tRNA production links nutrient conditions to the onset of sexual differentiation through the TORC 1 pathway

Abstract

Target of rapamycin (TOR) kinase controls cell growth and metabo-lism in response to nutrient availability. In the fission yeast Schizosaccharomyces pombe, TOR complex 1 (TORC1) promotes vegetative growth and inhibits sexual differentiation in the pres-ence of ample nutrients. Here, we report the isolation and charac-terization of mutants with similar phenotypes as TORC1 mutants, in that they initiate sexual differentiation even in nutrient-rich conditions. In most mutants identified, TORC1 activity is downreg-ulated and the mutated genes are involved in tRNA expression or modification. Expression of tRNA precursors decreases when cells undergo sexual differentiation. Furthermore, overexpression of tRNA precursors prevents TORC1 downregulation upon nitrogen starvation and represses the initiation of sexual differentiation. Based on these observations, we propose that tRNA precursors operate in the S. pombe TORC1 pathway to switch growth mode from vegetative to reproductive.