Biomedical subjects

J Stephen Gantt

Publications and source records attributed to J Stephen Gantt.

4 recordsLinked to original sources

PubMed2007

A transient decrease in reactive oxygen species in roots leads to root hair deformation in the legume-rhizobia symbiosis.

* A possible role for reactive oxygen species (ROS) in root hair deformation in response to Nod factor (NF) was investigated using Medicago truncatula nodulation mutants, and an inhibitor and precursors of ROS. * In wild-type roots, ROS efflux transiently decreased approximately 1 h after NF treatment. Transcript accumulation of two NADPH oxidase homologs, respiratory burst oxidase homolog 2 (MtRBOH2) and MtRBOH3, also transiently decreased at 1 h. However, in the nonnodulating mutant Nod factor perception (nfp), transcript accumulation did not change. * Exogenous application of ROS prevented root hair swelling and branching induced by NF. When accumulation of ROS was prevented by diphenylene iodonium (DPI), NF did not induce root hair branching. Root treatment with DPI alone reduced ROS efflux and induced root hair tip swelling. Transient treatment of roots with DPI mimicked NF treatment and resulted in root hair branching in the absence of NF. A transient DPI treatment did not induce root hair branching in the nonlegumes Arabidopsis thaliana and tomato (Lycopersicon esculentum). * The results suggest a role for the transient reduction of ROS accumulation in governing NF-induced root hair deformation in legumes.

Arabidopsis↗

PubMed2006

Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula.

Legume rhizobia symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture and in the Earth's nitrogen cycle. Signaling between rhizobia and legumes initiates development of a unique plant organ, the root nodule, where bacteria undergo endocytosis and become surrounded by a plant membrane to form a symbiosome. Between this membrane and the encased bacteria exists a matrix-filled space (the symbiosome space) that is thought to contain a mixture of plant- and bacteria-derived proteins. Maintenance of the symbiosis state requires continuous communication between the plant and bacterial partners. Here, we show in the model legume Medicago truncatula that a novel family of six calmodulin-like proteins (CaMLs), expressed specifically in root nodules, are localized within the symbiosome space. All six nodule-specific CaML genes are clustered in the M. truncatula genome, along with two other nodule-specific genes, nodulin-22 and nodulin-25. Sequence comparisons and phylogenetic analysis suggest that an unequal recombination event occurred between nodulin-25 and a nearby calmodulin, which gave rise to the first CaML, and the gene family evolved by tandem duplication and divergence. The data provide striking evidence for the recruitment of a ubiquitous Ca(2+)-binding gene for symbiotic purposes.

Base Sequence↗

PubMed2005

RNA interference identifies a calcium-dependent protein kinase involved in Medicago truncatula root development.

Changes in cellular or subcellular Ca2+ concentrations play essential roles in plant development and in the responses of plants to their environment. However, the mechanisms through which Ca2+ acts, the downstream signaling components, as well as the relationships among the various Ca2+-dependent processes remain largely unknown. Using an RNA interference-based screen for gene function in Medicago truncatula, we identified a gene that is involved in root development. Silencing Ca2+-dependent protein kinase1 (CDPK1), which is predicted to encode a Ca2+-dependent protein kinase, resulted in significantly reduced root hair and root cell lengths. Inactivation of CDPK1 is also associated with significant diminution of both rhizobial and mycorrhizal symbiotic colonization. Additionally, microarray analysis revealed that silencing CDPK1 alters cell wall and defense-related gene expression. We propose that M. truncatula CDPK1 is a key component of one or more signaling pathways that directly or indirectly modulates cell expansion or cell wall synthesis, possibly altering defense gene expression and symbiotic interactions.

Arabidopsis Proteins↗

PubMed2002

Genome-wide identification of nodule-specific transcripts in the model legume Medicago truncatula.

The Medicago truncatula expressed sequence tag (EST) database (Gene Index) contains over 140,000 sequences from 30 cDNA libraries. This resource offers the possibility of identifying previously uncharacterized genes and assessing the frequency and tissue specificity of their expression in silico. Because M. truncatula forms symbiotic root nodules, unlike Arabidopsis, this is a particularly important approach in investigating genes specific to nodule development and function in legumes. Our analyses have revealed 340 putative gene products, or tentative consensus sequences (TCs), expressed solely in root nodules. These TCs were represented by two to 379 ESTs. Of these TCs, 3% appear to encode novel proteins, 57% encode proteins with a weak similarity to the GenBank accessions, and 40% encode proteins with strong similarity to the known proteins. Nodule-specific TCs were grouped into nine categories based on the predicted function of their protein products. Besides previously characterized nodulins, other examples of highly abundant nodule-specific transcripts include plantacyanin, agglutinin, embryo-specific protein, and purine permease. Six nodule-specific TCs encode calmodulin-like proteins that possess a unique cleavable transit sequence potentially targeting the protein into the peribacteroid space. Surprisingly, 114 nodule-specific TCs encode small Cys cluster proteins with a cleavable transit peptide. To determine the validity of the in silico analysis, expression of 91 putative nodule-specific TCs was analyzed by macroarray and RNA-blot hybridizations. Nodule-enhanced expression was confirmed experimentally for the TCs composed of five or more ESTs, whereas the results for those TCs containing fewer ESTs were variable.

Agglutinins↗