Histone H3 Lys 4 methylation (H3K4me) is deposited by the conserved SET1/MLL methyltransferases acting in multiprotein complexes including Ash2 and Wdr5. While individual subunits contribute to complex activity, how they influence gene expression in a specific tissue remains largely unknown. In caenorhabditis elegans, SET-2/SET1, WDR-5.1 and ASH-2 are differentially required for germline H3K4 methylation. Using expression profiling on germlines from animals lacking
set-2,
ash-2 or
wdr-5.1, we show that these subunits play unique and redundant functions to promote expression of germline genes and repress somatic genes. We further show that in
set-2 and
wdr-5.1 deficient germlines, somatic gene misexpression is associated with conversion of germ cells into somatic cells, and that nuclear RNAi acts in parallel with SET-2 and WDR-5.1 to maintain germline identity. These findings uncover a unique role for SET-2 and WDR-5.1 in preserving germline pluripotency, and underline the complexity of the cellular network regulating this process.