The oligosaccharyltransferase subunit PsSTT3A regulates N-glycosylation and is critical for development and virulence of Phytophthora sojae.

In eukaryotes, N-glycosylation is a complex, multistep process in which the core subunit of oligosaccharyltransferase, Staurosporine and Temperature Sensitive 3A (STT3A), plays a critical role in the catalytic activity of the oligosaccharyltransferase (OST) complex. We found that the PsSTT3A gene plays a critical role in the viability of Phytophthora sojae (P. sojae). Furthermore, full PsSTT3A function was crucial to mycelial growth, sporangium production, zoospore production, and pathogenicity, as determined by gene silencing experiments. PsSTT3A is, itself, a highly N-glycosylated protein with six consensus NXS/T (Asn-X-Ser/Thr) motifs and one novel NS motif. However, the N-glycosylation sites on PsSTT3A that are required to support the development and virulence of P. sojae have been uncertain. Here, we demonstrated that glycosylation of site N593 is essential for normal mycelial growth and virulence in P. sojae. Furthermore, endoplasmic reticulum (ER) homeostasis was disrupted by the mutation of N593. N593A mutations reduced the stability of the elicitin PsSOJ2A, an N-glycoprotein, in gene replacement transformations. Our study reveals the functional significance of N-glycosylation of PsSTT3A in the development and infection cycles of P. sojae, demonstrating that targeting of PsSTT3A may be a promising strategy for developing new mode of action fungicides.