Populus GT43 family members group into distinct sets required for primary and secondary wall xylan biosynthesis and include useful promoters for wood modification.

The plant GT43 protein family includes xylosyltransferases that are known to be required for xylan backbone biosynthesis, but have incompletely understood specificities. RT-q PCR and histochemical ( GUS) analyses of expression patterns of GT43 members in hybrid aspen, reported here, revealed that three clades of the family have markedly differing specificity towards secondary wall-forming cells (wood and extraxylary fibres). Intriguingly, GT43 A and B genes (corresponding to the Arabidopsis IRX9 clade) showed higher specificity for secondary-walled cells than GT43 C and D genes ( IRX14 clade), although both IRX9 and IRX14 are required for xylosyltransferase activity. The remaining genes, GT43 E, F and G ( IRX9- L clade), showed broad expression patterns. Transient transactivation analyses of GT43 A and B reporters demonstrated that they are activated by Ptxt MYB021 and PNAC085 (master secondary wall switches), mediated in Ptxt MYB021 activation by an AC element. The high observed secondary cell wall specificity of GT43 B expression prompted tests of the efficiency of its promoter ( p GT43 B), relative to the Ca MV 35 S ( 35 S) promoter, for overexpressing a xylan acetyl esterase ( CE5) or downregulating REDUCED WALL ACETYLATION ( RWA) family genes and thus engineering wood acetylation. CE5 expression was weaker when driven by p GT43 B, but it reduced wood acetyl content substantially more efficiently than the 35 S promoter. RNAi silencing of the RWA family, which was ineffective using 35 S, was achieved when using GT43 B promoter. These results show the utility of the GT43 B promoter for genetically engineering properties of wood and fibres. [ABSTRACT FROM AUTHOR]