Department of Cellular Biology, University of Georgia, Athens, Georgia, United States of America.
Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia, United States of America.
PLoS Biol. 2024 Sep 18;22(9):e3002801. doi: 10.1371/journal.pbio.3002801. eCollection 2024 Sep.
Malaria is a global and deadly human disease caused by the apicomplexan parasites of the genus Plasmodium. Parasite proliferation within human red blood cells (RBCs) is associated with the clinical manifestations of the disease. This asexual expansion within human RBCs begins with the invasion of RBCs by P. falciparum, which is mediated by the secretion of effectors from 2 specialized club-shaped secretory organelles in merozoite-stage parasites known as rhoptries. We investigated the function of the Rhoptry Neck Protein 11 (RON11), which contains 7 transmembrane domains and calcium-binding EF-hand domains. We generated conditional mutants of the P. falciparum RON11. Knockdown of RON11 inhibits parasite growth by preventing merozoite invasion. The loss of RON11 did not lead to any defects in processing of rhoptry proteins but instead led to a decrease in the amount of rhoptry proteins. We utilized ultrastructure expansion microscopy (U-ExM) to determine the effect of RON11 knockdown on rhoptry biogenesis. Surprisingly, in the absence of RON11, fully developed merozoites had only 1 rhoptry each. The single rhoptry in RON11-deficient merozoites were morphologically typical with a bulb and a neck oriented into the apical polar ring. Moreover, rhoptry proteins are trafficked accurately to the single rhoptry in RON11-deficient parasites. These data show that in the absence of RON11, the first rhoptry is generated during schizogony but upon the start of cytokinesis, the second rhoptry never forms. Interestingly, these single-rhoptry merozoites were able to attach to host RBCs but are unable to invade RBCs. Instead, RON11-deficient merozoites continue to engage with RBC for prolonged periods eventually resulting in echinocytosis, a result of secreting the contents from the single rhoptry into the RBC. Together, our data show that RON11 triggers the de novo biogenesis of the second rhoptry and functions in RBC invasion.
疟疾是一种由疟原虫属的顶复门寄生虫引起的全球性致命人类疾病。疟原虫在人类红细胞（RBC）内的增殖与疾病的临床表现有关。这种在人类 RBC 内的无性繁殖始于恶性疟原虫对 RBC 的入侵，这是由 2 种特殊的棒状分泌细胞器中的效应物分泌介导的，这 2 种细胞器在裂殖子阶段的寄生虫中被称为棒状体。我们研究了 Rhoptry Neck Protein 11（RON11）的功能，RON11 包含 7 个跨膜结构域和钙结合 EF 手结构域。我们生成了疟原虫 RON11 的条件突变体。RON11 的敲低抑制了寄生虫的生长，防止了裂殖体的入侵。RON11 的缺失并没有导致棒状体蛋白的加工缺陷，而是导致棒状体蛋白的数量减少。我们利用超微结构扩展显微镜（U-ExM）来确定 RON11 敲低对棒状体生物发生的影响。令人惊讶的是，在 RON11 缺失的情况下，完全成熟的裂殖子每个只有 1 个棒状体。RON11 缺陷的裂殖子中的单个棒状体在形态上是典型的，有一个球和一个朝向顶端极环的颈部。此外，棒状体蛋白在 RON11 缺陷寄生虫中准确地运输到单个棒状体。这些数据表明，在 RON11 缺失的情况下，第一个棒状体是在裂殖体期间产生的，但在胞质分裂开始时，第二个棒状体从未形成。有趣的是，这些单棒状体裂殖子能够附着在宿主 RBC 上，但不能入侵 RBC。相反，RON11 缺陷的裂殖子继续与 RBC 长时间接触，最终导致红细胞形态异常，这是由于将单个棒状体中的内容物分泌到 RBC 中所致。总之，我们的数据表明，RON11 触发了第二个棒状体的从头生物发生，并在 RBC 入侵中发挥作用。
