RESUMEN
Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and glomeromycete fungi. It is the most widespread terrestrial plant symbiosis, improving plant uptake of water and mineral nutrients. Yet, despite its crucial role in land ecosystems, molecular mechanisms leading to its formation are just beginning to be unravelled. Recent evidence suggests that AM fungi produce diffusible symbiotic signals. Here we show that Glomus intraradices secretes symbiotic signals that are a mixture of sulphated and non-sulphated simple lipochitooligosaccharides (LCOs), which stimulate formation of AM in plant species of diverse families (Fabaceae, Asteraceae and Umbelliferae). In the legume Medicago truncatula these signals stimulate root growth and branching by the symbiotic DMI signalling pathway. These findings provide a better understanding of the evolution of signalling mechanisms involved in plant root endosymbioses and will greatly facilitate their molecular dissection. They also open the way to using these natural and very active molecules in agriculture.
Asunto(s)
Lipopolisacáridos/metabolismo , Micorrizas/metabolismo , Raíces de Plantas/metabolismo , Raíces de Plantas/microbiología , Simbiosis , Secuencia de Carbohidratos , Cromatografía Líquida de Alta Presión , Daucus carota/química , Daucus carota/metabolismo , Daucus carota/microbiología , Glomeromycota/metabolismo , Lipopolisacáridos/química , Medicago truncatula/química , Medicago truncatula/crecimiento & desarrollo , Medicago truncatula/metabolismo , Medicago truncatula/microbiología , Datos de Secuencia Molecular , Extractos Vegetales/química , Extractos Vegetales/metabolismo , Raíces de Plantas/química , Raíces de Plantas/crecimiento & desarrollo , Transducción de Señal , Esporas Fúngicas/química , Esporas Fúngicas/metabolismoAsunto(s)
Proteínas Portadoras/genética , Genoma de Planta , Fosfoproteínas/genética , Proteínas de Plantas/genética , Solanum tuberosum/genética , Proteínas Portadoras/química , Evolución Molecular , Fabaceae/genética , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Familia de Multigenes , Fosfoproteínas/química , Proteínas de Plantas/química , Populus/genética , Solanum tuberosum/químicaRESUMEN
We set up a large-scale suppression subtractive hybridization (SSH) approach to identify Medicago truncatula genes differentially expressed at different stages of the symbiotic interaction with Sinorhizobium meliloti, with a particular interest for regulatory genes. We constructed 7 SSH libraries covering successive stages from Nod factor signal transduction to S. meliloti infection, nodule organogenesis, and functioning. Over 26,000 clones were differentially screened by two rounds of macroarray hybridizations. In all, 3,340 clones, corresponding to genes whose expression was potentially affected, were selected, sequenced, and ordered into 2,107 tentative gene clusters, including 767 MtS clusters corresponding to new M. truncatula genes. In total, 52 genes encoding potential regulatory proteins, including transcription factors (TFs) and other elements of signal transduction cascades, were identified. The expression pattern of some of them was analyzed by quantitative reverse-transcription polymerase chain reaction in wild-type and in Nod- M. truncatula mutants blocked before or after S. meliloti infection. Three genes, coding for TFs of the bHLH and WRKY families and a C2H2 zinc-finger protein, respectively, were found to be upregulated, following S. meliloti inoculation, in the infection-defective mutant lin, whereas the bHLH gene also was expressed in the root-hair-curling mutant hcl. The potential role of these genes in early symbiotic steps is discussed.