthetic intermediates were reduced by the elg-D mutation, whereas basal levels of BR signaling were elevated. Map-based cloning and sequencing revealed that elg-D is allelic to the BR co-receptor protein, BAK1, and has an Asp122 to Asn substitution in the third repeat of the extracellular leucine-rich repeat (LRR) domain. In agreement with the finding that BAK1/ELG is involved in the perception of pathogen-associated molecular patterns (PAMPs), the bak1/elg-D plants exhibited increased Pseudomonas syringae growth. Therefore, bak1/elg-D promotes Arabidopsis growth by stimulating BR signaling at the expense of its readiness to respond to biotic stress factors. The BAK1/ELG BR co-receptor thus plays an important role in BR signaling that is mediated by its LRR domain.


Brassinosteroids BAK1 BRI1 Cell elongation Leucine-rich repeat receptor-like kinase 









Leucine-rich repeat






Endoplasmic reticulum quality control


Pathogen-associated molecular patterns



We would like to thank Mi Kwon for technical assistance and Yanhai Yin for providing the anti-BES1 antibody. This research was supported, in part, by grants from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No. PJ008051), Rural Development Administration, Republic of Korea; the Technology Development Program (110033-5) for Agriculture and Forestry, Ministry for Food, Agriculture, Forestry and Fisheries, Republic of Korea and the Basic Science Research Program through the National Research Foundation of Korea (NRF), which is funded by the Ministry of Education, Science and Technology (2010-0012736) (to SC); the BK21 Research Fellowships, funded by the Ministry of Education, Science, and Technology of the Korean Government (to YC); and a Grant-in-Aid for Scientific Research (B) from the Ministry of Education, Culture, Sports, Science and Technology of Japan (no. 19380069 and 23380066 to SF).


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Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  • Yuhee Chung
    • 1
  • Vitnary Choe
    • 1
  • Shozo Fujioka
    • 2
  • Suguru Takatsuto
    • 3
  • Muho Han
    • 4
  • Jong-Seong Jeon
    • 4
  • Youn-Il Park
    • 5
  • Kyun Oh Lee
    • 6
  • Sunghwa Choe
    • 1
    • 7
  1. 1.School of Biological Sciences, College of Natural SciencesSeoul National UniversitySeoulKorea
  2. 2.RIKEN Advanced Science InstituteSaitamaJapan
  3. 3.Department of ChemistryJoetsu University of EducationNiigataJapan
  4. 4.Graduate School of BiotechnologyKyung Hee UniversityYonginKorea
  5. 5.Department of BiologyChungnam National UniversityDaejeonKorea
  6. 6.Division of Applied Life ScienceGyeongsang National UniversityJinjuKorea
  7. 7.Plant Genomics and Breeding InstituteSeoul National UniversitySeoulKorea

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