Kinase Inhibitor VvBKI1 Interacts with Ascorbate Peroxidase VvAPX1 Promoting Plant Resistance to Oomycetes.

Downy mildew caused by oomycete pathogen Plasmopara viticola is a devastating disease of grapevine. P. viticola secretes an array of RXLR effectors to enhance virulence. One of these effectors, PvRXLR131, has been reported to interact with grape ( Vitis vinifera ) BRI1 kinase inhibitor (VvBKI1). BKI1 is conserved in Nicotiana benthamiana and Arabidopsis thaliana . However, the role of VvBKI1 in plant immunity is unknown. Here, we found transient expression of VvBKI1 in grapevine and N. benthamiana increased its resistance to P. viticola and Phytophthora capsici , respectively. Furthermore, ectopic expression of VvBKI1 in Arabidopsis can increase its resistance to downy mildew caused by Hyaloperonospora arabidopsidis . Further experiments revealed that VvBKI1 interacts with a cytoplasmic ascorbate peroxidase, VvAPX1, an ROS-scavenging protein. Transient expression of VvAPX1 in grape and N. benthamiana promoted its resistance against P. viticola , and P. capsici . Moreover, VvAPX1 transgenic Arabidopsis is more resistant to H. arabidopsidis . Furthermore, both VvBKI1 and VvAPX1 transgenic Arabidopsis showed an elevated ascorbate peroxidase activity and enhanced disease resistance. In summary, our findings suggest a positive correlation between APX activity and resistance to oomycetes and that this regulatory network is conserved in V. vinifera , N. benthamiana , and A. thaliana .