Insights into the formation of the Toxoplasma plant-like vacuolar compartment

During intracellular replication, Toxoplasma ingests and digests proteins derived from the cytosol of infected host cells. These ingested host proteins are transported to a specialized lysosome-like organelle known as the plant-like vacuolar compartment (PLVAC). Disrupting protein degradation within the PLVAC or the export of degradative products significantly attenuates both the acute and chronic stages of Toxoplasma infection. The PLVAC is strikingly dynamic. Whereas the it is usually a single entity in extracellular or newly invaded parasites, PLVAC undergoes sequential rounds of fission (fragmentation) and fusion (reformation) during intracellular replication. However, molecular mechanisms underlying this dynamic behavior remain unknown. To address this, we isolated the PLVAC by organellar pulldown and identified a Qbc-SNARE called TgSNAP29. Although TgSNAP29 was previously implicated in trafficking to the apicoplast, we found that TgSNAP29 predominantly localizes with the PLVAC and is essential for both the biogenesis of the PLVAC and parasite viability. Additionally, IP-MS/MS analysis of TgSNAP29 identified an R-SNARE protein, TgVAMP7, which also localizes to the PLVAC. Interestingly, although the PLVAC appeared normal in parasites lacking TgVAMP7, we found that these KO parasites markedly upregulated a closely related R-SNARE, TgVAMP8, suggesting a compensatory effect. Together these studies have opened a new avenue toward understanding how the PLVAC is formed and dynamically reformed during the parasite cell cycle. Future work will identify other novel players that are critical for PLVAC dynamics and biogenesis along with assessing the role of such processes during the chronic stage of infection.