Plasmodium, the causative agent of malaria, undergoes a remarkable transformation during its sexual stage to produce motile male gametes. Unlike model organisms,flagellar assemblyin Plasmodium is exceptionally unique: characterized by rapid assembly, violent beating, and an unconventional “basal body first, followed by axoneme” release pattern. Evolutionarily, Plasmodium has shed almost all classical basal body structures, trending toward an ultra-minimalist design. However, this raises a fundamental biological question: How does such a simplified structure prevent disintegration under the intense mechanical stress?
Recently, the research team led by Professor Yuan Jing from the School of Life Sciences of Xiamen University published a study in Current Biology titled “Mechanoregulation of basal body integrity during Plasmodium exflagellation”. The study identifies a specialized protein, Calcifer, which acts as a molecular shield allowing the minimalist basal body to resist extreme mechanical stress during male gametogenesis.
During Plasmodium male gametocyte exflagellation, the basal body faces a dual crisis. First, mature axonemes beat vigorously and quickly release from the cell body at a speed (294-1254 μm/h) that is orders of magnitude faster than axoneme outgrowth in model organisms. This process subjects the basal body to massive shear forces from beating and reactive forces from the cell membrane. Second, Plasmodium has lost the robust classical triplet microtubule structure, relying instead on fragile single microtubules. To understand how the parasite compensates for this structural vulnerability, the team identified the protein-Calcifer.
Gene knockout experiments showed that Plasmodium lacking Calcifer cannot produce fertile male gametes, completely blocking transmission to the mosquito. Calcifer deviates from classical basal body proteins in both localization and function: while classical proteins localize early to facilitate axoneme assembly, Calcifer is not associated with the basal body during axoneme assembly but translocates to this structure after assembly. Instead, its role is purely structural and protective.
Further experiments demonstrated that without Calcifer, the fully assembled axoneme disintegrates instantly upon release from the cell body, resulting in an abnormal "branching" flagellum. By knocking out the dynein gene (dhc1) to inhibit violent beating, the team was able to rescue the disintegration phenotype caused by Calcifer deficiency. Furthermore, 3D topological reconstruction revealed that Calcifer forms a sheath-like structure around the basal body, firmly locking the core components and the negative-end microtubules of the axoneme, ensuring structural integrity during the violent beating of exflagellation.
This study challenges the traditional understanding that basal body proteins primarily participate in nucleation and assembly. By defining Calcifer’s role in structural stabilization, the research not only provides a novel target for interventions to block malaria transmission but also expands our understanding of the functional diversity of basal bodies, offering a new evolutionary paradigm for how eukaryotic cells adapt to extreme physical challenges.
Professor Yuan Jing of Xiamen University is the corresponding author of the study. The study's co-first authors are Jiepeng Guan (PhD graduate) and Yujiao Gong (PhD student) from Xiamen University. Wenqi Liang (Master's graduate) from Xiamen University made significant contributions.
Paper link: https://www.cell.com/current-biology/fulltext/S0960-9822(26)00387-8
Commentary: https://www.cell.com/current-biology/fulltext/S0960-9822(26)00381-7
Cell press: https://www.thepaper.cn/newsDetail_forward_33079342
