Root-knot nematode chemotaxis is positively regulated by l-galactose sidechains of mucilage carbohydrate rhamnogalacturonan-I

Root-knot nematodes (RKNs) are plant parasites and major agricultural pests. RKNs are thought to locate hosts through chemotaxis by sensing host-secreted chemoattractants; however, the structures and properties of these attractants are not well understood. Here, we describe a previously unknown RKN attractant from flaxseed mucilage that enhances infection of Arabidopsis and tomato, which resembles the pectic polysaccharide rhamnogalacturonan-I (RG-I). Fucose and galactose sidechains of the purified attractant were found to be required for attractant activity. Furthermore, the disaccharide α-l-galactosyl-1,3-l-rhamnose, which forms the linkage between the RG-I backbone and galactose sidechains of the purified attractant, was sufficient to attract RKN. These results show that the α-l-galactosyl-1,3-l-rhamnose linkage in the purified attractant from flaxseed mucilage is essential for RKN attraction. The present work also suggests that nematodes can detect environmental chemicals with high specificity, such as the presence of chiral centers and hydroxyl groups.