Plant xylan (glucuronoxylan) biosynthesis module

A taxon-neutral decomposition of plant heteroxylan biosynthesis as a recursively decomposable module. Xylan is the dominant hemicellulose of the secondary cell wall: a (1->4)-beta-D-xylan backbone decorated with (alpha-1,2)-linked (4-O-methyl)glucuronic acid and O-acetyl groups in eudicots (glucuronoxylan, GX) and additionally with alpha-arabinofuranosyl and feruloyl-arabinose substitutions in grasses (glucuronoarabinoxylan, GAX). Xylan coats and tethers cellulose microfibrils and is covalently and non-covalently associated with lignin in the lignin-carbohydrate complex, so it is a major contributor to biomass recalcitrance and a key acetyl-group source that inhibits downstream fermentation. The module separates (1) Golgi backbone elongation by the IRX9/IRX10/IRX14 xylan synthase machinery, (2) synthesis of the reducing-end oligosaccharide sequence that may prime/terminate the chain in eudicots, (3) alpha-glucuronosyl sidechain addition (GUX), (4) 4-O-methylation of the glucuronic acid (GXM), and (5) O-acetylation (ESK1/TBL29 with RWA acetyl-CoA supply). It is phrased as functions, complexes, and pathway segments rather than a fixed gene list so it can represent eudicot GX and grass GAX implementations; concrete UniProt members are Arabidopsis exemplars, not species-restricting claims. As a bioenergy module, xylan substitution pattern (acetylation, methyl-GlcA) and quantity are principal engineering targets for reducing recalcitrance and acetate-driven fermentation inhibition.

MODULE:plant_xylan_biosynthesisDRAFTMetabolic Pathwaymodules/xylan_biosynthesis.yaml
xylan biosynthetic processGO:0045492 glucuronoxylan biosynthetic processGO:0010417
GO:0045492
xylan biosynthetic process
The module is grounded in the GO biological-process term for xylan biosynthesis; the eudicot-specific product is grounded to glucuronoxylan biosynthetic process (GO:0010417).
GO:0010417
glucuronoxylan biosynthetic process
The eudicot secondary-wall xylan is glucuronoxylan (GX); grass GAX adds arabinosyl/feruloyl substitutions on the same backbone.
UniProtKB:Q9FZJ1
beta-1,4-xylosyltransferase IRX10 (AtIRX10)
Arabidopsis exemplar GT47 catalytic xylosyltransferase elongating the (1->4)-beta-D-xylan backbone.
UniProtKB:Q940Q8
beta-1,4-xylosyltransferase IRX10L / XYLAN SYNTHASE-1 (AtIRX10L)
Purified IRX10L polymerises beta-1,4-xylan from UDP-xylose in vitro (PMID:25141999) and is the main backbone synthase of primary-wall xylan (PMID:26043357); redundant with IRX10 in secondary walls.
PMID:25141999
Two Arabidopsis proteins synthesize acetylated xylan in vitro.
Direct biochemical evidence that the GT47 IRX10-L is a xylan synthase.
PMID:26043357
An unusual xylan in Arabidopsis primary cell walls is synthesised by GUX3, IRX9L, IRX10L and IRX14.
Defines the primary-wall xylan synthase gene set and GUX3 as its sole glucuronyltransferase.
PMID:26951434
Asparagus IRX9, IRX10, and IRX14A Are Components of an Active Xylan Backbone Synthase Complex that Forms in the Golgi Apparatus.
Reconstitution in Nicotiana: all three of IRX9, IRX10 and IRX14A are needed for xylan xylosyltransferase activity in planta, and they interact.
PMID:29460505
Identification of an algal xylan synthase indicates that there is functional orthology between algal and plant cell wall biosynthesis.
KfXYS1 from the charophyte Klebsormidium is a beta-1,4-xylan synthase; IRX10/XYS1 orthologs occur among algae only in Klebsormidiophyceae and Zygnematophyceae.
PMID:39663842
XYLAN O-ACETYLTRANSFERASE 6 promotes xylan synthesis by forming a complex with IRX10 and governs wall formation in rice.
Rice IRX10 (BC18) polymerises xylan in vitro and forms a xylan synthase core with the O-acetyltransferase XOAT6.
UniProtKB:Q9ZQC6
beta-1,4-xylosyltransferase IRX9 (AtIRX9)
Arabidopsis exemplar GT43 component of the xylan synthase machinery (EC 2.4.2.24, 1,4-beta-D-xylan synthase); irx9 collapses xylem vessels.
UniProtKB:Q8L707
beta-1,4-xylosyltransferase IRX14 (AtIRX14)
Arabidopsis exemplar GT43 component partnering IRX9/IRX10 in backbone elongation.
UniProtKB:Q9ZUV3
Glucuronoxylan glucuronosyltransferase IRX7 / FRA8 (AtIRX7)
Arabidopsis exemplar GT47 enzyme required for the reducing-end oligosaccharide sequence of eudicot xylan.
UniProtKB:Q9FH36
Galacturonosyltransferase 12 / IRX8 (AtGAUT12)
Arabidopsis exemplar GT8 enzyme required for xylan reducing-end sequence and normal xylan amount; irx8 has severely reduced xylan.
UniProtKB:Q9LN68
Galacturonosyltransferase-like 1 / PARVUS (AtGATL1)
Arabidopsis exemplar GT8 enzyme contributing to the xylan reducing-end oligosaccharide sequence.
UniProtKB:Q9LSB1
UDP-glucuronate:xylan alpha-glucuronosyltransferase 1 / GUX1 (AtGUX1)
Arabidopsis exemplar GT8 enzyme adding (alpha-1,2)-glucuronic acid sidechains to the xylan backbone (GO:0080116).
UniProtKB:Q9LQ32
Glucuronoxylan 4-O-methyltransferase 3 / GXM3 (AtGXM3)
Arabidopsis exemplar 4-O-methylating the glucuronic acid sidechain to 4-O-methyl-GlcA (GO:0030775, EC 2.1.1.112).
UniProtKB:Q9LY46
Xylan O-acetyltransferase 1 / ESK1 / TBL29 (AtESK1)
Arabidopsis exemplar 2-O-/3-O-acetylating the xylan backbone (GO:1990538); esk1 has reduced xylan acetylation and collapsed xylem.
UniProtKB:Q0WW17
REDUCED WALL ACETYLATION 2 / RWA2 (AtRWA2)
Arabidopsis exemplar of the RWA family supplying acetyl donor to the Golgi lumen for wall polysaccharide O-acetylation.

