Den trasiga Sm-ringen : jakten på ursprunget till köldkänsligheten hos splitsningsmutanten SmE1 i A. thaliana

Temperature is an important signal that informs plants about their surroundings and daily and seasonal changes. In temperate climates, temperature variation throughout the year can reach up to 40°C, and usually, it is the cold that acts as a limiting factor for successful growth and development. The cold response is a multifaceted process that affects all levels of the organization, from molecular to organismal. There is an intertwined network of transcriptional changes, cold-triggered splicing events, and unspecific stress responses. The aim of this thesis was to investigate the role of PORCUPINE (PCP/SmE1), a component of the core splicing complex called Sm-ring, in cold signaling and its connection to co-occurring events in the model plant Arabidopsis thaliana. Despite the functional redundancy of PCP and its homolog PORCUPINE-LIKE (PCPL/SmE2), their roles diverge due to the differential gene regulation in response to temperature. We showed a correlation between the level of the PCP transcript and plant phenotype and linked PCP expression to its introns. Then, we compared the transcriptome of the knockout PCP mutant, pcp-1, to other temperature-sensitive splicing mutants and showed a pool of differential splicing events that were PCP-specific. Some of these events were linked to the core components of the cold response. We hypothesized that at least part of the pleiotropic effects of the PCP loss in A. thaliana occur due to the misregulated splicing of these genes. We also identified a plausible connection between splicing and transcription through PCP as a component of the Sm-ring and an RNA Polymerase II regulator, CDKC;2. Here we found that the loss of CDKC;2 in the pcp-1 background rescued the cold-sensitive pcp-1 phenotype and restored transcriptional kinetics to the wild-type levels. Finally, we hypothesize that a broken Sm-ring requires an appropriate attenuation of the transcription rates to perform the splicing successfully. Taken together, the work in this thesis demonstrates the complexity of the cold response mechanisms in A. thaliana and the central role of splicing components, such as PCP, for temperature acclimatization.