The functional and structural characterization of <i>Xanthomonas campestris</i> pv. <i>campestris</i> core effector <scp>XopP</scp> revealed a new kinase activity

Abstract

SUMMARY Exo70B1 is a protein subunit of the exocyst complex with a crucial role in a variety of cell mechanisms, including immune responses against pathogens. The calcium‐dependent kinase 5 (CPK5) of Arabidopsis thaliana (hereafter Arabidopsis), phosphorylates At Exo70B1 upon functional disruption. We previously reported that, the Xanthomonas campestris pv. campestris effector XopP compromises At Exo70B1, while bypassing the host's hypersensitive response, in a way that is still unclear. Herein we designed an experimental approach, which includes biophysical, biochemical, and molecular assays and is based on structural and functional predictions, utilizing AplhaFold and DALI online servers, respectively, in order to characterize the in vivo Xcc XopP function. The interaction between At Exo70B1 and Xcc XopP was found very stable in high temperatures, while At Exo70B1 appeared to be phosphorylated at Xcc XopP‐expressing transgenic Arabidopsis. Xcc XopP revealed similarities with known mammalian kinases and phosphorylated At Exo70B1 at Ser107, Ser111, Ser248, Thr309, and Thr364. Moreover, Xcc XopP protected At Exo70B1 from At CPK5 phosphorylation. Together these findings show that Xcc XopP is an effector, which not only functions as a novel serine/threonine kinase upon its host target At Exo70B1 but also protects the latter from the innate At CPK5 phosphorylation, in order to bypass the host's immune responses. Data are available via ProteomeXchange with the identifier PXD041405.