Identifiers are grounded only where verified against the local GO term cache or UniProt; descriptors without a `term` (e.g. UDP-xylose donor, backbone oligosaccharide intermediates) are deliberate rather than oversights. The xylan backbone synthase is an IRX9/IRX10/IRX14 machine; IRX10 (GT47) is treated as the catalytic xylosyltransferase and IRX9/IRX14 (GT43) as required components. The backbone part carries a wall-type variant set: the secondary-wall set (IRX9/IRX10/IRX14) and the primary-wall set (IRX9L/IRX10L/IRX14, decorated by GUX3), per PMID:26043357. The GT47 xylan synthase predates land plants: the charophyte alga Klebsormidium has an active IRX10/XYS1 ortholog (PMID:29460505), while chlorophytes lack IRX10/XYS1 orthologs (some chlorophytes have minor 1,4-beta-xylans of unknown biosynthetic origin, PMID:30960338). The reducing-end oligosaccharide sequence (IRX7/FRA8, IRX8/GAUT12, PARVUS) is a eudicot feature and is marked optional; grasses lack this reducing-end tetramer. The grass glucuronoarabinoxylan variant (alpha-arabinofuranosyl and feruloyl-arabinose substitutions) is represented as a descriptor-level variant without an asserted UniProt exemplar because the arabinosyl/feruloyl transferase members are grass genes not verified here. Representative UniProt members are concrete Arabidopsis exemplars for orientation, not exhaustive or species-restricting.

10Nodes
7Parts
1Variant Sets
2Variants
10Annotons
5Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:plant_xylan_biosynthesis deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Reaction chaining (advisory)

✓ every PRECEDES step chains, or its break is acknowledged via chaining_status.

  • glucuronosyl_substitution → glcA_methylation [NOT_CHECKED]
    GUX first installs the GlcA sidechain; GXM then 4-O-methylates that same GlcA to 4-O-methyl-GlcA.

