An apicoplast-localized deubiquitinase contributes to the cell growth and apicoplast homeostasis of Toxoplasma gondii

Toxoplasma gondii is among the most important parasites worldwide. The apicoplast is a unique organelle shared by all Apicomplexan protozoa. Increasing lines of evidence suggest that the apicoplast possesses its own ubiquitination system. Deubiquitination is a crucial step executed by deubiquitinase (DUB) during protein ubiquitination. While multiple components of ubiquitination have been identified in T. gondii , the deubiquitinases involved remain unknown. The aim of the current study was to delineate the localization of Tg OTU7 and elucidate its functions. Tg OTU7 was specifically localized at the apicoplast, and its expression was largely regulated during the cell cycle. Additionally, Tg OTU7 efficiently breaks down ubiquitin chains, exhibits linkage-nonspecific deubiquitinating activity and is critical for the lytic cycle and apicoplast biogenesis, similar to the transcription of the apicoplast genome and the nuclear genes encoding apicoplast-targeted proteins. Taken together, the results indicate that the newly described deubiquitinase Tg OTU7 specifically localizes to the apicoplast and affects the cell growth and apicoplast homeostasis of T. gondii .