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Plant and Cell Physiology Advance Access originally published online on November 27, 2006
Plant and Cell Physiology 2007 48(1):74-83; doi:10.1093/pcp/pcl039
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© The Author 2006. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Co-Regulation of Brassinosteroid Biosynthesis-Related Genes During Xylem Cell Differentiation

Ryo Yamamoto1,4,*, Shozo Fujioka2, Kuninori Iwamoto1, Taku Demura1,5, Suguru Takatsuto3, Shigeo Yoshida2 and Hiroo Fukuda1,*

1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033 Japan
2Discovery Research Institute, RIKEN, Wako, 351-0198 Japan
3Department of Chemistry, Joetsu University of Education, Joetsu, 943-8512 Japan

*Corresponding authors: Ryo Yamamoto, E-mail, brassin{at}affrc.go.jp; Fax, +81-29-838-8392; Hiroo Fukuda, E-mail, fukuda{at}biol.s.u-tokyo.ac.jp; Fax, +81-3-3812-4929.


  Abstract

To understand the regulatory mechanisms of brassinosteroid (BR) biosynthesis in specific plant developmental processes, we first investigated the accumulation profiles of BRs and sterols in xylem differentiation in a Zinnia culture. The amounts of many substances in the late C28 sterol biosynthetic pathway to campesterol (CR), such as episterol and 24-methylenecholesterol, as well as those in the BR-specific biosynthetic pathway from CR to brassinolide (BL), were elevated in close association with tracheary element differentiation. Among them, 6-deoxotyphasterol (6-deoxoTY) accumulated to unusually high levels within cells cultured in tracheary element-inductive medium, while castasterone (CS) was not elevated either within or outside cells. To identify the molecular basis of this co-up-regulation of BRs and C28 sterols, we isolated Zinnia genes for the key enzymes of BR biosynthesis, ZeSTE1, ZeDIM, ZeDWF4, ZeCPD1 and ZeCPD2. RNA gel blot analysis of these genes indicated a coordinated increase in transcripts for ZeSTE1, ZeDIM, ZeDWF4 and ZeCPD1, and a tracheary element differentiation-specific increase in transcripts for ZeDWF4 and ZeCPD1. In situ hybridization experiments of ZeDWF4 and ZeCPD1 mRNAs revealed their preferential accumulation in procambium cells, immature xylem cells and xylem parenchyma cells. These results suggest that BR biosynthesis during tracheary element differentiation may be regulated by the coordinated regulation of broad sterol biosynthesis and specific regulation of BR biosynthesis, which occurs in part by elevated transcript levels of genes encoding BR biosynthetic enzymes, specifically ZeDWF4 and ZeCPD1. These data provide new insights into the regulation of BR biosynthesis and BR signaling during plant development.

Keywords: Auxin - Brassinosteroid biosynthesis - Cytokinin - Gene expression - Tracheary element differentiation - Zinnia elegans

Abbreviations: BA, 6-benzylaminopurine; BL, brassinolide; BR, brassinosteroid; CN, campestanol; CR, campesterol; CS, castasterone; CT, cathasterone; 6-deoxoCS, 6-deoxocastasterone; 6-deoxoCT, 6-deoxocathasterone; 6-deoxoTE, 6-deoxoteasterone; 6-deoxoTY, 6-deoxotyphasterol; 6-oxoCN, 6-oxocampestanol; DIG, digoxigenin; GC-MS, gas chromatography–mass spectrometry; GC-SIM, gas chromatography–selective ion monitoring; NAA, 1-naphthalene acetic acid; RT–PCR, reverse transcription–PCR; TE, teasterone; TY, typhasterol

4 Present address: National Institute of Crop Science (NICS), Tsukuba, 305-8518 Japan.

5 Present address: Plant Science Center, RIKEN, Yokohama, 230-0045 Japan.

The nucleotide sequences reported in this paper have been submitted to the DDBJ database under accession numbers ZeCPD1 (AB231153), ZeCPD2 (AB231154), ZeDWF4 (AB231155), ZeDIM (AB231156) and ZeSTE1 (AB231157).

(Received August 28, 2006; Accepted November 16, 2006)
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