Schematic diagram of conserved motifs and domains in the two major subfamilies of PC-PLD family. PXPH-PLDs (at the top) and C2-PLDs (at the bottom) differ principally in their N-terminal regions by presence of distinct phospholipid-binding domains, i.e. the PX and PH domains in the case of the PXPH-PLD subfamily, and the C2 domain in the case of the C2-PLD subfamily. Note that the support for presence of the PX domain in plant PXPH-PLDs was slighly below the default cutoff when searched with the Search Pfam tool. The same pays true for the PX domain in AtPLDp1 identified by SMART (see Materials and Methods). HKD boxes refer to catalytic motifs forming together single catalytic site in each protein. The PIP2 box in the PXPH-PLDs relates to a PIP2-binding motif, see the text and Fig. 4B.