Growth, Differentiation and Sexuality

5 The Fungal Cell Wall
J.P. Latgé 1 ,R.Calderone 2
CONTENTS
I. Introduction ......................... 73
II. Cell Wall: Composition
and Organisation ...................... 74
A. TechniquestoStudyCellWall ......... 74
B. Composition and Fungal Evolution . . . . . 74
C. Structural Organisation of the Cell Wall . 77
III. Polysaccharide Biosynthesis ............. 80
A. Chitin............................ 80
1.ChitinSynthases.................. 80
2.RegulationofChitinSynthesis....... 82
3.Inhibition....................... 83
B. GlucanSynthesis ................... 83
1. β1,3GlucanSynthases ............. 83
a) Synthesis..................... 83
b) Regulation ................... 84
c) Inhibition.................... 85
2.OtherGlucans ................... 85
a) α1,3GlucanSynthesis........... 85
b) β1,6GlucanSynthesis........... 86
C. MannanSynthesis .................. 86
IV. Polysaccharide Remodelling ............. 87
A. PolysaccharideHydrolysis ............ 87
B. β1,3 Glucan Branching
and Cross-Linking Enzymes . . . . . . . . . . 88
V. Cell Wall Biosynthesis,
Environmental Stress
and Signal Transduction Pathways ........ 89
A. TheCellWallSalvagePathway......... 89
B. Signal Transduction Cascades Responsible
for Major Cell Wall Compensatory
Mechanisms....................... 90
1.TheHOGMAPKinasePathway...... 90
2.TheCellIntegrityPathway.......... 92
3. TOR and Calcineurin Signalling
Pathway ........................ 93
VI. Perspectives .......................... 94
References ........................... 95
I. Introduction
A thorough analysis of the biochemical organisation
and biogenesis of the fungal cell wall is essential
to obtain a good understanding of the growth
1 Aspergillus Unit, Institut Pasteur, 75015 Paris, France
2 Georgetown University, Washington, DC 20057, USA
of fungi in vitro and in their natural environment.
All exchanges between the fungal cell and its environment
rely upon a functional and permeable cell
wall. In plant and mammalian pathogens, the cell
wall is continuously in contact with the host, and
acts as a sieve and a reservoir for molecules such
as enzymes, antigens and elicitors or toxins which
play an active role during infection (Mouyna and
Latgé 2001). Moreover, it is essential to the resistance
of fungi to host defence reactions (Philippe
et al. 2003). The cell wall plays an essential role in
sensing adverse or favourable environments and,
particularly, it provides the fungus with adaptive
responses to variable osmotic pressures and other
stress factors. Fungi have developed cell wall repair
mechanisms which are rapidly activated following
damage to this structure (Klis et al. 2002).
Cell wall remodelling continuously occurs
during morphogenesis (Fig. 5.1). For example, in
moulds like Aspergillus fumigatus, the conidium
has a double-layered cell wall, the outer layer
Fig. 5.1. Cell wall modifications (synthesis and lysis) during
morphogenesis of yeasts and conidia
The Mycota I
Growth, Differentation and Sexuality
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© Springer-Verlag Berlin Heidelberg 2006