PaASK1, a mitogen-activated protein kinase kinase kinase that controls cell degeneration and cell differentiation in Podospora anserina.
MAPKKK are kinases involved in cell signaling. In fungi, these kinases are known to regulate development, pathogenicity, and the sensing of external conditions. We show here that Podospora anserina strains mutated in PaASK1, a MAPKKK of the MEK family, are impaired in the development of crippled growth, a cell degeneration process caused by C, a nonconventional infectious element. They also display defects in mycelium pigmentation, differentiation of aerial hyphae, and making of fruiting bodies, three hallmarks of cell differentiation during stationary phase in P. anserina. Overexpression of PaASK1 results in exacerbation of crippled growth. PaASK1 is a large protein of 1832 amino acids with several domains, including a region rich in proline and a 60-amino-acid-long polyglutamine stretch. Deletion analysis reveals that the polyglutamine stretch is dispensable for PaASK1 activity, whereas the region that contains the prolines is essential but insufficient to promote full activity. We discuss a model based on the hysteresis of a signal transduction cascade to account for the role of PaASK1 in both cell degeneration and stationary-phase cell differentiation.
Kicka
Sébastien
S
Institut de Génétique et Microbiologie, Université de Paris XI, 91405 Orsay Cedex, France.
Silar
Philippe
P
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001203:Ascomycota / Q000201:enzymology*; D002454:Cell Differentiation / Q000235:genetics*; D003001:Cloning, Molecular; D017124:Conserved Sequence; D014644:Genetic Variation; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
D010455:Peptides; C097188:polyglutamine; D011392:Proline; D020930:MAP Kinase Kinase Kinases