ISBN 978-3-8439-4173-0

978-3-8439-4173-0, Reihe Biologie

Tobias Schenk
Investigation of light-induced SPA2 degradation and COP1-SPA inactivation in Arabidopsis thaliana

129 Seiten, Dissertation Universität Köln (2019), Softcover, B5

Zusammenfassung / Abstract

Light is the basis for photoautotrophic life on earth. It does not only provide the plants with energy, it is also an important source of information. Already during the process of germination, light exerts a great influence on the further development and the continuous growth of the plant. As a central repressor of photomorphogenesis, the COP1-SPA E3 ubiquitin ligase complex is responsible for the degradation of transcription factors, which are needed for a light response. The activity of the COP1-SPA complex is regulated by the interaction with photoreceptors, which contribute to the inactivation of the COP1-SPA complex. Overall, Arabidopsis thaliana has four SPA proteins, which have common, but also distinct functions in light signal transduction. In particular SPA2 was shown to be a powerful suppressor of photomorphogenesis in the dark and to be strong regulated when exposed to light. Already a brief irradiation of the seedling with light has the consequence that SPA2 is rapidly degraded, resulting in immediate inactivation of the COP1-SPA complex. It is assumed that the instability of SPA2 is caused by the interaction with the phytochrome photoreceptors and relies on the ubiquitination activity of COP1.

In the present work, it was found that the degradation of SPA2 depends on the higher order CULLIN4-based E3 ligase activity. In particular the CUL4COP10-DET1-DDB1 (CDD) complex revealed a great impact on SPA2 stability. Based on the idea to separate SPA2 from the CUL4-DDB1COP1-SPA, a new putative helical motif was identified in SPA2 that could mediate the interaction between DDB1 and SPA2.

Due to the fact that degradation of SPA2 is dependent on phytochrome A, phytochrome interaction sites in SPA2 were identified which may be responsible for SPA2 degradation. Transgenic lines lacking the N-terminus or the WD repeat of SPA2 demonstrated no degradation of the truncated protein in the light. Interestingly, the transgenic SPA2 line lacking the functional N-terminus of SPA2 exhibited a skotomorphogenic phenotype both in the dark and in light and almost lost the ability to perceive light.