We report the complete 6,530,228-bp genome sequence of the symbiotic nitrogen fixing bacterium Rhizobium etli. Six large plasmids comprise one-third of the total genome size. The chromosome encodes most functions necessary for cell growth, whereas few essential genes or complete metabolic pathways are located in plasmids. Chromosomal synteny is disrupted by genes related to insertion sequences, phages, plasmids, and cell-surface components. Plasmids do not show synteny, and their orthologs are mostly shared by accessory replicons of species with multipartite genomes. Some nodulation genes are predicted to be functionally related with chromosomal loci encoding for the external envelope of the bacterium. Several pieces of evidence suggest an exogenous origin for the symbiotic plasmid (p42d) and p42a. Additional putative horizontal gene transfer events might have contributed to expand the adaptive repertoire of R. etli, because they include genes involved in small molecule metabolism, transport, and transcriptional regulation. Twenty-three putative sigma factors, numerous isozymes, and paralogous families attest to the metabolic redundancy and the genomic plasticity necessary to sustain the lifestyle of R. etli in symbiosis and in the soil. multireplicon genome ͉ rhizobiales ͉ symbiosis ͉ horizontal transfer

The Transporter Classification Database (TCDB; tcdb.org) is a freely accessible reference resource, which provides functional, structural, mechanistic, medical and biotechnological information about transporters from organisms of all types. TCDB is the only transport protein classification database adopted by the International Union of Biochemistry and Molecular Biology (IUBMB) and now (October 1, 2020) consists of 20 653 proteins classified in 15 528 non-redundant transport systems with 1567 tabulated 3D structures, 18 336 reference citations describing 1536 transporter families, of which 26% are members of 82 recognized superfamilies. Overall, this is an increase of over 50% since the last published update of the database in 2016. This comprehensive update of the database contents and features include (i) adoption of a chemical ontology for substrates of transporters, (ii) inclusion of new superfamilies, (iii) a domain-based characterization of transporter families for the identification of new members as well as functional and evolutionary relationships between families, (iv) development of novel software to facilitate curation and use of the database, (v) addition of new subclasses of transport systems including 11 novel types of channels and 3 types of group translocators and (vi) the inclusion of many man-made (artificial) transmembrane pores/channels and carriers.

Although common bean (Phaseolus vulgaris) is the most important grain legume in the developing world for human consumption, few genomic resources exist for this species. The objectives of this research were to develop expressed sequence tag (EST) resources for common bean and assess nodule gene expression through high-density macroarrays. We sequenced a total of 21,026 ESTs derived from 5 different cDNA libraries, including nitrogen-fixing root nodules, phosphorus-deficient roots, developing pods, and leaves of the Mesoamerican genotype, Negro Jamapa 81. The fifth source of ESTs was a leaf cDNA library derived from the Andean genotype, G19833. Of the total high-quality sequences, 5,703 ESTs were classified as singletons, while 10,078 were assembled into 2,226 contigs producing a nonredundant set of 7,969 different transcripts. Sequences were grouped according to 4 main categories, metabolism (34%), cell cycle and plant development (11%), interaction with the environment (19%), and unknown function (36%), and further subdivided into 15 subcategories. Comparisons to other legume EST projects suggest that an entirely different repertoire of genes is expressed in common bean nodules. Phaseolus-specific contigs, gene families, and single nucleotide polymorphisms were also identified from the EST collection. Functional aspects of individual bean organs were reflected by the 20 contigs from each library composed of the most redundant ESTs. The abundance of transcripts corresponding to selected contigs was evaluated by RNA blots to determine whether gene expression determined by laboratory methods correlated with in silico expression. Evaluation of root nodule gene expression by macroarrays and RNA blots showed that genes related to nitrogen and carbon metabolism are integrated for ureide production. Resources developed in this project provide genetic and genomic tools for an international consortium devoted to bean improvement.

Our laboratory has developed bioinformatic strategies for identifying distant phylogenetic relationships and characterizing families and superfamilies of transport proteins. Results using these tools suggest that the Anoctamin Superfamily of cation and anion channels, as well as lipid scramblases, includes three functionally characterized families: the Anoctamin (ANO), Transmembrane Channel (TMC) and Ca2+-permeable Stress-gated Cation Channel (CSC) families; as well as four families of functionally uncharacterized proteins, which we refer to as the Anoctamin-like (ANO-L), Transmembrane Channel-like (TMC-L), and CSC-like (CSC-L1 and CSC-L2) families. We have constructed protein clusters and trees showing the relative relationships among the seven families. Topological analyses suggest that the members of these families have essentially the same topologies. Comparative examination of these homologous families provides insight into possible mechanisms of action, indicates the currently recognized organismal distributions of these proteins, and suggests drug design potential for the disease-related channel proteins.

Correspondence: Guillermo Dávila. E-mail: davila@cifn.unam.mx. © 2003 González et al.; licensee BioMed CentralLtd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL. The mosaic structure of the symbiotic plasmid of Rhizobium etli CFN42 and its relation to other symbiotic genome compartments The symbiotic plasmid is a circular molecule of 371,255 base-pairs containing 359 coding sequences. Nodulation and nitrogen-fixation genes common to other rhizobia are clustered in a region of 125 kilobases. Numerous sequences related to mobile elements are scattered throughout. In some cases the mobile elements flank blocks of functionally related sequences, thereby suggesting a role in transposition. The plasmid contains 12 reiterated DNA families that are likely to participate in genomic rearrangements. Comparisons between this plasmid and complete rhizobial genomes and symbiotic compartments already sequenced show a general lack of synteny and colinearity, with the exception of some transcriptional units. There are only 20 symbiotic genes that are shared by all SGCs. AbstractBackground: Symbiotic bacteria known as rhizobia interact with the roots of legumes and induce the formation of nitrogen-fixing nodules. In rhizobia, essential genes for symbiosis are compartmentalized either in symbiotic plasmids or in chromosomal symbiotic islands. To understand the structure and evolution of the symbiotic genome compartments (SGCs), it is necessary to analyze their common genetic content and organization as well as to study their differences. To date, five SGCs belonging to distinct species of rhizobia have been entirely sequenced. We report the complete sequence of the symbiotic plasmid of Rhizobium etli CFN42, a microsymbiont of beans, and a comparison with other SGC sequences available.