Siderophores in plant root tissue: Tagetes patula nana colonized by the arbuscular mycorrhizal fungus Gigaspora margarita

More than 70% of vascular plant species live in symbiosis with arbuscular mycorrhizal (AM) fungi. In addition to other effects this symbiosis is known for its significance for plant nutrition including iron. Fungal iron mobilization from soil is commonly dependent on siderophores. This study reports on a search for such iron-chelators in root tissue of Tagetes patula nana var. plena colonized by Gigaspora margarita. The AM colonized plants and uninoculated controls were grown under strictly axenic conditions. HPLC analyses of aqueous extracts from plant roots have provided clear evidence for the presence of a rhizoferrin type siderophore, named glomuferrin, in root tissue of mycorrhizal seedlings. Results from HPLC analytical work are seconded by molecular biological data: A BLASTp search revealed that the AM fungal species Gigaspora rosea, Rhizophagus irregularis (formerly Glomus intraradices), Glomus cerebriformis and Diversispora epigea encode a non-ribosomal peptide synthetase (NRPS)-independent siderophore synthase (NIS), which is homologous to the rhizoferrin synthetase of Rhizopus delemar. Thus this study indicates that the biosynthesis of rhizoferrin type siderophores such as glomuferrin (= bis-imidorhizoferrin) may be widespread in the AM symbiosis.