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

Abstract

SummaryThe plant GT43 protein family includes xylosyltransferases that are known to be required for xylan backbone biosynthesis, but have incompletely understood specificities. RT-qPCR 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, GT43A and B genes (corresponding to the Arabidopsis IRX9 clade) showed higher specificity for secondary-walled cells than GT43C and D genes (IRX14 clade), although both IRX9 and IRX14 are required for xylosyltransferase activity. The remaining genes, GT43E, F and G (IRX9-L clade), showed broad expression patterns. Transient transactivation analyses of GT43A and B reporters demonstrated that they are activated by PtxtMYB021 and PNAC085 (master secondary wall switches), mediated in PtxtMYB021 activation by an AC element. The high observed secondary cell wall specificity of GT43B expression prompted tests of the efficiency of its promoter (pGT43B), relative to the CaMV 35S (35S) 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 pGT43B, but it reduced wood acetyl content substantially more efficiently than the 35S promoter. RNAi silencing of the RWA family, which was ineffective using 35S, was achieved when using GT43B promoter. These results show the utility of the GT43B promoter for genetically engineering properties of wood and fibres.

Different Routes for Conifer- and Sinapaldehyde and Higher Saccharification upon Deficiency in the Dehydrogenase CAD1

“…S2B). This effective down-regulation is in contrast with previous studies claiming that the 35S promoter is not the most effective promoter for RNAi silencing of secondary CW-related genes compared with xylem-specific promoters such as the GT43B promoter (Ratke et al, 2015). However, this apparent contradiction might be explained by the specific nature of lignification, which is under both cell-autonomous and non-cellautonomous control (Pesquet et al, 2013;Smith et al, 2013Smith et al, , 2017.…”

“…It has been hypothesized that monolignols synthesized in the ray cells diffuse toward the neighboring xylem cells (Hawkins et al, 1997). Because the 35S promoter confers strong expression in rays in secondary xylem (Nilsson et al, 1996;Chen et al, 2000;Ratke et al, 2015), it is expected that the expression of PtaCAD1 is silenced in these cells, reducing a major source of monolignols destined for lignification of the neighboring xylem cells.…”

AspWood: High-Spatial-Resolution Transcriptome Profiles Reveal Uncharacterized Modularity of Wood Formation in Populus tremula

“…PtGT43E showed a very different expression profile, with a broad expression peak in primary walled cells. These observations support the recently suggested concept that separate primary and secondary xylan synthase complexes exist, similar to primary and secondary cellulose synthase complexes (Mortimer et al, 2015;Ratke et al, 2015), with PtGT43E (IRX9L) and PtGT43C/D (IRX14) forming the primary (A) Expression profiles for pectin and xyloglucan biosynthetic genes. All genes are highly expressed during primary wall biosynthesis, but also at later stages during xylem development.…”

“…At least three interacting glycosyltransferases (GTs) of this complex have been identified, i.e., one GT47 member (IRX10/10L) and two GT43 members (IRX9/9L and IRX14/14L) (Jensen et al, 2014;Urbanowicz et al, 2014;Mortimer et al, 2015;Zeng et al, 2016). In Populus, IRX9/9L function is performed by PtGT43A, B, or E and IRX14/14L function by PtGT43C or D (Lee et al, 2011;Ratke et al, 2015). In AspWood, expression of PtGT43A and B was almost identical and closely resembled that of SCW CesAs, whereas expression of the genes encoding their interacting partners PtGT43C or D was slightly different, with higher expression in primary-walled tissues ( Figure 5C).…”

Asparagus IRX9, IRX10, and IRX14A Are Components of an Active Xylan Backbone Synthase Complex that Forms in the Golgi Apparatus

“…Mortimer et al (2015) proposed that the Arabidopsis primary wall xylan biosynthetic machinery likely consists of AtGUX3, AtIRX9L, AtIRX10L, and AtIRX14. It is possible that two distinct sets of XSCs are responsible for primary and secondary wall xylan biosynthesis, as proposed previously by Ratke et al (2015). This would be similar to the cellulose synthases (CESAs) for primary wall (CESA1, CESA3, and CESA6) and secondary wall (CESA4, CESA7, and CESA8) in Arabidopsis (Carroll et al, 2012).…”