Two Host Cytoplasmic Effectors Are Required for Pathogenesis of Phytophthora sojae by Suppression of Host Defenses    

Abstract

Phytophthora sojae encodes hundreds of putative host cytoplasmic effectors with conserved FLAK motifs following signal peptides, termed crinkling-and necrosis-inducing proteins (CRN) or Crinkler. Their functions and mechanisms in pathogenesis are mostly unknown. Here, we identify a group of five P. sojae-specific CRN-like genes with high levels of sequence similarity, of which three are putative pseudogenes. Functional analysis shows that the two functional genes encode proteins with predicted nuclear localization signals that induce contrasting responses when expressed in Nicotiana benthamiana and soybean (Glycine max). PsCRN63 induces cell death, while PsCRN115 suppresses cell death elicited by the P. sojae necrosisinducing protein (PsojNIP) or PsCRN63. Expression of CRN fragments with deleted signal peptides and FLAK motifs demonstrates that the carboxyl-terminal portions of PsCRN63 or PsCRN115 are sufficient for their activities. However, the predicted nuclear localization signal is required for PsCRN63 to induce cell death but not for PsCRN115 to suppress cell death. Furthermore, silencing of the PsCRN63 and PsCRN115 genes in P. sojae stable transformants leads to a reduction of virulence on soybean. Intriguingly, the silenced transformants lose the ability to suppress host cell death and callose deposition on inoculated plants. These results suggest a role for CRN effectors in the suppression of host defense responses.

Two Cytoplasmic Effectors of Phytophthora sojae Regulate Plant Cell Death via Interactions with Plant Catalases

“…We previously demonstrated that PsCRN63 and PsCRN115, although sharing high sequence similarity, have contrasting roles in manipulating plant PCD. Expression of PsCRN63 and PsCRN115 is jointly required for full virulence (Liu et al, 2011). Here, we show that expression of PsCRN63 or PsCRN63/115 together promotes the in planta growth of P. capsici.…”

“…5E), indicating that the suppression of PsCRN63-induced PCD by catalases is specific. We also noticed that PsCRN115 did not suppress PCD triggered by these inducers (Liu et al, 2011), indicating that the catalases and PsCRN115 are specifically involved in regulating the PCD-triggering activity of PsCRN63.…”

“…PsCRN63 and PsCRN115 are localized to the plant cell nucleus (Liu et al, 2011). However, catalases are usually enriched in the cytoplasm and peroxisomes (Mhamdi et al, 2010).…”

“…Silencing of PsCRN63/115 jointly reduced P. sojae virulence (Liu et al, 2011). To further determine the role of PsCRN63 and PsCRN115 during pathogen infection, we used an in planta transient assay.…”

“…Although sharing 95.7% identity at the amino acid level, they possess contrasting biological activities on N. benthamiana and soybean. Specifically, PsCRN63 induces PCD while PsCRN115 blocks it (Liu et al, 2011). The underlying mechanisms, however, remain unknown.…”