Function consistency and core coverage

6 gene-function check(s) reflected in core functions · 0 conflict(s) · 17 evidence or coverage gap(s) (26 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
xylan_synthase_activity PROTEIN_COMPLEX
Gene 		1,4-beta-D-xylan synthase activity
GO:0047517 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
irx10_catalytic IRX10 (Arabidopsis)
UniProtKB:Q9FZJ1
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx10_catalytic IRX10L / XYS1 (Arabidopsis)
UniProtKB:Q940Q8
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx10_catalytic IRX10 / BC18 (rice, LOC_Os01g70200)
UniProtKB:Q8S1X7
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx10_catalytic POPTR_001G068100 (poplar IRX10 ortholog)
UniProtKB:A0A2K2BTI7
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx10_catalytic GT47A / PpGT47A (Physcomitrium patens)
UniProtKB:A9RGD8
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx10_catalytic KfXYS1 (Klebsormidium nitens, KFL_003980130)
UniProtKB:A0A1Y1IIS5
Family Representative 		1,4-beta-D-xylan synthase activity
GO:0047517 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
irx9_irx14_components IRX9 (Arabidopsis)
UniProtKB:Q9ZQC6
Family Representative 		GT43 component of the xylan synthase complex
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
irx9_irx14_components IRX14 (Arabidopsis)
UniProtKB:Q8L707
Family Representative 		GT43 component of the xylan synthase complex
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
secondary_wall_xsc_activity PROTEIN_COMPLEX
Gene 		1,4-beta-D-xylan synthase activity
GO:0047517 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
primary_wall_xsc_activity PROTEIN_COMPLEX
Gene 		1,4-beta-D-xylan synthase activity
GO:0047517 		Participant Unchecked
No direct UniProt participant to compare. Abstract selectors and complex-wide activities cannot be inferred from donor or subunit gene reviews.
reducing_end_gts IRX7 / FRA8 (Arabidopsis)
UniProtKB:Q9ZUV3
Family Representative 		reducing-end oligosaccharide glycosyltransfer
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
reducing_end_gts GAUT12 / IRX8 (Arabidopsis)
UniProtKB:Q9FH36
Family Representative 		reducing-end oligosaccharide glycosyltransfer
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
reducing_end_gts PARVUS / GATL1 (Arabidopsis)
UniProtKB:Q9LN68
Family Representative 		reducing-end oligosaccharide glycosyltransfer
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
gux_activity GUX1 (Arabidopsis)
UniProtKB:Q9LSB1
Family Representative 		glucuronoxylan glucuronosyltransferase activity
GO:0080116 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.
gux_activity GUX3 (Arabidopsis; primary-wall xylan)
UniProtKB:Q8W4A7
Family Representative 		glucuronoxylan glucuronosyltransferase activity
GO:0080116 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.
gxm_activity GXM3 (Arabidopsis)
UniProtKB:Q9LQ32
Family Representative 		glucuronoxylan 4-O-methyltransferase activity
GO:0030775 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.
esk1_activity ESK1 / TBL29 (Arabidopsis; XOAT1)
UniProtKB:Q9LY46
Family Representative 		xylan O-acetyltransferase activity
GO:1990538 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.
rwa_activity RWA2 (Arabidopsis)
UniProtKB:Q0WW17
Family Representative 		Golgi acetyl donor provision for wall O-acetylation
No function ID 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked. The module function also lacks a GO identifier.
irx10_catalytic GT47 xylan synthase (IRX10/IRX10L)
Family 		1,4-beta-D-xylan synthase activity
GO:0047517 		Family Id Missing
The family has no identifier linking it to a curated family review.
irx9_irx14_components GT43 xylan synthase components (IRX9, IRX14)
Family 		GT43 component of the xylan synthase complex
No function ID 		No Function Id
The family function has no GO identifier for comparison; prose is not matched.
reducing_end_gts xylan reducing-end glycosyltransferases
Family 		reducing-end oligosaccharide glycosyltransfer
No function ID 		No Function Id
The family function has no GO identifier for comparison; prose is not matched.
gux_activity xylan alpha-(1,2)-glucuronosyltransferase (GUX)
Family 		glucuronoxylan glucuronosyltransferase activity
GO:0080116 		Family Id Missing
The family has no identifier linking it to a curated family review.
gxm_activity glucuronoxylan 4-O-methyltransferase (GXM/DUF579)
Family 		glucuronoxylan 4-O-methyltransferase activity
GO:0030775 		Family Id Missing
The family has no identifier linking it to a curated family review.
esk1_activity TBL/DUF231 xylan O-acetyltransferase (ESK1/TBL29)
Family 		xylan O-acetyltransferase activity
GO:1990538 		Family Id Missing
The family has no identifier linking it to a curated family review.
rwa_activity RWA acetyl-CoA supply protein
Family 		Golgi acetyl donor provision for wall O-acetylation
No function ID 		No Function Id
The family function has no GO identifier for comparison; prose is not matched.

