Growth, Differentiation and Sexuality

320 R. Debuchy and B.G. Turgeon
be noted that the A IIRIP phenotype was attributed
to a transcription extinction of mat A-2 and mat
A-3.Averylowleveloftranscriptionofoneofthese
two genes cannot be ruled out and may contribute
to the formation of a few asci. For these reasons, we
would suggest that the A IIRIP and SMR1 − mutant
alleles are in one and the same pathway. SMR1 is
required each time a biparental progeny is formed,
namely, each time two different nuclei of opposite
mating type recognize each other. It is supposed
that SMR1 biological function is to overcome the
developmental arrest resulting from internuclear
recognition, and to regulate the differentiation of
the biparental ascogenous hyphae (Fig. 15.9).
VI. Conclusion
The past several years have seen a rapid rise in the
number of cloned and characterized mating-type
loci from an ever-expanding group of filamentous
Ascomycetes. However, the available mating-type
gene database still lacks some representatives of
functionally or taxonomically important groups.
No complete mating-type sequences are available
for the Euascomycetes that undergo mating-type
switching, or for lichen-forming fungi. The analysis
of the evolution of mating types is at the beginning,
focusing first on the evolutionary relationship
between self-compatible and self-incompatible
species from the same genus. A comparative
evolutionary history of the mating-type loci of
organisms with more distant connections, such
as those of Candida albicans, N. crassa, and
Cryptococcus neoformans,willrequiremucheffort
to be understood. Finally, investigations into the
role of mating-type proteins during development
of the fruiting body must be scaled up. The major
challenge in the mating-type field is to identify the
target genes of the mating-type transcription factors,
and to determine the function of these target
genes, as well as the function of the MAT1-1-2 and
MAT1-1-4 proteins themselves. Until recently, this
topic was limited due to intractable difficulties with
genetical approaches, or tedious and uncertain
molecular methods for finding target genes. Now,
entire genomes are available for all model systems,
and microarrays have been made or are under
construction for most of them. Whole-genome
methods will accelerate the discovery of target
genes, provided that microarray strategies include
careful selection of the mutants to be profiled,
to avoid including candidate genes not related to
mating-type function.
Acknowledgements. We are grateful to Shun-Wen Lu, Paul
Dyer, Tsutomu Arie, and Patrik Inderbitzin for communicating
results prior to publication. We thank Eiji Yokoyama
for discussions about Cordyceps takaomontana mating
types. Sequence data of Neurospora crassa, Chaetomium
globosum, Fusarium graminearum, Magnaporthe grisea
and Aspergillus nidulans were obtained from the Broad
Institute (http://www.broad.mit.edu/resources.html). Sequence
data of Podospora anserina were obtained from the
Podospora Genome project (http://podospora.igmors.upsud.fr/).
Annotation of P. anserina and C. globosum genes
presented in Fig. 15.3 was performed with FGENESH from
Softberry. Subcellular localization of proteins was predicted
with PSORT II (http://psort.nibb.ac.jp/form2.html). R.
Debuchy is very indebted to Evelyne Coppin for helpful
comments on this manuscript, and to Olivier Lespinet for
phylogenetic analyses.
References
Altschul SF, Madden TL, Schaffer AA, Zhang J, Zhang Z,
Miller W, Lipman DJ (1997) Gapped BLAST and PSI-
BLAST: a new generation of protein database search
programs. Nucleic Acids Res 25:3389–3402
Arie T, Kaneko I, Yoshida T, Noguchi M, Nomura Y,
Yamaguchi I (2000) Mating-type genes from asexual
phytopathogenic ascomycetes Fusarium oxysporum
and Alternaria alternata. Mol Plant Microbe Interact
13:1330–1339
Arnaise S, Zickler D, Glass NL (1993) Heterologous expression
of mating-type genes in filamentous fungi. Proc
Natl Acad Sci USA 90:6616–6620
Arnaise S, Coppin E, Debuchy R, Zickler D, Picard M (1995)
Models for mating type gene functions in Podospora
anserina. Fungal Genet Newslett Suppl 42:79
Arnaise S, Debuchy R, Picard M (1997) What is a bona fide
mating-type gene? Internuclear complementation of
mat mutants in Podospora anserina. Mol Gen Genet
256:169–178
Arnaise S, Zickler D, Le Bilcot S, Poisier C, Debuchy R (2001)
Mutations in mating-type genes of the heterothallic
fungus Podospora anserina lead to self-fertility. Genetics
159:545–556
Badgett TC, Staben C (1999) Interaction between and transactivation
by mating type polypeptides of Neurospora
crassa. Fungal Genet Newslett Suppl 46:73
Barve MP, Arie T, Salimath SS, Muehlbauer FJ, Peever TL
(2003) Cloning and characterization of the mating
type (MAT)locusfromAscochyta rabiei (teleomorph:
Didymella rabiei) andaMAT phylogeny of legumeassociated
Ascochyta spp. Fungal Genet Biol 39:151–
167
Beatty NP, Smith ML, Glass NL (1994) Molecular characterization
of mating-type loci in selected homothallic
species of Neurospora, Gelasinospora and Anixiella.
Mycol Res 98:1309–1316
Bennett RS, Yun SH, Lee TY, Turgeon BG, Arseniuk E, Cunfer
BM, Bergstrom GC (2003) Identity and conservation
of mating type genes in geographically diverse