Metabolic Responses of Sugarcane Plants Upon Different Plant–Pathogen Interactions

Abstract

Sugarcane plants, subjected to environmental stress, mechanical injuries, or infection by pathogens, produce glycoproteins containing heterofructans, composed of a fairly extensive domain of β-1,2-fructofuranoside chains in which galactitol units intercalated. They could act as signaling molecules for cell recognition, able to discriminate between beneficial endophytes and bacterial or fungal pathogens. Infection mechanisms and disease progress are very different for different pathogens. Xanthomonas albilineans produces a gum, a xanthanlike polymer, which obliterates the xylem elements producing desiccation and leaf yellowing, and this disease has been termed “leaf scald.” Sporisorium scitamineum, on the other hand, uses stomata to penetrate the host tissues or secretes hydrolytic enzymes of cell wall polymers, which enable mycelial entry through any point on the surface of the plant. Pathogen spores also secrete quorum signals that increase the number of cells in the inoculum. However, some of the glycoproteins produced by infected cane act as false quorum signals. Then the probability of inhibiting germination increases by increasing the aggregation of the teliospores caused by noxious false signals. Alternatively, infection of sugarcane plants by smut teliospores elicits lignification by activating monolignol production. Lignin deposits increase in the cell walls of the infected plant and impede the entry of the pathogen. Teliospores must displace on the wet surface of the plant, either to find a natural way of entry or to be grouped by the effect of quorum sensing. The displacement occurs by successive contractions and relaxations of the actomyosin complex that composes the cytoskeleton.