chitosan layer of spore wall

GO:0005631 · Spore · Envelope layer · Proposed

The second outermost layer of the spore wall, as described in Saccharomyces. [GO:0005631]

Part of: ascospore wall (GO:0005619)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
chitosan	Polysaccharide	part of	`CHEBI:16261`			ESSENTIAL	Deacetylated chitin polymer material that forms the Saccharomyces ascospore-wall layer between the inner mannan/glucan layers and the outer dityrosine layer. `DOI:10.1016/S0014-5793(99)01334-4` Christodoulidou et al. 1999 studied Cda1 and Cda2 chitin deacetylases and how their elimination affects Saccharomyces ascospore-wall assembly. `DOI:10.1128/MMBR.69.4.565-584.2005` Neiman 2005 reviews chitosan as the second outer Saccharomyces ascospore-wall layer.

Taxonomic distribution

NCBITaxon:4932 Saccharomyces cerevisiae — COMMON: Budding yeast builds a chitosan layer during ascospore-wall maturation; this first standalone record does not assert an identical layer throughout ascospore-forming fungi. [DOI:10.1128/MMBR.69.4.565-584.2005]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Budding-yeast model in which Cda1/Cda2-dependent chitin deacetylation is tied to ascospore-wall assembly and rigidity. [DOI:10.1016/S0014-5793(99)01334-4]

Functions

outer ascospore-wall maturation — The chitosan layer forms the deacetylated chitin-containing surface beneath the dityrosine layer and contributes to construction of a rigid mature Saccharomyces ascospore wall.
- DOI:10.1074/jbc.271.49.31420 Christodoulidou et al. 1996 identified two sporulation-specific chitin deacetylase genes required for Saccharomyces ascospore-wall rigidity.
- DOI:10.1371/journal.pgen.1003700 Lin et al. 2013 tested the redundant Saccharomyces gene network that controls outer spore-wall assembly.

Mechanism graphs

Chitin deacetylation produces the chitosan layer of the ascospore wall (ASSEMBLY)

In Saccharomyces cerevisiae, chitin deacetylases convert spore-wall chitin into chitosan, which forms the second outermost ascospore-wall layer between the inner layers and the dityrosine surface.

Subject	Predicate	Object	Evidence
Cda1/Cda2 chitin deacetylases	produce	chitosan	`DOI:10.1016/S0014-5793(99)01334-4` Christodoulidou et al. 1999 studied the Cda1 and Cda2 chitin deacetylases and their effects on Saccharomyces ascospore-wall assembly.
chitosan	forms	chitosan layer of spore wall	`GO:0005631` GO:0005631 identifies the complete chitosan layer as a Saccharomyces spore-wall structure. `CHEBI:16261` ChEBI:16261 identifies the chitosan polymer. `DOI:10.1128/MMBR.69.4.565-584.2005` Neiman 2005 reviews chitosan deposition as the Saccharomyces ascospore-wall layer between the inner wall and dityrosine layer.
chitosan layer of spore wall	overlies	inner layer of spore wall	`GO:0005631` GO:0005631 defines the chitosan layer as the second outermost Saccharomyces spore-wall layer. `GO:0005632` GO:0005632 defines the inner layers as the two innermost Saccharomyces spore-wall layers.
dityrosine layer of spore wall	overlies	chitosan layer of spore wall	`GO:0005630` GO:0005630 defines the dityrosine layer as the outermost Saccharomyces spore-wall layer. `GO:0005631` GO:0005631 places the chitosan layer immediately beneath the dityrosine layer. `DOI:10.1371/journal.pgen.1003700` Lin et al. 2013 studied genes controlling Saccharomyces outer spore-wall assembly.
chitosan layer of spore wall	is layer of	ascospore wall	`GO:0005631` GO:0005631 defines the chitosan layer as part of the Saccharomyces spore wall. `GO:0005619` GO places GO:0005631 as part of the ascospore wall.

Discussions

INTERPRETATION (RESOLVED): Use CHEBI:16261 for the chitosan polymer constituent, not for the complete chitosan layer structure. CHEBI:16261 denotes the source-neutral chitosan polymer, whereas GO:0005631 denotes the full Saccharomyces spore-wall layer made from chitosan.
INTERPRETATION (RESOLVED): Treat Chs3, Cda1, and Cda2 as chitosan-layer biosynthetic machinery rather than mature-layer constituents. Chs3 synthesizes chitin and Cda1/Cda2 modify chitin into chitosan for wall assembly, but the curated constituent is the resulting chitosan polymer rather than its biosynthetic enzymes.

Evidence

GO:0005631 Gene Ontology cellular-component term for the Saccharomyces spore-wall chitosan layer.
GO:0005619 Gene Ontology cellular-component term for the broader ascospore wall that contains the chitosan layer.
GO:0005632 Gene Ontology cellular-component term for the inner layers below the Saccharomyces chitosan layer.
GO:0005630 Gene Ontology cellular-component term for the dityrosine layer above the Saccharomyces chitosan layer.
CHEBI:16261 ChEBI term for chitosan.
DOI:10.1074/jbc.271.49.31420 Christodoulidou et al. 1996, Two Sporulation-specific Chitin Deacetylase-encoding Genes Are Required for the Ascospore Wall Rigidity of Saccharomyces cerevisiae, Journal of Biological Chemistry.
DOI:10.1016/S0014-5793(99)01334-4 Christodoulidou et al. 1999, Yeast Ascospore Wall Assembly Requires Two Chitin Deacetylase Isozymes, FEBS Letters.
DOI:10.1128/EC.3.6.1464-1475.2004 Coluccio et al. 2004, Morphogenetic Pathway of Spore Wall Assembly in Saccharomyces cerevisiae, Eukaryotic Cell.
DOI:10.1128/MMBR.69.4.565-584.2005 Neiman 2005, Ascospore Formation in the Yeast Saccharomyces cerevisiae, Microbiology and Molecular Biology Reviews.
DOI:10.1371/journal.pgen.1003700 Lin et al. 2013, A Highly Redundant Gene Network Controls Assembly of the Outer Spore Wall in S. cerevisiae, PLOS Genetics.

Curation history

2026-09-23T02:11:55Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T02:13:19Z codex · EXPANDED_RECORD — Added ascospore-wall parthood, a CHEBI-grounded chitosan component, Saccharomyces cerevisiae scope, an outer-wall maturation function, GO/DOI evidence, a nonmechanistic chitosan-layer assembly graph, and boundary discussions for the chitosan polymer and Chs3/Cda1/Cda2 enzymes.
2026-09-23T02:32:50Z codex · ADDRESS_REVIEW — Resolved PR #1344 review issue #1345 by adding direct Saccharomyces literature evidence to the chitosan-to-chitosan-layer formation edge.

Source: data/structures/spore/chitosan_layer_of_spore_wall.yaml