Description: This article discusses root architecture and nodulation. Abstract: The Medicago truncatula LATD/NIP gene is essential for the development of lateral and primary root and nitrogen-fixing nodule meristems as well as for rhizobial invasion of nodules. LATD/NIP encodes a member of the NRT1(PTR1) nitrate and di-and tri-peptide transporter family, suggesting that its function is to transport one of these or another compound(s). Because latd/nip mutants can have their lateral and primary root defects rescued by ABA, ABA is a potential substrate for transport. LATD/NIP expression in the root meristem was demonstrated to be regulated by auxin, cytokinin and abscisic acid, but not by nitrate. LATD/NIP's potential function and its role in coordinating root architecture and nodule formation are discussed.

Description: This presentation discusses research on searching for the genes that encode nodulation symbiosis between medicago truncatula and rhizobia. Rhizobia are a group of bacteria that interact with legumes to produce ammonia. They receive glucose and fix nitrogen for the plant so the plant is able to create the amino acids and Nucleic acids required for growth. This presentation explains the research and the physical mapping, cross over events in propogation, and genetic mapping

Description: This article discusses multiple domains in MtENOD8 protein. Symbiotic nitrogen fixation occurs in nodules, specialized organs on the roots of legumes. Within nodules, host plant cells are infected with rhizobia that are encapsulated by a plant-derived membrane forming a novel organelle, the symbiosome. In Medicago truncatula, the symbiosome consists of the symbiosome membrane (SymM), a single rhizobium, and the soluble space between them, called the symbiosome space (Syms). The SymS is enriched with plant-derived proteins, including the MtENOD8 protein. Here, the authors present evidence from GFP fusion experiments that the MtENOD8 protein contains at least three symbiosome targeting domains, including its N-terminal signal peptide (SP). When ectopically expressed in non-nodulated root tissue, the MtENOD8 SP delivers GFP to the vacuole. During the course of nodulation, there is a nodule-specific re-direction MtENOD8-SP-GFP from the vacuole to punctate intermediates and subsequently to symbiosomes, with re-direction of MtENOD8-SP-GFP from the vacuole to punctate intermediates preceding intracellular rhizobial infection. Experiments with Medicago mutants having defects in rhizobial infection and symbiosome development demonstrated that the MtNIP/LATD gene is required for re-direction of the MtENOD8-SP-GFP from the vacuoles to punctate intermediates in nodules. The authors' evidence shows that MtENOD8 has evolved redundant targeting sequences for symbiosome ...

Description: This article discusses a functional assessment of the Medicago truncatula NIP/LATD. Abstract: The Medicago truncatula NIP/LATD (for Numerous Infections and Polyphenolics/Lateral root-organ Defective) gene encodes a protein found in a clade of nitrate transporters within the large NRT1(PTR) family that also encodes transporters of dipeptides and tripeptides, dicarboxylates, auxin, and abscisic acid. Of the NRT1(PTR) members known to transport nitrate, most are low-affinity transporters. Here, the authors show that M. truncatula nip/latd mutants are more defective in their lateral root responses to nitrate provided at low (250 μм) concentrations than at higher (5mм) concentrations; however, nitrate uptake experiments showed no discernible differences in uptake in the mutants. Heterologous expression experiments showed that MtNIP/LATD encodes a nitrate transporter: expression in Xenopus laevis oocytes conferred upon the oocytes the ability to take up nitrate from the medium, but oocytes expressing the less severe Mtnip-3 allele were proficient in nitrate transport. M. truncatula nip/latd mutants have pleiotropic defects in nodulation and root architecture defects but not for nodulation defects. This suggests that the spectrum of activities inherent in AtNRT1.1 is different from that possessed by MtNIP/LATD, but it could also reflect stability differences of each protein in M. truncatula. Collectively, the data show ...

Description: This article discusses a putative transporter for integrating nutrient and hormone signaling with lateral root growth and nodule development in Medicago truncatula. Legume root architecture involves not only elaboration of the root system by the formation of lateral roots but also the formation of symbiotic root nodules in association with nitrogen-fixing soil rhizobia. The Medicago truncatula LATD/NIP gene plays an essential role in the development of both primary and lateral roots as well as nodule development. We have cloned the LATD/NIP gene and show that it encodes a member of the NRT1(PTR) transporter family. LATD/NIP is expressed throughout the plant. pLATD/NIP-GFP promoter-reporter fusions in transgenic roots establish the spatial expression of LATD/NIP in primary root, lateral root and nodule meristems and the surrounding cells. Expression of LATD/NIP is regulated by hormones, in particular by abscisic acid which has been previously shown to rescue the primary and lateral root meristem arrest of latd mutants. latd mutants respond normally to ammonium but have defects in responses of the root architecture to nitrate. Taken together, these results suggest that LATD/NIP may encode a nitrate transporter or transporter of another compound.