A network involving Rho-type GTPases, a paxillin and a formin homologue regulates spore length and spore wall integrity in the filamentous fungus Ashbya gossypii

ABSTRACT Sporulation in Ashbya gossypii is induced by nutrient-limited conditions and leads to the formation of haploid spores. Using RNA-seq, we have determined a gene set induced upon sporulation, which bears considerable overlap with that of Saccharomyces cerevisiae but also contains A. gossypii -specific genes. Addition of cyclic AMP (cAMP) to nutrient-limited media blocks sporulation and represses the induction of sporulation specific genes. Deletion of the protein kinase A (PKA) catalytic subunits encoded by TPK1 and TPK2 showed reduced growth in tpk1 but enhanced growth in the tpk2 strain; however, both mutants sporulated well. Sporulation can be blocked by cAMP in tpk1 but not in tpk2 strains. Similarly, TPK2 acts at a second developmental switch promoting the break in spore dormancy. In S. cerevisiae , PKA phosphorylates and inhibits Msn2/4. The transcript profiles of the tpk1 and msn2/4 mutants were very similar to that of the wild type under sporulation conditions. However, deletion of the single A. gossypii MSN2/4 homolog generated a specific sporulation defect. We identified a set of genes involved in spore wall assembly that was downregulated in the msn2/4 mutant, particularly DIT2 , suggesting that poor spore viability may be due to lysis of spores. Our results reveal specific functional differences between the two catalytic PKA subunits in A. gossypii and identified Tpk2 as the key A kinase that transduces developmental decisions of growth. Our data also suggest that Msn2/4 is involved only at a late step of sporulation in A. gossypii and is not a major regulator of IME1 .

Download Full-text

Phosphoregulation provides specificity to biomolecular condensates in the cell cycle and cell polarity

The Journal of Cell Biology ◽

10.1083/jcb.201910021 ◽

2020 ◽

Vol 219 (7) ◽

Cited By ~ 2

Author(s):

Therese M. Gerbich ◽

Grace A. McLaughlin ◽

Katelyn Cassidy ◽

Scott Gerber ◽

David Adalsteinsson ◽

...

Keyword(s):

Cell Cycle ◽

Nucleic Acids ◽

Cell Polarity ◽

Filamentous Fungus ◽

Rna Binding ◽

Binding Protein ◽

Rna Binding Protein ◽

Ashbya Gossypii ◽

Mrna Targets ◽

Functional Identities

Biomolecular condensation is a way of organizing cytosol in which proteins and nucleic acids coassemble into compartments. In the multinucleate filamentous fungus Ashbya gossypii, the RNA-binding protein Whi3 regulates the cell cycle and cell polarity through forming macromolecular structures that behave like condensates. Whi3 has distinct spatial localizations and mRNA targets, making it a powerful model for how, when, and where specific identities are established for condensates. We identified residues on Whi3 that are differentially phosphorylated under specific conditions and generated mutants that ablate this regulation. This yielded separation of function alleles that were functional for either cell polarity or nuclear cycling but not both. This study shows that phosphorylation of individual residues on molecules in biomolecular condensates can provide specificity that gives rise to distinct functional identities in the same cell.

Download Full-text