Glycoside hydrolase family 5 gene Pp07886 in Pythium porphyrae: Identification, characterization, expression pattern, and activation of the host immunity

The oomycete Pythium porphyrae is a causative agent of red rot disease in the economically important alga Neopyropia yezoensis. However, little is known about the pathogenic mechanisms of P. porphyrae, although pathogenicity is known to involve glycoside hydrolases (GHs). GHs are involved in penetration of the host cell wall to allow oomycete invasion, as well as in nutrition and in counteracting the innate immune response of the host. In this study, a preliminary investigation of a GH5 family gene Pp07886 from P. porphyrae was performed. This gene was cloned from the P. porphyrae genome and phylogenetically identified as part of the GH5_23 subfamily. The recombinant Pp07886 (rPp07886) was found to be a polyspecific enzyme with xylanase and hesperidinase activity; thus, it might be involved in breaking down the algal cell wall and hydrolyzing hesperidin to counteract the host immune defenses. The qRT-PCR and western blot results showed that Pp07886 expression was strongly induced (187 to 1496 fold compared to vegetative mycelia) during the early infection stage (30 min to 1 day post inoculation). Furthermore, transcripts of Pp07886 were strongly induced by both xylan and hesperidin (4 and 9 fold compared to vegetative mycelia grown in SGG medium). Finally, rPp07886 was able to activate the expression of the host innate immune genes (20 to 702 fold compared to uninfected thalli cultured in PES seawater). These results suggested that Pp07886 was involved in early infection and induction of innate immunity in N. yezoensis. Thus, this research provided important data for further functional study of GH5 proteins in P. porphyrae, and increased the understanding of the molecular mechanism of pathogenicity of GH5 proteins in oomycetes.