Basic leucine zipper (bZIP) transcription factors are present exclusively in eukaryotes and constitute one of the largest and most diverse transcription factor families.The proteins are responsible for central developmental and physiological processes in plants, animals, and fungi, including the pathogenicity of fungal plant pathogens.However, there is limited understanding of bZIPs in oomycetes, which are fungus-like organisms in the kingdom Stramenopila.Oomycetes include many destructive plant pathogens, including the well-studied species Phytophthora sojae, which causes soybean stem and root rot.Candidate bZIPs encoded in the genomes of P.sojae and four other oomycetes, two diatoms, and two fungal species were predicted using bioinformatic methods.Comparative analysis revealed expanded numbers of bZIP candidates in oomycetes, especially the Phytophthora species, due to the expansion of several novel bZIP classes whose highly conserved asparagines in basic DNA-binding regions were substituted by other residues such as cysteine.The majority of these novel bZIP classes were mostly restricted to oomycetes.