Thesis
English
ID: <
10670/1.a2ckzt>
Abstract
The necessity to coordinate the expression of genes originating from different genomes within the plant cell resulted in the appearance of mechanisms imposing nuclear control over organelle gene expression. Anterograde signaling through sequence-specific trans-acting proteins (OTAFs) coexists in the chloroplast with an assembly dependent control of chloroplast synthesis (CES process) that coordinates the stoichiometric formation of photosynthetic complexes.Ribulose bisphosphate carboxylase/oxygenase (Rubisco) is a chloroplast-located carbon fixing enzyme constituted of two subunits. Large subunit (LSU) and small subunit (SSU) are encoded in the chloroplast and nuclear genomes respectively. In the stroma they assemble to form a hexadecameric holoenzyme (LSU8SSU8). In this study I tried to highlight major regulatory points of its synthesis in Chlamydomonas reinhardtii focusing on the posttranscriptional regulation of LSU.I showed that the MRL1 PPR protein is a limiting factor for rbcL mRNA accumulation. Whereas it has been previously designated as a stabilization factor for the abovementioned transcript, MRL1 appeared also to have a function in rbcL translation.Most notably, I have demonstrated that in Chlamydomonas reinhardtii Rubisco expression is controlled by the small subunit (SSU) presence. In its absence rbcL undergoes an inhibition of translation through its own product – the unassembled Rubisco large subunit. This process depends on LSU-oligomerization state as I was able to show that the presence of a high order LSU assembly intermediate bound to the RAF1 assembly chaperone is essential for the regulation to occur. In parallel I shed light on the fate of unassembled LSU in a deregulated CES context, thereby improving our understanding of the process of its folding and assembly.