The Function of the Coding Sequences for the Putative Pheromone Precursors in Podospora anserina Is Restricted to Fertilization

Abstract

We cloned the pheromone precursor genes of Podospora anserina in order to elucidate their role in the biology of this fungus. The mfp gene encodes a 24-amino-acid polypeptide finished by the CAAX motif, characteristic of fungal lipopeptide pheromone precursors similar to the a-factor precursor of Saccharomyces cerevisiae. The mfm gene encodes a 221-amino-acid polypeptide, which is related to the S. cerevisiae ␣-factor precursor and contains two 13-residue repeats assumed to correspond to the mature pheromone. We deleted the mfp and mfm coding sequence by gene replacement. The mutations specifically affect male fertility, without impairing female fertility and vegetative growth. The male defect is mating type specific: the mat؉ ⌬mfp and mat؊ ⌬mfm mutants produce male cells inactive in fertilization whereas the mat؊ ⌬mfp and mat؉ ⌬mfm mutants show normal male fertility. Genetic data indicate that both mfp and mfm are transcribed at a low level in mat؉ and mat؊ vegetative hyphae. Northern-blot analysis shows that their transcription is induced by the mating types in microconidia (mfp by mat؉ and mfm by mat؊). We managed to cross ⌬mfp ⌬mfm strains of opposite mating type, by complementation and transient expression of the pheromone precursor gene to trigger fertilization. These crosses were fertile, demonstrating that once fertilization occurs, the pheromone precursor genes are unnecessary for the completion of the sexual cycle. Finally, we show that the constitutively transcribed gpd::mfm and gpd::mfp constructs are repressed at a posttranscriptional level by the noncognate mating type.

Expression and Function of Sex Pheromones and Receptors in the Homothallic AscomyceteGibberella zeae

“…6). These results are similar to those obtained with P. anserina, in which the role of pheromones also is restricted to the fertilization step (11).…”

“…Deletion of either pheromone precursor gene caused male sterility of the corresponding mating type because spermatia could no longer attract female trichogynes (24). Similar results were obtained with pheromone deletion mutants of P. anserina (11) and C. parasitica (48).…”

“…Similarly, the full self-fertility of ⌬pre1 mutants and the partial self-fertility (ϳ50%) of ⌬pre2 mutants and ⌬pre1/⌬pre2 double mutants demonstrate that neither of the pheromone receptors is essential for female fertility. This pattern differs from the heterothallic ascomycetes N. crassa, P. anserina, and C. parasitica, in which pheromones and receptors are essential for fertilization (11,23,24,48). G. zeae also differs from the homothallic ascomycetes S. macrospora and E. nidulans, in which at least one functional pheromone receptor is required for self-fertilization (31,42).…”

“…There was only one candidate for pre1 in the genomic sequence, and it had the typical seven transmembrane domains of a G-protein-coupled receptor. Since ppg2 and pre1 homologs are functional in heterothallic ascomycetes (11,23,24), we hypothesize that the ppg2 and pre1 genes in G. zeae are nonfunctional vestiges of the evolutionarily recent change from a heterothallic to a homothallic life style in this fungus (49,50).…”

Pheromones Are Essential for Male Fertility and Sufficient To Direct Chemotropic Polarized Growth of Trichogynes during Mating in Neurospora crassa

“…The mature a-factor is highly hydrophobic due to prenylation at the cysteine residue, while the mature ␣-factor is hydrophilic and unmodified. These two classes of pheromone precursor genes have also been identified in several heterothallic filamentous ascomycetes, including Cryphonectria parasitica (50), Magnaporthe grisea (39), Podospora anserina (11), and Neurospora crassa (4,21), while only the MFarelated class has been found in basidiomycete fungi (5,31,44).…”