Overexpression of an apple broad range agglutinating lectin does not promotein plantaresistance to fire blight and bacterial wilt

Abstract

AbstractLectins, a large group of proteins present in all kingdoms of life can bind reversibly to glycans. The roles of plant lectins are diverse and include resistance to biotic or abiotic stress, notably bacterial resistance. A gene family encoding amaranthin-like lectins termed MdAGGs in apple (Malus domestica) has been identified to be overexpressed upon treatment with the plant resistance inducer acibenzolar-S-methyl (ASM) which promotes enhanced resistance to the fire blight disease caused byErwinia amylovora(Ea). In this study, we first screened the ability of purified MdAGG10 to agglutinate bacterial cellsin vitroamong a range of bacterial species. Several bacterial species, either Gram positive or negative, either plant- or human-pathogens were found to be agglutinated by MdAGG10 in acidic conditions. Apple and Arabidopsis lines constitutively overexpressingMdAGG10were generated and evaluated for their resistance to, respectively,EaandRalstonia solanacearum, both plant pathogens that were found in our screening. Despite MdAGG10 protein accumulated in tissues of both apple and Arabidopsis lines, they remained susceptible to their respective pathogens. Interestingly,in vitroagglutination ofEaby MdAGG10 did not impair bacterial growth, suggesting that other plant molecules are involved in the resistance to fire blight triggered after an ASM treatment.