Gene-review completeness (6/17 grounded genes reviewed)

6 complete review(s) · 0 with deep research · 11 missing review · 6 reviewed but lacking deep research

Gene Review Complete Deep research
GT47A A9RGD8 ✓ ✓ ✗
IRX10 Q8S1X7 ✓ ✓ ✗
IRX10 Q9FZJ1 ✓ ✓ ✗
IRX10L Q940Q8 ✓ ✓ ✗
KFL_003980130 A0A1Y1IIS5 ✓ ✓ ✗
POPTR_001G068100 A0A2K2BTI7 ✓ ✓ ✗
RWA2 (Arabidopsis) Q0WW17 ✗ — —
IRX14 (Arabidopsis) Q8L707 ✗ — —
GUX3 (Arabidopsis; primary-wall xylan) Q8W4A7 ✗ — —
GAUT12 / IRX8 (Arabidopsis) Q9FH36 ✗ — —
PARVUS / GATL1 (Arabidopsis) Q9LN68 ✗ — —
GXM3 (Arabidopsis) Q9LQ32 ✗ — —
GUX1 (Arabidopsis) Q9LSB1 ✗ — —
ESK1 / TBL29 (Arabidopsis; XOAT1) Q9LY46 ✗ — —
IRX9L / IRX9H (Arabidopsis, At1g27600) Q9SXC4 ✗ — —
IRX9 (Arabidopsis) Q9ZQC6 ✗ — —
IRX7 / FRA8 (Arabidopsis) Q9ZUV3 ✗ — —

Details

Context
eudicots (glucuronoxylan, GX)NCBITaxon:71240 grasses / commelinid monocots (glucuronoarabinoxylan, GAX)NCBITaxon:4734
Golgi membrane (site of xylan synthase machinery)GO:0000139 Golgi apparatus (lumenal substitution)GO:0005794
Plant xylan (glucuronoxylan) biosynthesisMetabolic Pathwayplant_xylan_biosynthesis
xylan biosynthetic processGO:0045492 glucuronoxylan biosynthetic processGO:0010417
Context
eudicots (glucuronoxylan, GX)NCBITaxon:71240 grasses / commelinid monocots (glucuronoarabinoxylan, GAX)NCBITaxon:4734
Golgi membrane (site of xylan synthase machinery)GO:0000139 Golgi apparatus (lumenal substitution)GO:0005794

Connections

The elongating xylan backbone is the acceptor for GlcA sidechain addition.
The reducing-end oligosaccharide sequence is proposed to prime/terminate eudicot backbone synthesis.
The backbone xylosyl residues are the acceptors for O-acetylation.
rwa_acetyl_supply -> esk1_acetyltransfer Provides Input For
RWA-supplied lumenal acetyl donor feeds the xylan O-acetyltransferase.
Part 1: (1->4)-beta-D-xylan backbone elongation
Xylan synthase machinery (IRX9/IRX10/IRX14)Protein Complexxylan_backbone_synthase

Golgi-membrane glycosyltransferase machinery that elongates the (1->4)-beta-D-xylan backbone from UDP-D-xylose. IRX10 (GT47) is the catalytic xylosyltransferase; IRX9 and IRX14 (GT43) are required, likely structural/co-catalytic, partners.

