Cellular responses to long-term phosphate starvation of fission yeast: Maf1 determines fate choice between quiescence and death associated with aberrant tRNA biogenesis

Abstract

Inorganic phosphate is an essential nutrient acquired by cells from their environment. Here, we characterize the adaptative responses of fission yeast to chronic phosphate starvation, during which cells enter a state of quiescence, initially fully reversible upon replenishing phosphate after 2 days but resulting in gradual loss of viability during 4 weeks of starvation. Time-resolved analyses of changes in mRNA levels revealed a coherent transcriptional program in which phosphate dynamics and autophagy were upregulated, while the machineries for rRNA synthesis and ribosome assembly, and for tRNA synthesis and maturation, were downregulated in tandem with global repression of genes encoding ribosomal proteins and translation factors. Consistent with the transcriptome changes, proteome analysis highlighted global depletion of 102 ribosomal proteins. Concomitant with this ribosomal protein deficit, 28S and 18S rRNAs became vulnerable to site-specific cleavages that generated temporally stable rRNA fragments. The finding that Maf1, a repressor of RNA polymerase III transcription, was upregulated during phosphate starvation prompted a hypothesis that its activity might prolong lifespan of the quiescent cells by limiting production of tRNAs. Indeed, we found that deletion of maf1 results in precocious death of phosphate-starved cells via a distinctive starvation-induced pathway associated with tRNA overproduction and dysfunctional tRNA biogenesis.

Divergence of TORC1-mediated Stress Response Leads to Novel Acquired Stress Resistance in a Pathogenic Yeast

“…The ASR effect in C. glabrata bears similarity to a previously described stress resistance phenotype following chronic starvation in S. cerevisiae (Gresham et al 2011;Petti et al 2011;Carter-O'Connell et al 2012;Ebrahimi et al 2021;Garg et al 2023). Could the divergence in ASR be attributed to the difference in timing/threshold of the chronic starvation response?…”

Genetic and environmental determinants of multicellular-like phenotypes in fission yeast

“…Second, MLP formation can often take days to manifest, as is evident in our experiments and other work (25), while most measurements for stress or starvation responses are taken a few minutes to a few hours after induction (100,110–113). Future experiments with longer timepoints, covering colony-level responses on the order of days (74), and accounting for cell-to-cell heterogeneity (e.g. single-cell RNA-seq (114–116), and strain-to-strain variability (e.g.…”

“…Strikingly, even the 2 lab strains, JB22 and JB50, showed strong adhesion under phosphate starvation, while the adhesion level of JB759 was below the threshold in that condition (Fig2C).Additionally, JB50 exhibited flocculation when grown in EMM-P (Supp Fig3C). Indeed, a recent RNA-seq dataset from S. pombe lab strains grown under similar phosphate starvation conditions reveals that expression levels of the flocculation-related transcription factor gene mbx2 and downstream cell-adhesion genes increase with time under phosphate starvation(74) (Supp Fig 3D).Though not mentioned in that article, the authors confirmed that "cells started to clump together" under those conditions (Garg, Schwer, Shuman, personal communication). Lastly, comparing measurements across all conditions, we found that strains exhibiting strong adhesion generally featured lower colony density before washing (measured as decreased inverse pixel intensity), whichmay reflect a decreased growth rate (Permutation-based T-test: P<1E-5, Fig 2E, Supp Fig 3E).…”

Low‐Molecular Weight Compounds that Extend the Chronological Lifespan of Yeasts, Saccharomyces cerevisiae, and Schizosaccharomyces pombe

“…[5][6][7] In addition to the budding yeast Saccharomyces cerevisiae, the fission yeast Schizosaccharomyces pombe is an insightful eukaryotic model yeast for understanding cellular aging and lifespan. [8][9][10][11][12][13] Yeast lifespans can be defined in two ways as the replicative lifespan (RLS), as measured by the number of divisions a cell can divide during its lifetime, and as the chronological lifespan (CLS), indicating the survival period of a nondividing cell population, which is measured by viability after entry into the stationary phase. [14][15][16][17] The RLS is a model for the aging process of dividing cells (such as stem cells) in higher eukaryotes, whereas CLS is a model for the aging of nondividing cells (such as neurons) in higher eukaryotes.…”