Journal Article

SABATH methyltransferases from white spruce (<i>Picea glauca</i>): gene cloning, functional characterization and structural analysis

Nan Zhao, Brian Boyle, Isabelle Duval, Jean-Luc Ferrer, Hong Lin, Armand Seguin, John Mackay and Feng Chen

in Tree Physiology

Volume 29, issue 7, pages 947-957
Published in print July 2009 | ISSN: 0829-318X
Published online July 2009 | e-ISSN: 1758-4469 | DOI:
SABATH methyltransferases from white spruce (Picea glauca): gene cloning, functional characterization and structural analysis

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Known members of the plant SABATH family of methyltransferases have important biological functions by methylating hormones, signalling molecules and other metabolites. While all previously characterized SABATH genes were isolated from angiosperms, in this article, we report on the isolation and functional characterization of SABATH genes from white spruce (Picea glauca [Moench] Voss), a gymnosperm. Through EST database search, three genes that encode proteins significantly homologous to known SABATH proteins were identified from white spruce. They were named PgSABATH1, PgSABATH2 and PgSABATH3, respectively. Full length cDNAs of these three genes were cloned and expressed in Escherichia coli. The E. coli-expressed recombinant proteins were tested for methyltransferase activity with a large number of compounds. While no activity was detected for PgSABATH2 and PgSABATH3, PgSABATH1 displayed the highest level of catalytic activity with indole-3-acetic acid (IAA). PgSABATH1 was, therefore, renamed PgIAMT1. Under steady-state conditions, PgIAMT1 exhibited apparent K m values of 18.2 μM for IAA. Homology-based structural modelling of PgIAMT1 revealed that the active site of PgIAMT1 is highly similar to other characterized IAMTs from angiosperms. PgIAMT1 showed expression in multiple tissues, with the highest level of expression detected in embryonic tissues. During somatic embryo maturation, a significant reduction in PgIAMT1 transcript levels was observed when developing cotyledons become apparent which is indicative of mature embryos. The biological roles of white spruce SABATH genes, especially those of PgIAMT1, and the evolution of the SABATH family are discussed.

Keywords: gene expression; high-throughput enzyme assay; indole-3-acetic acid; somatic embryogenesis

Journal Article.  6344 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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