Xanthomonas phaseoli pv. manihotis effector XopAO1 targets two key proteins to suppress defense in Cassava

Abstract

The Type Three Effector (TTE) protein AvrRpm1 of Pseudomonas syringae can contribute to pathogen virulence or induce an immune response in Arabidopsis, tomato, lettuce, and soybean by modifying their intracellular "guardee" plant protein, for example, AtRIN4. This triggers a resistance protein to halt pathogen proliferation. Other TTEs can directly interact with their host targets to bypass the plant immunity. Prior studies showed that Xanthomonas phaseoli pv. manihotis (Xpm), the causal agent of Cassava Bacterial Blight (CBB), uses the effector XopAO1 to suppress host Effector Triggered Immunity (ETI) and PAMP-triggered Immunity (PTI). Here, we used a yeast two-hybrid system and bioinformatic characterisation of two casava proteins and XopAO1 to investigate putative interactions involved in the development of CBB disease. Our results suggest that XopAO1 interacts with MeRIN4 and MeKinase full-length proteins. Also, we speculate that the XopAO1-MeRIN4 interaction is mediated by the ADP-ribosyl polymerase (PARP) domain in the N-terminal region of XopAO1, but domain-specific experimental interaction assays are needed. We also hypothesize that PARP-domain of XopAO1 might target either the C-NOI or the N-NOI domain of MeRIN4. Conversely, we determined that MeKinase harbours a protein kinase and NAF domains. At this point, we do not know the immunological consequences of XopAO1-MeKinase interaction, thus, further research will be required to elucidate this phenomenon.