The phocein homologue SmMOB3 is essential for vegetative cell fusion and sexual development in the filamentous ascomycete Sordaria macrospora

Abstract

Members of the striatin family and their highly conserved interacting protein phocein/Mob3 are key components in the regulation of cell differentiation in multicellular eukaryotes. The striatin homologue PRO11 of the filamentous ascomycete Sordaria macrospora has a crucial role in fruiting body development. Here, we functionally characterized the phocein/Mob3 orthologue SmMOB3 of S. macrospora. We isolated the gene and showed that both, pro11 and Smmob3 are expressed during early and late developmental stages. Deletion of Smmob3 resulted in a sexually sterile strain, similar to the previously characterized pro11 mutant. Fusion assays revealed that ∆Smmob3 was unable to undergo self-fusion and fusion with the pro11 strain. The essential function of the SmMOB3 N-terminus containing the conserved mob domain was demonstrated by complementation analysis of the sterile S. macrospora ∆Smmob3 strain. Downregulation of either pro11 in ∆Smmob3, or Smmob3 in pro11 mutants by means of RNA interference (RNAi) resulted in synthetic sexual defects, demonstrating for the first time the importance of a putative PRO11/SmMOB3 complex in fruiting body development.Electronic supplementary materialThe online version of this article (doi:10.1007/s00294-010-0333-z) contains supplementary material, which is available to authorized users.

A Fungal Sarcolemmal Membrane-Associated Protein (SLMAP) Homolog Plays a Fundamental Role in Development and Localizes to the Nuclear Envelope, Endoplasmic Reticulum, and Mitochondria

“…Many mutants impaired in sexual development are also impaired in vegetative hyphal fusion and vice versa, although this correlation is not strict (e.g., see references 27 and 60 to 62). Mutants lacking Sordaria STRIPAK components PRO11, PRO22, and SmMOB3 are also impaired in vegetative hyphal fusion (30,56). We thus assessed hyphal fusion in the ⌬pro45 mutant and complemented strains.…”

“…All Sordaria STRIPAK components characterized so far are involved in sexual development, i.e., the formation of sexual fruiting bodies (perithecia) (35,56,57). We therefore analyzed the pro45 deletion strain for defects in the sexual cycle.…”

Hyphal Fusion

“…Deletion of ham-2, ham-3, or ham-4 rendered the mutants anastomosis deficient (Simonin et al 2010), while sexual trichogyne-conidium fusion was unaffected. Similarly, S. macrospora mutants affected in the ham-2 and ham-3 homologs pro22 and pro11 exhibit deficiencies in vegetative hyphal fusion (Rech et al 2007;Bloemendal et al 2010;Bernhards and Poggeler 2011). Similar to yeast mating, germling fusion in N. crassa also seems to be accompanied by mitotic arrest .…”

“…The human homologs of ham-3 and ham-4 (striatin and SLMAP) are parts of the so-called STRIPAK complex, a large multiprotein assembly. Interestingly, homologs of another component of this complex -Mob3 -are also essential for hyphal fusion in N. crassa and S. macrospora (Maerz et al 2009;Bernhards and Poggeler 2011). SLMAP is essential for myoblast fusion during muscle development (Guzzo et al 2004), suggesting potential conserved functions from fungi to animals.…”

“…SLMAP is essential for myoblast fusion during muscle development (Guzzo et al 2004), suggesting potential conserved functions from fungi to animals. Based on studies in different systems, striatin complexes are thought to function as locally assembled signalosomes involved in the coordination of different signal transduction pathways (Bernhards and Poggeler 2011;Benoist et al 2006). …”