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Background  Polo-like kinases (PLKs) are conserved serine/threonine kinases that regulate the cell cycle. To date, the role of  Giardia lamblia  PLK (GlPLK) in cells has not been studied. Here, we report our investigation on the function of GlPLK to provide insight into the role of this PKL in  Giardia  cell division, especially during cytokinesis and flagella formation.    Methods  To assess the function of GIPLK,  Giardia  trophozoites were treated with the PLK-specific inhibitor GW843286X (GW). Using a putative open reading frame for the PLK identified in the  Giardia  genomic database, we generated a transgenic  Giardia  expressing hemagglutinin (HA)-tagged GlPLK and used this transgenic for immunofluorescence assays (IFAs). GlPLK expression was knocked down using an anti- glplk  morpholino to observe its effect on the number of nuclei number and length of flagella.  Giardia  cells ectopically expressing truncated GlPLKs, kinase domain + linker (GlPLK-KDL) or polo-box domains (GlPLK-PBD) were constructed for IFAs. Mutant GlPLKs at Lys51, Thr179 and Thr183 were generated by site-directed mutagenesis and then used for the kinase assay. To elucidate the role of phosphorylated GlPLK, the phosphorylation residues were mutated and expressed in  Giardia  trophozoites    Results  After incubating trophozoites with 5 μM GW, the percentage of cells with > 4 nuclei and longer caudal and anterior flagella increased. IFAs indicated that GlPLK was localized to basal bodies and flagella and was present at mitotic spindles in dividing cells. Morpholino-mediated GlPLK knockdown resulted in the same phenotypes as those observed in GW-treated cells .  In contrast to  Giardia  expressing GlPLK-PBD,  Giardia  expressing GlPLK-KDL was defective in terms of GIPLK localization to mitotic spindles and had altered localization of the basal bodies in dividing cells. Kinase assays using mutant recombinant GlPLKs indicated that mutation at Lys51 or at both Thr179 and Thr183 resulted in loss of kinase activity.  Giardia  expressing these mutant GlPLKs also demonstrated defects in cell growth, cytokinesis and flagella formation.    Conclusions  These data indicate that GlPLK plays a role in  Giardia  cell division, especially during cytokinesis, and that it is also involved in flagella formation.Supplementary Information  The online version contains supplementary material available at 10.1186/s13071-021-04687-5.

A polo-like kinase modulates cytokinesis and flagella biogenesis in Giardia lamblia