The ecl family gene ecl3(+) is induced by phosphate starvation and contributes to sexual differentiation in fission yeast

In Schizosaccharomyces pombe, ecl family genes are induced by several signals, such as starvation of various nutrients, including sulfur, amino acids and Mg(2+), and environmental stress, including heat or oxidative stress. These genes mediate appropriate cellular responses and contribute to the maintenance of cell viability and induction of sexual differentiation. Although this yeast has three ecl family genes with overlapping functions, any environmental conditions that induce ecl3(+) remain unidentified. We demonstrate that ecl3(+) is induced by phosphate starvation, similar to its chromosomally neighboring genes, pho1(+) and pho84(+), which respectively encode an extracellular acid phosphatase and an inorganic phosphate transporter. ecl3(+) expression was induced by the transcription factor Pho7 and affected by the cyclin-dependent kinase (CDK)-activating kinase Csk1. Phosphate starvation induced G1 arrest and sexual differentiation via ecl family genes. Biochemical analyses suggested that this G1 arrest was mediated by the stabilization of the CDK inhibitor Rum1, which was dependent on ecl family genes. This study shows that ecl family genes are required for appropriate responses to phosphate starvation and provides novel insights into the diversity and similarity of starvation responses.