Annotons

1,4-beta-D-xylan synthase (backbone elongation)
xylan_synthase_activity
Participant: Protein Complex: xylan synthase complex (IRX9/IRX10/IRX14)
Protein Complex:
xylan synthase complex (IRX9/IRX10/IRX14) Golgi glycosyltransferase complex adding beta-1,4-xylosyl units to the growing backbone; catalytic GT47 (IRX10) plus GT43 components (IRX9, IRX14).

Function

1,4-beta-D-xylan synthase activityGO:0047517
Substrates: UDP-D-xylose (1->4)-beta-D-xylan (n)
Products: (1->4)-beta-D-xylan (n+1) UDP

Locations

Golgi membraneGO:0000139

Processive backbone elongation; the rate-defining core of xylan synthesis and the irregular-xylem (irx9/irx10/irx14) locus.

IRX10 catalytic xylosyltransferase
irx10_catalytic
Participant: Family: GT47 xylan synthase (IRX10/IRX10L)
Family:
GT47 xylan synthase (IRX10/IRX10L) PANTHER splits the Arabidopsis pair across two subfamilies of PTHR11062 (IRX10 in SF370, IRX10L in SF200), so no single family id is asserted here. Comparator members: rice IRX10 (grass glucuronoarabinoxylan), poplar (wood), moss (PpGT47A, active in vitro but with no knockout wall phenotype) and the charophyte alga Klebsormidium (KfXYS1), whose activity shows the clade predates land plants; chlorophytes such as Chlamydomonas have no member (genes/ARATH/IRX10/IRX10-bioinformatics/RESULTS.md).
Representative Members: IRX10 (Arabidopsis)UniProtKB:Q9FZJ1 IRX10L / XYS1 (Arabidopsis)UniProtKB:Q940Q8 IRX10 / BC18 (rice, LOC_Os01g70200)UniProtKB:Q8S1X7 POPTR_001G068100 (poplar IRX10 ortholog)UniProtKB:A0A2K2BTI7 GT47A / PpGT47A (Physcomitrium patens)UniProtKB:A9RGD8 KfXYS1 (Klebsormidium nitens, KFL_003980130)UniProtKB:A0A1Y1IIS5

Function

1,4-beta-D-xylan synthase activityGO:0047517
Substrates: UDP-D-xylose (1->4)-beta-D-xylan (n)
Products: (1->4)-beta-D-xylan (n+1) UDP

Processes

glucuronoxylan biosynthetic processGO:0010417

GT47 catalytic subunit transferring xylose from UDP-xylose to the non-reducing end of the backbone. Purified IRX10L polymerises beta-1,4-xylan alone in vitro (PMID:25141999); AtIRX10 and the moss and psyllium orthologs are xylan xylosyltransferases (PMID:25139408). IRX10 is the main secondary-wall gene and IRX10L the primary-wall gene; they are redundant in secondary walls (PMID:18980662, PMID:26043357).

IRX9/IRX14 GT43 components
irx9_irx14_components
Participant: Family: GT43 xylan synthase components (IRX9, IRX14)
Family:
GT43 xylan synthase components (IRX9, IRX14)
Representative Members: IRX9 (Arabidopsis)UniProtKB:Q9ZQC6 IRX14 (Arabidopsis)UniProtKB:Q8L707

Function

GT43 component of the xylan synthase complex Required GT43 partners of the IRX10 catalytic core. Loss of IRX14 with IRX14L nearly abolishes xylan, while irx9 irx9-L still makes a shorter-chain xylan (PMID:20424005); they are generally regarded as non-catalytic/structural components rather than independent xylosyltransferases, so no catalytic MF term is asserted for them here (the synthase activity, GO:0047517, is carried by the complex-level annoton).

Processes

plant-type secondary cell wall biogenesisGO:0009834

GT43 partners required for backbone synthesis; each is individually essential for normal xylan in Arabidopsis stems.

Variant set: Xylan synthase gene set by wall type by wall type / tissue (secondary vs primary cell wall) (One Or More)

The two Arabidopsis sets are paralogous and largely interchangeable when expressed in the same cells; they differ mainly in expression. Many tissues use both, hence ONE_OR_MORE.

