Plant lectins: the ties that bind in root symbiosis and plant defense

Lectins are a diverse group of carbohydrate-binding proteins that are found within and associated with organisms from all kingdoms of life. Several different classes of plant lectins serve a diverse array of functions. The most prominent of these include participation in plant defense against predators and pathogens and involvement in symbiotic interactions between host plants and symbiotic microbes, including mycorrhizal fungi and nitrogen-fixing rhizobia. Extensive biological, biochemical, and molecular studies have shed light on the functions of plant lectins, and a plethora of uncharacterized lectin genes are being revealed at the genomic scale, suggesting unexplored and novel diversity in plant lectin structure and function. Integration of the results from these different types of research is beginning to yield a more detailed understanding of the function of lectins in symbiosis, defense, and plant biology in general

Modulation of Host Defence Systems

Arbuscular mycorrhizal (AM) fungi extensively invade host root tissues. This raises the question of how host plants contend with them; they must exert some kind of control over fungal proliferation since it is confined to a specific root tissue, the parenchymal cortex. Defence processes, which are triggered as a general plant response to microbial invasion, are modulated during root-fungus interactions in arbuscular mycorrhizas. This chapter presents an up-dated review of data on plant defence elicitation in these symbiotic systems and discusses possible mechanisms whereby defence reactions are maintained at a low level, as well as their implication in the phenomenon of bioprotection by AM fungi against soil-borne pathogens