The protein Zucchini belongs to the phospholipase D (PLD) family of phosphodiesterases and has been implicated in promoting primary PIWI-interacting RNA (piRNA) biogenesis. PLD family members include both phospholipases and nucleases, but it has been unclear whether Zucchini has an impact on the piRNA biogenesis pathway indirectly (through a putative phospholipase activity) or directly (as a putative nuclease). Three recent reports address this question by analyzing mouse and Drosophila melanogaster Zucchini (mZuc and DmZuc, respectively) using structural and functional approaches. Ipsaro et al. determined the crystal structure of N-terminally truncated mZuc, whereas Nishimasu et al. and Voigt et al. solved the structure of an equivalent truncation of DmZuc. The papers demonstrate that Zucchini forms a dimer, with the active site assembled from conserved residues of both monomers, consistent with known monomeric and dimeric PLD protein structures. The mZuc structure contains an unexpected CCCH-type zinc-finger motif, which has been implicated in the binding of single-stranded RNA molecules, whereas DmZuc has a CHCC-type zinc-finger motif. In addition, the active site forms a narrow groove that can accommodate single-stranded, but not double-stranded, nucleic acids. Ipsaro et al. modeled a short RNA molecule into the structure of mZuc, illustrating the shape and charge complementarity provided by the RNA substrate. In support of the structural data, in vitro analyses confirmed that mZuc and DmZuc lacked any detectable phospholipase activity but instead demonstrated single-strand–specific nuclease activity. Nishimasu et al. further validated the functional significance of DmZuc's nuclease activity by demonstrating that wild-type dimeric DmZuc is critical for transposon silencing. mZuc and DmZuc cleavage generates 5′ phosphate and 3′ hydroxyl termini, which suggests that Zucchini might generate the 5′ ends of mature primary piRNAs, which are known to bear a 5′-monophosphate group. Future studies will be needed to pinpoint Zucchini's precise role in primary piRNA biogenesis. (Nature doi:10.1038/nature11502 and 10.1038/nature11509, published online 14 October 2012; RNA doi:10.1261/rna.034967.112, published online 19 October 2012)