Secondary-wall xylan synthase (IRX9/IRX10/IRX14)Protein Complexsecondary_wall_xsc

Main backbone synthase of xylem vessels and fibres. IRX9, IRX10 and IRX14 are the major secondary-wall genes; IRX9-L, IRX10-L and IRX14-L partly substitute for them (PMID:20424005).

Annotons

Secondary-wall xylan synthase activity
secondary_wall_xsc_activity
Participant: Protein Complex: Secondary-wall xylan synthase (IRX9/IRX10/IRX14)
Protein Complex:
Secondary-wall xylan synthase (IRX9/IRX10/IRX14)
Active units:
IRX10
Participant: Gene Product: IRX10 (Arabidopsis)
Gene Product:
IRX10 (Arabidopsis)UniProtKB:Q9FZJ1
Role: Catalytic GT47 xylosyltransferase.
IRX9
Participant: Gene Product: IRX9 (Arabidopsis)
Gene Product:
IRX9 (Arabidopsis)UniProtKB:Q9ZQC6
Role: GT43 component.
IRX14
Participant: Gene Product: IRX14 (Arabidopsis)
Gene Product:
IRX14 (Arabidopsis)UniProtKB:Q8L707
Role: GT43 component.

Function

1,4-beta-D-xylan synthase activityGO:0047517

Locations

Golgi membraneGO:0000139

Makes the glucuronoxylan backbone of secondary walls; its loss gives the irregular-xylem phenotype.

Primary-wall xylan synthase (IRX9L/IRX10L/IRX14)Protein Complexprimary_wall_xsc

Backbone synthase in primary-wall tissues (callus, seedlings), which makes a xylan with GlcA every six xylosyl residues that GUX3 decorates. irx9L, irx10L and irx14 single mutants lose this xylan, whereas irx9 and irx10 do not (PMID:26043357). IRX14 is shared with the secondary-wall set.

Annotons

Primary-wall xylan synthase activity
primary_wall_xsc_activity
Participant: Protein Complex: Primary-wall xylan synthase (IRX9L/IRX10L/IRX14)
Protein Complex:
Primary-wall xylan synthase (IRX9L/IRX10L/IRX14)
Active units:
IRX10L (XYS1)
Participant: Gene Product: IRX10L (Arabidopsis)
Gene Product:
IRX10L (Arabidopsis)UniProtKB:Q940Q8
Role: Catalytic GT47 xylan synthase.
IRX9L
Participant: Gene Product: IRX9L / IRX9H (Arabidopsis, At1g27600)
Gene Product:
IRX9L / IRX9H (Arabidopsis, At1g27600)UniProtKB:Q9SXC4
Role: GT43 component.
IRX14
Participant: Gene Product: IRX14 (Arabidopsis)
Gene Product:
IRX14 (Arabidopsis)UniProtKB:Q8L707
Role: GT43 component shared with the secondary-wall set.

Function

1,4-beta-D-xylan synthase activityGO:0047517

Locations

Golgi membraneGO:0000139

Makes the backbone of primary-wall xylan; irx10L callus membranes keep only traces of xylosyltransferase activity.

Part 2: reducing-end oligosaccharide sequence (eudicot) (optional)
Reducing-end oligosaccharide primer/terminatorMetabolic Pathwayreducing_end_sequence

Eudicot glucuronoxylan carries a distinctive reducing-end tetrasaccharide (Xyl-Rha-GalA-Xyl). IRX7/FRA8, IRX8/GAUT12, and PARVUS are required for its synthesis and for normal xylan chain amount/length; grasses lack this sequence.

Annotons

Reducing-end glycosyltransferases (FRA8/GAUT12/PARVUS)
reducing_end_gts
Participant: Family: xylan reducing-end glycosyltransferases
Family:
xylan reducing-end glycosyltransferases
Representative Members: IRX7 / FRA8 (Arabidopsis)UniProtKB:Q9ZUV3 GAUT12 / IRX8 (Arabidopsis)UniProtKB:Q9FH36 PARVUS / GATL1 (Arabidopsis)UniProtKB:Q9LN68

Function

reducing-end oligosaccharide glycosyltransfer Coordinated GT47/GT8 transfers building the Xyl-Rha-GalA-Xyl reducing-end sequence; exact per-enzyme linkage specificities are not asserted as single GO MF ids here.

