Ohman D, Demedts B, Kumar M, Gerber L, Gorzsás A, Goeminne G, Hedenström M, Ellis B, Boerjan W, Sundberg B
MYB103 is required for FERULATE-5-HYDROXYLASE expression and syringyl lignin biosynthesis in Arabidopsis stems
Plant J. 2012 Sep 12. [Epub ahead of print]

Abstract
The transcription factor (TF) MYB103 has earlier been identified as a member in the transcriptional network regulating secondary wall biosynthesis in xylem tissues of Arabidopsis and proposed to act on cellulose biosynthesis. It is a direct transcriptional target of the TF SECONDARY WALL ASSOCIATED NAC DOMAIN PROTEIN 1 (SND1), and 35S-driven dominant repression or over-expression of MYB103 modifies secondary wall thickness. We identified two myb103 T-DNA insertion mutants and chemically characterised their lignocellulose by pyrolysis-GC/MS, 2D NMR, FT-IR microspectroscopy and wet chemistry. The mutants developed normally but exhibited a large change in their cell wall chemistry, marked by a 70-75% decrease in syringyl (S) lignin. Guaiacyl (G) lignin was co-ordinately increased, so that total Klason lignin was not affected. Transcript abundance of FERULATE-5-HYDROXYLASE (F5H), the key gene in S-lignin biosynthesis, was strongly decreased in the myb103 mutants, and the metabolome of the myb103 mutant and of a null mutant in F5H was very similar. Other than the modification in lignin S to G ratio, there were only very minor changes in the composition of secondary cell wall polymers in the inflorescence stem. In conclusion, we demonstrate that F5H expression and, hence, S-lignin biosynthesis is dependent on MYB103.

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