Required for oocyte nuclear envelope breakdown before entry of oocyte into spermatheca (PubMed:10660671). In meiotic cells, required for spindle dynamics and probably for spindle attachment to the chromosomes (PubMed:10660671). Zygotic role in the development of the germline and nerve cord (PubMed:10660671). In mitotic cells, plays a role in spindle organization and centrosome maturation (PubMed:20823068). Involved in asymmetric nuclear localization of cdc-25.1 during embryogenesis which affects cell division timing (PubMed:18305005, PubMed:18316412, PubMed:20823068). Together with plk-2, regulates cytoplasm polarity in early embryos (PubMed:18199581, PubMed:18316412, PubMed:18305005). May play a minor role in chromosome pairing and synapsis during oocyte meiosis I (PubMed:22018922). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with mex-5, mex-6 and spat-1. In mitosis, remains associated with centrosomes entering prophase through to anaphase. During metaphase, embryos show anterior enrichment and located to the chromosomes of the metaphase plate. In meiosis, detected at centrosomes after pronuclear meeting in post-meiotic 1-cell embryos. Associated with chromatin during chromosome segregation of anaphase and in the region between the dividing chromosomes. Cytoplasmic in mature, unfertilized oocytes (PubMed:10660671). Asymmetric cytoplasmic localization is regulated by mex-5 and mex-6 (PubMed:18199581, PubMed:18316412). Embryos. The POLO box domains are involved in the asymmetric cytoplasmic localization. Impaired protein polarity (PubMed:18316412, PubMed:20823068). Lengthened AB and P1 cell cycle times (PubMed:18316412, PubMed:20823068). RNAi-mediated knockdown causes defects in germline mitosis including cell-cylce arrest and formation of polyploid nuclei (PubMed:22018922). RNAi-mediated knockdown in plk-2 mutant background causes a loss in sun-1 phosphorylation at 'Ser-8' but not at 'Ser-12' (PubMed:22018922). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CDC5/Polo subfamily.