RNA binding proteins mediate the ability of a fungus to adapt to the cold

Abstract

Little is known about how fungi adapt to chilling. In eubacteria, cold shock proteins (CSPs) facilitate translation by destabilizing RNA secondary structure. Animals and plants have homologous cold shock domains within proteins, and additional glycine-rich RNA binding proteins (GRPs), but their role in stress resistance is poorly understood. In this study, we identified GRP homologues in diverse fungi. However, only Aspergillus clavatus and Metarhizium anisopliae possessed cold shock domains. Both M. anisopliae's small eubacteria-like CSP (CRP1) and its GRP (CRP2) homologue were induced by cold. Disrupting either Crp1 or Crp2 greatly reduced metabolism and conidial germination rates at low temperatures, and decreased tolerance to freezing. However, while both Crp1 and Crp2 reduced freezing-induced production of reactive oxygen species, only Crp1 protected cells against H(2)O(2) and increased M. anisopliae's virulence to caterpillars. Unlike CRP2, CRP1 rescued the cold-sensitive growth defects of an Escherichia coli CSP deletion mutant, and CRP1 also demonstrated transcription anti-termination activity, so CRP1 can regulate transcription and translation at low temperature. Expressing either Crp1 or Crp2 in yeast increased metabolism at cold temperatures and Crp1 improved tolerance to freezing. Thus besides providing a model relevant to many biological systems, Crp1 and Crp2 have potential applications in biotechnology.