Developmental Growth Control Exerted via the Protein A Kinase Tpk2 in 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.

Ashbya gossypii beyond industrial riboflavin production: A historical perspective and emerging biotechnological applications

“…However, the specific mechanisms of spore formation in A. gossypii are still poorly understood, not being clear whether there is a meiotic component to sporulation (Wasserstrom et al, 2013(Wasserstrom et al, , 2015. The A. gossypii reference strain ATCC10895 was found to harbor four identical mating-type cassettes in its genome containing MATa information, but no MAT orthologs were found (Dietrich et al, 2013;, which led to question the existence of a sexual cycle in this fungus .…”

“…8 starvation/filamentous growth response, and by the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway that governs all aspects of cell physiology, particularly morphogenesis, growth and sporulation (Wasserstrom et al, 2013(Wasserstrom et al, , 2015. However, the specific mechanisms of spore formation in A. gossypii are still poorly understood, not being clear whether there is a meiotic component to sporulation (Wasserstrom et al, 2013(Wasserstrom et al, , 2015.…”

The APSES protein Sok2 is a positive regulator of sporulation in Ashbya gossypii

“…When using CTS2 ‐downregulation (fourfold) as a cut off for genes downregulated by α2 , we identified 394 genes. In this gene set only about 10% of the genes were not found in the wild type sporulation gene set as previously defined (Wasserstrom et al ., ). The most striking of these genes was SOK2 , which was 13‐fold downregulated in the α2 strain, while it is mildly upregulated (4.5‐fold) in the wild type during sporulation and was, therefore, not included in the sporulation gene set of genes upregulated more than 5× under sporulation inducing conditions.…”

“…In our previous work we defined a central role of cAMP‐signaling and the Tpk2 protein kinase A for sporulation in A . gossypii (Wasserstrom et al ., ). Therefore, we decided to study the role of SOK2 for sporulation in A .…”

“…gossypii genome encodes about 500 sporulation specific genes. Expression of most of these genes is repressed by cAMP through the protein A kinase Tpk2 (Wasserstrom et al ., ).…”