A Valsa mali Effector Protein 1 Targets Apple (Malus domestica) Pathogenesis-Related 10 Protein to Promote Virulence

Abstract

To successfully colonize the plants, the pathogenic microbes secrete a mass of effector proteins which manipulate host immunity. Apple valsa canker is a destructive disease caused by the weakly parasitic fungus Valsa mali. A previous study indicated that the V. mali effector protein 1 (VmEP1) is an essential virulence factor. However, the pathogenic mechanism of VmEP1 in V. mali remains poorly understood. In this study, we found that the apple (Malus domestica) pathogenesis-related 10 proteins (MdPR10) are the virulence target of VmEP1 using a yeast two-hybrid screening. By bimolecular fluorescence (BiFC) and coimmunoprecipitation (Co-IP), we confirmed that the VmEP1 interacts with MdPR10 in vivo. Silencing of MdPR10 notably enhanced the V. mali infection, and overexpression of MdPR10 markedly reduced its infection, which corroborates its positive role in plant immunity against V. mali. Furthermore, we showed that the co-expression of VmEP1 with MdPR10 compromised the MdPR10-mediated resistance to V. mali. Taken together, our results revealed a mechanism by which a V. mali effector protein suppresses the host immune responses by interfering with the MdPR10-mediated resistance to V. mali during the infection.

Valsa mali secretes an effector protein VmEP1 to target a K homology domain‐containing protein for virulence in apple

“…However, the interaction between VmEP1 and MdPR10, a target protein of VmEP1 (Wang et al, 2021), did not result in degradation of MdPR10 (Figure S2), indicating that VmEP1 specifically promotes MdKRBP4 degradation. These results indicate that the interaction between VmEP1 and MdKRBP4 reduces MdKRBP4 accumulation by promoting its degradation.Previous studies have shown that VmEP1 interacts with MdPR10, an immune-related protein(Wang et al, 2021). In the present study,…”

“…Meanwhile, the expression levels of ROS accumulation-regulating genes (Figure 2c) and salicylic acid pathway-related genes, such as MdPR1, MdPR2, and MdPR5 (Figure 2d), were considerably enhanced 3 days post-infiltration. The relative transcript level of MdPR10, a target of VmEP1 (Wang et al, 2021), was also enhanced in apple leaves expressing MdKRBP4 (Figure 2d). These results suggest that the transient expression of MdKRBP4 activates the plant immune response and induces ROS accumulation.…”

“…In our previous study, the secretory protein VmEP1, with no known function, was shown to suppress plant defence by interrupting MdPR10-mediated resistance against V. mali (Wang et al, 2021).…”

“…However, the mechanism by which VmEP1 manipulates plant immunity is not known. Previously, we found that VmEP1 targeted MdPR10 (Wang et al, 2021) and other host proteins, such as KH domain-containing protein HEN4-like (MdKRBP4). In the present study, we discovered that VmEP1 interacts with MdKRBP4 and promotes the degradation of MdKRBP4.…”

“…The ascomycete Valsa mali , which causes apple ( Malus domestica ) Valsa canker, secretes effector protein 1 (VmEP1) to inhibit BAX‐induced programmed cell death (Li et al, 2015 ) and targets host pathogenesis‐related protein 10 (PR10) (Wang et al, 2021 ). However, the mechanism by which VmEP1 manipulates plant immunity is not known.…”