Contributes to histone modification (PubMed:16710447, PubMed:17967446, PubMed:20188723, PubMed:20555324, PubMed:21455483, PubMed:22012258). May position the N-terminus of histone H3 for efficient trimethylation at 'Lys-4' (PubMed:21455483). Required for di- and trimethylation, particularly for the trimethylation at 'Lys-4' of histone H3 (PubMed:20555324, PubMed:21455483, PubMed:24682813, PubMed:21527717). Not required for demethylation of histone H3 'Lys-27' (PubMed:21455483). H3 'Lys-4' methylation represents a specific tag for epigenetic transcriptional activation, germline establishment, maintenance and function (PubMed:21455483). Implicated in the epigenetic inheritance of lifespan over several generations (PubMed:22012258). Acts in the germline to limit the longevity of the soma, probably by regulating a lipid metabolism pathway that signals from the germline to the intestine, thereby preventing accumulation of mono-unsaturated fatty acids (PubMed:17967446, PubMed:20555324, PubMed:28379943). Required for RNA interference with probable antagonistic role against hpl-2 function (PubMed:17967446). Plays a role in vulval cell fate specification by acting in the synthetic multivulva pathway independent of set-2 (PubMed:17967446). Sex determining protein required in the germline to promote the spermatogenesis to oogenesis switch during the late larval stages of development (PubMed:24682813). Acts with the sex determining factor tra-1, and redundantly with wdr-5.2, to regulate fog-3 expression, which in turn determines germ cell fate (PubMed:24682813). Cooperates with jmjd-3.1, egl-27 and unc-3 to ensure robust transdifferentiation of the Y rectal cell to the PDA motor neuron during larval development (PubMed:25124442). Component of the SET2 complex (also known as the SET1/COMPASS complex), which contains at least set-2, swd-2.1, cfp-1, rbbp-5, wdr-5.1, dpy-30 and ash-2 (PubMed:31602465). Within the complex, interacts with cfp-1, ash-2, dpy-30 and hda-1 (PubMed:31602465). Interacts with histone H3 both unmethylated and methylated at 'Lys-4' (PubMed:21455483). Interacts with jmjd-3.1, ceh-6, sox-2, sem-4 and egl-27 (PubMed:25124442). Interacts with set-2 (PubMed:21527717). Localized on chromatin in the nucleus. Enriched in the germline (PubMed:17967446, PubMed:24682813). Detected in all nuclei of the embryo (PubMed:17967446). In larvae, expression is detected in the nuclei of seam cells, somatic gonad precursor cells Z1 and Z4, vulval precursor cells, distal tip cells, hypodermal cells, intestinal and muscle cells (PubMed:17967446). Also detected in the neurons from the ventral nerve cord, head and tail region (PubMed:17967446). Expressed in the head and tail region, intestinal cells, muscle cells, cells of the vulva, spermatheca and sheath cells in adults (PubMed:17967446). Detected from the 20 cell embryo stage and continues through to adult, although in a restricted manner. Increase in life span (PubMed:17967446). Longer time span to reach adulthood and reduced brood size resulting in sterility between generations F3 and F4 (PubMed:17967446). Associated embryonic lethality and additional somatic defects at elevated temperatures (PubMed:17967446). Defects in germ cells including defective sperm development and endomitotic oocytes (PubMed:17967446, PubMed:24682813). Significantly reduced H3 'Lys-4' trimethylation in both embryonic and adult germ cells in a sex-independent manner (PubMed:17967446). Increased fog-3 expression at 20 degrees Celsius (PubMed:24682813). At 20 and 25 degrees Celsius, double knockdown mutants with wdr-5.2 have increased fog-3 expression (PubMed:24682813). At 25 degrees Celsius, these mutants have increased wdr-5.2 and fog-1 expression, reduced brood size accompanied by 42% embryonic lethality with 100% of the surviving progeny being sterile (PubMed:24682813). Surviving progeny display enhanced defects in the spermatogenesis to oogenesis transition compared to the single wdr-5.1 knockout with 88% of the gonads only containing sperm (PubMed:24682813). The remaining germ cells in the gonads switch to oogenesis, but the oocytes display either an endoreplication or endomitotic phenotype (PubMed:24682813). Germ cells also have increased expression of the sex determining factor tra-1 in the cytoplasm and as a result there is reduced binding of tra-1 to the fog-3 promoter (PubMed:24682813). RNAi-mediated knockdown leads to an enrichment of mono-unsaturated fatty acids (PubMed:28379943). Belongs to the WD repeat WDR5/wds family.