Characterization of genes involved in the autoregulation of nodulation in chickpea (Cicer arietinum L.)

Establishment of an excess number of nodules markedly affects plant growth and development due to overconsumption of photosynthates for nitrogen fixation. Hence, the total root nodule number must be tightly controlled via a negative feedback mechanism (AON) to maintain an optimal nitrogen and carbon balance in chickpea plants. Chickpea genes whichplay important regulatory roles in root nodulation in chickpea (Cicer arietinum) were identified by aligning these genes with known genes of legumes available at phytozome through BLAST search. Chickpea nodulation genes identified and characterized in this study include CaNFR1/5, CaENOD40, CaNARK, CaRIC1, CaRIC2, CaNIC1, CaRDN1, CaRDN2, CaRDN3, CamiRNA172 and CaNNC1. These genes were orthologous to Medicago truncatula nodulation genes and were significantly expressed by inoculating chickpea plants with Mesorhizobium ciceri analysed by qRT-PCR using RNA isolated from the root and leaf tissues of inoculated chickpea plants at 0, 2, and 6 days after inoculation. Non-inoculated plants served as control. CaNARK genes were expressed in roots and leaves while the rest of the nodulation genes were expressed only in the roots. The nodulation ability of chickpea may be controlled by an internal AON mechanism which involves several genes that are orthologues with other legumes.

Draft Genome Sequence of Bradyrhizobium elkanii Strain SEMIA 938, Used in Commercial Inoculants for Lupinus spp. in Brazil

Due to its high capacity for nitrogen fixation, strain SEMIA 938 is used in commercial inoculants for lupins in Brazil. Its genome was estimated at 8,780,064 bp and indicates that it belongs to the Bradyrhizobium elkanii species, while the analysis of nodulation genes classifies the strain in the symbiovar sojae.

Genome Sequence of Rhizobium esperanzae Type Strain CNPSo 668, Isolated from Phaseolus vulgaris Nodules in Mexico

ABSTRACT Rhizobium esperanzae CNPSo 668T is a nitrogen-fixing symbiont of Phaseolus vulgaris isolated from Mexican soils. Its genome is estimated at 6,294,057 bp, with 6,219 coding sequences (CDSs) showing higher similarity (92.9%) with Rhizobium etli. Three copies of the regulatory nodD, in addition to other nodulation genes, should define its host specificity.

Biogeographical Patterns of Legume-Nodulating Burkholderia spp.: from African Fynbos to Continental Scales

ABSTRACTRhizobia of the genusBurkholderiahave large-scale distribution ranges and are usually associated with South African papilionoid and South American mimosoid legumes, yet little is known about their genetic structuring at either local or global geographic scales. To understand variation at different spatial scales, from individual legumes in the fynbos (South Africa) to a global context, we analyzed chromosomal (16S rRNA,recA) and symbiosis (nifH,nodA,nodC) gene sequences. We showed that the global diversity of nodulation genes is generally grouped according to the South African papilionoid or South American mimosoid subfamilies, whereas chromosomal sequence data were unrelated to biogeography. While nodulation genes are structured on a continental scale, a geographic or host-specific distribution pattern was not detected in the fynbos region. In host range experiments, symbiotic promiscuity ofBurkholderiatuberumSTM678TandB.phymatumSTM815Twas discovered in selected fynbos species. Finally, a greenhouse experiment was undertaken to assess the ability of mimosoid (Mimosapudica) and papilionoid (Dipogonlignosus,Indigoferafilifolia,Macroptiliumatropurpureum, andPodalyriacalyptrata) species to nodulate in South African (fynbos) and Malawian (savanna) soils. While theBurkholderia-philous fynbos legumes (D.lignosus,I.filifolia, andP.calyptrata) nodulated only in their native soils, the invasive neotropical speciesM.pudicadid not develop nodules in the African soils. The fynbos soil, notably rich inBurkholderia, seems to retain nodulation genes compatible with the local papilionoid legume flora but is incapable of nodulating mimosoid legumes that have their center of diversity in South America.IMPORTANCEThis study is the most comprehensive phylogenetic assessment of root-nodulatingBurkholderiaand investigated biogeographic and host-related patterns of the legume-rhizobial symbiosis in the South African fynbos biome, as well as at global scales, including native species from the South American Caatinga and Cerrado biomes. While a global investigation of the rhizobial diversity revealed distinct nodulation and nitrogen fixation genes among South African and South American legumes, regionally distributed species in the Cape region were unrelated to geographic and host factors.