Thesis presented March 22, 2022

Abstract:
In angiosperms, dark-grown seedlings are etiolated and non photosynthetic, containing only etioplasts. Upon light exposure, the photoreceptor phytochrome B (PHYB) is activated and eventually triggers in the nucleus photomorphogenesis that ends up with chloroplast biogenesis. At the molecular level, the transition from etioplast to chloroplast is accompanied by the reorganization of the plastid-encoded RNA polymerase (PEP) that interacts with twelve nuclear-encoded PEP-Associated Proteins (PAPs). Mutations in any PAP genes lead to chloroplasts deficiency: the plants remain albino and dye rapidly unless supplemented with a carbon source. PAP8 has a functional Nuclear Localization Signal (NLS), and is thus bi-localized both in chloroplasts and the nucleus. Moreover, PHYB signaling pathway is altered in pap8-1. First data from uncoupled localization of PAP8 show that the presence of PAP8 in the nucleus is necessary for the timing of chloroplast biogenesis during plant development. We therefore hypothesize that PAP8 may coordinate chloroplast biogenesis during plant development through a retrograde movement from plastid to nucleus. To investigate the question, we do complementation test with KOs plants with two mono-localized versions of PAP8, that are thus unable to shuffle between both organelles. The possible associated defects in the nucleus will be assessed by epi-fluorescence of PHYB-GFP tagged proteins and by the expression of photomorphogenetic genes in various mutants of PAP8.

Keywords:
Arabidopsis thaliana, Chloroplast biogenesis, Photomorphogenesis, Development, Echoprotein

On-line thesis.