Identification of Naturally Occurring Polyamines as Root-Knot Nematode Attractants

Root-knot nematodes(RKNs;genus Meloidogyne)are a class of plant parasites that infect the roots of many plant species.It is believed that RKNs target certain signaling molecules derived from plants to locate their hosts;however,currently,no plant compound has been unambiguously identified as a universal RKN attractant.To address this question,we screened a chemical library of synthetic compounds for Meloidogyne incognita attractants.The breakdown product of aminopropylam ino-anthraquinone,1,3-diam inopropane,as well as its related compounds,putrescine and cadaverine,were found to attract M.incognita.After exam ining various polyamines,M.incognita were found to be attracted specifically by natural com pounds that possess three to five methylene groups between two terminal amino groups.Using cryo-TO F-SIM S/SEM,cadaverine was indeed detected in soybean root cortex cells and the surrounding rhizosphere,establishing a chemical gradient.In addition to cadaverine,putrescine and 1,3-diam inopropane were also detected in root exudate by HPLC-MS/MS.Furtherm ore,exogenously applied cadaverine is sufficient to enhance M.incognita infection of Arabidopsis seedlings.These results suggest that M.incognita is likely attracted by polyam ines to locate the appropriate host plants,and the naturally occurring polyamines have potential applications in agriculture in developing protection strategies for crops from RKN infection.

Regulation of Root-Knot Nematode Behavior by Seed-Coat Mucilage-Derived Attractants

Seed exudates influence the behavior of soil organisms,but howthis occurs remains unclear,particularly for multicellular animals.Here we show that compounds associated with Arabidopsis seed-coat mucilage regulate the behavior of soil-borne animals,specifically root-knot nematodes (RKNs).Infective RKN J2 larvae actively travel toward Arabidopsis seeds through chemotaxis.Analysis of Arabidopsis mucilage mutants demonstrated that the attraction of RKNs toArabidopsis seeds requires the synthesis and extrusion of.seed-coat mucilage.Extracted mucilage alone is not sufficient to attract RKNs,but seed-surface carbohydrates and proteins are required for this process.These findings suggest that the RKN chemoattractant is synthesized de novo upon mucilage extrusion but may be highly unstable.RKNs attracted by thismucilage-dependent mechanism can infect the emerging seedling.However,the attraction signal from seedling roots likely acts independently of the seed-coat signal and may mask the attraction to seed-coat mucilage after germination.Multiple RKN species are attracted byArabidopsis seeds,suggesting that this mechanism is conserved in RKNs.These findings indicate that seed exudate can regulate the behavior of multicellular animals and highlight the potential roles of seed-coat mucilage in biotic interactions with soil microorganisms.