Construction of a cassava PR protein-interacting network during Xanthomonas axonopodis pv. manihotis infection

Pathogenesis-related (PR) proteins are inducible antimicrobial defence proteins whose specific function in immunity or in other plant processes have not been deeply studied. Genes coding for PRs have been reported in different plant species with numerous homologous proteins belonging to the same functional protein family. Previously some PR candidate genes were identified in response to cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam): the genes for hevamine (HEV), chitinase (CHI) and sulphite reductase (SiR) were induced in a resistant cassava cultivar during the response to Xam. To understand their functional roles in defence responses, a protein-protein interaction map was generated based on yeast two-hybrid (Y2H) assays of these candidate PR proteins. The results showed that the cassava PRs interact with each other and, although hevamine and chitinase belong to the same class of chitinases, they share only four interactors. Co-regulated expression of PRs and their interactors was observed and similar ontology terms were identified for interactors. Furthermore, an overlap between immune and other metabolic pathways was noticed based on other bioinformatics studies. These results therefore shed more light on the possible function of PR proteins.