Cold shock as a screen for genes involved in cold acclimatization in Neurospora crassa

Abstract

13When subjected to rapid drops of temperature (cold shock), Neurospora responds with a 14 dramatic, but temporary shift in its branching pattern. While the cold shock response has been 15 described morphologically, it has yet to be examined genetically. This project aims to begin the 16 genetic characterization of the cold shock response and the associated acclimatization to cold 17 environments. We report here the results of a screen of mutants from the Neurospora knockout 18 library for alterations in their morphological response to cold shock and thus, their ability to 19 acclimatize to the cold. Three groups of knockouts were selected to be subject to this screen: 20 genes previously suspected to be involved in hyphal development as well as knockouts resulting 21 in morphological changes; transcription factors; and genes homologous to E. coli genes known to showed altered cold shock responses in Neurospora -suggesting that the response in these two 26 organisms is largely shared in common. . CC-BY 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/259580 doi: bioRxiv preprint first posted online Feb. 4, 2018; 2 The environmental conditions that life must contend with can vary widely. Organisms have 1 evolved a wide range of mechanisms for contending with these changing conditions. For the 2 filamentous fungus Neurospora, growth continues through nearly the entire range of 3 temperatures (above freezing) that is observed in this environment. Although the rate of tip 4 extension varies linearly with temperature (Watters et al 2000), the branch density (the statistical 5 distribution of distances between branch sites along a linear growing hypha) remains constant 6 across this range (Watters et al. 2000) allowing the fungus to continue to infiltrate its 7 environment at the same density. Temperatures progressing through this range would be 8 expected to have dramatic impacts on enzyme activity generally (and thus overall metabolism), 9 but also directly on features critical to growth such as membrane fluidity, DNA/RNA stability 10 and the rates of transcription and translation. 12Response to cold shock 13 When the apparent independence of branching and temperature is tested by rapid temperature temperature, the colony returns to lateral branching, termed the "Recovery" phase. Growth in 22 this phase of the response resembles that which would be seen had the colony been grown at 4°C 23 continuously. The same density is observed for growth subjected to constant incubation at 4°C 24(or any other fixed temperature) as well (Watters et al 2000). Thus, the cold shock response 25 appears to be a temporary disturbance to a homeostatic system which maintains branch density at 26 a constant, evolutionarily favored, value. 28Thus, Neurospora appears to incorporate a system which has the effect of maintaining 29 homeostasis for critical cellular characteristics. At least one impact of this...