Yonggen Jia (Beijing / CN), Dr. Chaoyue Wang (Beijing / CN), Dr. Sari Kassem (Geneva / CH), Pei Sun (Beijing / CN), Alessandro Bonavoglia (Geneva / CH), Joachim Kloehn (Geneva / CH), Xianyong Liu (Beijing / CN), Professor Xun Suo (Beijing / CN), Professor Dr. Dominique Soldati-Favre (Geneva / CH)
The Myzozoa, a grouping of phyla within the Alveolates, emerged through endosymbiosis with a red alga, resulting in the acquisition of a plastid. This cluster includes Apicomplexa, Chromerida, Perkinsozoa, and Dinoflagellates, all sharing a notably reduced mitochondrial genome that encodes only three proteins for the mitochondrial electron transport chain, cytochrome c oxidase subunits 1 and 3 and cytochrome b. Intriguingly, the mitoribosomal rRNAs in these phyla exhibit high segmentation, prompting questions about the process of mitoribosome assembly.
Furthermore, these phyla possess four conserved proteins with domains resembling the plant Apetala2/ethylene response factor (AP2/ERF) integrase DNA binding domain. In Toxoplasma gondii, these four AP2 proteins localize within the mitochondrion and play a crucial role in oxidative phosphorylation and parasite viability. Surprisingly, instead of acting as transcription factors, these mtAP2s form tight interactions with the small and large mitoribosomal subunits. These genes are highly fitness-conferring and prove critical for mitoribosome assembly and integrity.
Applying mass spectrometry and small RNA sequencing to the purified T. gondii mitoribosome revealed its distinctive protein-rich composition, abundance of fragmented rRNAs, and assembly factors. Besides mtAP2s, other contributors, such as the RAP (RNA binding domain abundant in apicomplexans ) proteins, and HPR (heptatricopeptide repeat) proteins, contribute to molecular diversity and evolutionary adaptations. Together, our results provide insight into the composition, biogenesis and evolution of the ribosomal machinery in Alveolates.