Processes

glucuronoxylan biosynthetic processGO:0010417

Locations

Golgi apparatusGO:0005794

Synthesizes the eudicot reducing-end sequence proposed to prime or terminate the backbone; loss reduces xylan chain number.

Part 3: alpha-glucuronosyl sidechain addition
GlcA sidechain addition (GUX)Reactionglucuronosyl_substitution

Annotons

Xylan alpha-glucuronosyltransferase
gux_activity
Participant: Family: xylan alpha-(1,2)-glucuronosyltransferase (GUX)
Family:
xylan alpha-(1,2)-glucuronosyltransferase (GUX)
Representative Members: GUX1 (Arabidopsis)UniProtKB:Q9LSB1 GUX3 (Arabidopsis; primary-wall xylan)UniProtKB:Q8W4A7

Function

glucuronoxylan glucuronosyltransferase activityGO:0080116
Substrates: UDP-glucuronate (1->4)-beta-D-xylan backbone
Products: glucuronoxylan (GlcA-substituted) UDP

Locations

Golgi membraneGO:0000139

Adds (alpha-1,2)-glucuronic acid sidechains; the spacing/pattern of GlcA governs xylan-cellulose and xylan-lignin interactions.

Part 4: 4-O-methylation of the glucuronic acid sidechain (optional)
4-O-methylation of GlcA (GXM)ReactionglcA_methylation

Annotons

Glucuronoxylan 4-O-methyltransferase
gxm_activity
Participant: Family: glucuronoxylan 4-O-methyltransferase (GXM/DUF579)
Family:
glucuronoxylan 4-O-methyltransferase (GXM/DUF579)
Representative Members: GXM3 (Arabidopsis)UniProtKB:Q9LQ32

Function

glucuronoxylan 4-O-methyltransferase activityGO:0030775
Substrates: glucuronoxylan (GlcA) S-adenosyl-L-methionine
Products: glucuronoxylan (4-O-methyl-GlcA) S-adenosyl-L-homocysteine

Locations

Golgi apparatusGO:0005794

Methylates GlcA to 4-O-methyl-GlcA; the methyl:non-methyl GlcA ratio affects xylan solubility and lignin association.

Part 5: backbone O-acetylation
Xylan O-acetylation (ESK1/TBL29 + RWA acetyl supply)Metabolic Pathwayxylan_acetylation

O-acetyl esters on the xylose backbone (2-O and 3-O) are the most abundant xylan substituent and a major source of acetate that inhibits microbial fermentation of hydrolysates.

Part 1: xylan O-acetyltransfer
Xylan O-acetyltransferase (ESK1/TBL29)Reactionesk1_acetyltransfer

Annotons

Xylan O-acetyltransferase
esk1_activity
Participant: Family: TBL/DUF231 xylan O-acetyltransferase (ESK1/TBL29)
Family:
TBL/DUF231 xylan O-acetyltransferase (ESK1/TBL29)
Representative Members: ESK1 / TBL29 (Arabidopsis; XOAT1)UniProtKB:Q9LY46

Function

xylan O-acetyltransferase activityGO:1990538
Substrates: acetyl-CoA (or acetyl donor) (1->4)-beta-D-xylan backbone
Products: O-acetyl-xylan

Locations

Golgi membraneGO:0000139

Adds 2-O/3-O-acetyl esters to xylosyl residues; esk1 collapses xylem and reduces acetylation.

Part 2: Golgi acetyl-CoA supply (optional)
RWA acetyl donor supplyTransport Steprwa_acetyl_supply

Annotons

REDUCED WALL ACETYLATION (RWA) acetyl supply
rwa_activity
Participant: Family: RWA acetyl-CoA supply protein
Family:
RWA acetyl-CoA supply protein
Representative Members: RWA2 (Arabidopsis)UniProtKB:Q0WW17

Function

Golgi acetyl donor provision for wall O-acetylation RWA proteins supply the acetyl donor to the Golgi lumen for polysaccharide O-acetylation; exact transported species/MF is not asserted as a single GO id here.

Locations

Golgi membraneGO:0000139

Provides lumenal acetyl donor upstream of the O-acetyltransferases; rwa mutants have globally reduced wall acetylation.