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The genes encoding malate synthase (glcB) and isocitrate lyase (aceA) and a 240-bp open reading frame (SMc00767) located downstream ofaceA were isolated and functionally characterized in Sinorhizobium meliloti. Independent and double interposon mutants of each gene were constructed, and the corresponding phenotypes were analyzed, aceA mutants failed to grow on acetate, and mutants deficient in SMc00767 were also affected in acetate utilization. In contrast, mutants deficient in glcB grew on acetate similar to wild-type strain Rm5000. Complementation experiments showed that aceA and SMc00767 gene constructs were able to restore the growth on acetate in the corresponding single mutants, aceA-glcB, aceA-SMc00767, and glcB-SMc00767 double knockouts were also unable to grow on acetate, but this ability was recovered when the wild-type aceA-glcB or aceA-SMc00767 loci were introduced into the double mutants. These data confirm the functional role of aceA and SMc00767 and show that glcB, in the absence of SMc00767, is required for acetate metabolism. Isocitrate lyase and malate synthase activities were measured in strain Rm5000, the mutant derivatives, and complemented strains, aceA and glcB were able to complement the enzymatic activity lacking in the corresponding single mutants. The enzymatic activities also showed that SMc00767 represses the activity of isocitrate lyase in cells grown on acetate. Gene fusions confirmed the repressor role of SMc00767, which regulates aceA expression at the transcriptional level. Comparison of the transcriptional profiles of the SMc00767 mutant and wild-type strain Rm5000 showed that SMc00767 represses the expression of a moderate number of open reading frames, including aceA; thus, we propose that SMc00767 is a novel repressor involved in acetate metabolism in S. meliloti. Genetic and functional analyses indicated that aceA and SMc00767 constitute a functional two-gene operon, which is conserved in other [alpha]-proteobacteria. Alfalfa plants infected with the aceA and glcB mutants were not impaired in nodulation or nitrogen fixation, and so the glyoxylate cycle is not required in the Rhizobium-legume symbiosis.

Birdsfoot trefoil (Lotus corniculatus L.) is a highly variable and widely distributed Old-World perennial forage legume found in wild and naturalized populations throughout temperate regions of Europe, Asia Minor, North Africa, North and South America, Australia, and New Zealand. Understanding the relationships among birdsfoot trefoil morphologic, ecogeographic, and genetic characteristics may provide insights for better utilizing exotic germplasm. The objectives of this research were to (i) compare morphologic and random amplified polymorphic DNA (RAPD) classifications of 28 exotic and ecologically diverse genotypes from the USDA National Plant Germplasm System (NPGS) birdsfoot trefoil collection, and (ii) determine the relationships between genotype classifications and collecting-site ecogeographic features. Eighteen morphologic characteristics, 130 RAPD bands, and eight collecting-site ecogeographic characteristics were used to classify the genotypes. The relatedness of genetic, morphologic, ecologic, and geographic distances among the genotypes was measured using the product moment correlation. Genotype morphology was related to collecting-site distances from one another and ecologic similarity. Genetic relatedness was also associated with collecting-site ecology, and specific morphologic characteristics were associated with different ecogeographic features. The similarity between the genetic and ecologic classifications suggested that genotypes adapted to similar habitats, even if geographically distant, have acquired similar phenotypes. Since RAPD descriptors were associated with the ecologic similarity of genotype collecting sites but not with their geographic closeness, classifications of birdsfoot trefoil should rely on both ecogeographic and morphologic characteristics of accessions., THE GENUS Lotus is a large polymorphic and widely distributed group that comprises approximately 200 annual and perennial species (Grant, 1965). Birdsfoot trefoil is generally reported to have 2n = [...]

Birdsfoot trefoil (Lotus corniculatus L.) is a widely distributed polymorphic Old-World perennial forage legume found in wild and naturalized populations throughout temperate regions of Europe, Asia Minor, North Africa, and North and South America. Exotic birdsfoot trefoil germplasm has rarely been used for birdsfoot trefoil genetic enhancement, and information about its crossing ability with other exotics and commercial quality germplasm is not available. The objectives of this research were to (i) characterize the crossing ability of 27 exotic birdsfoot trefoil genotypes with two genetically diverse hybridization testers, and (ii) determine if crossing ability among genotypes was related to their genetic background measured by random amplified polymorphic DNA (RAPD) markers and their ecogeographic origins. Crossing ability was determined using reciprocal crosses with one commercial-quality germplasm and one exotic genotype tester. All possible crossing combinations for an eight-genotype subset were also determined. Crossing ability was measured as the percentage of pollinated flowers that set pods, [F.sub.1] progeny pollen viability, pod length, and seeds per pod. Self-genotype pod set and pollen viability were not correlated. Intermediate bridge crosses were identified that could potentially overcome specific cross incompatibilities and be used to obtain progeny for any combination of genotypes. Genotype-crossing ability was associated with ecogeographic features of the collecting site, but not with morphologic characteristics. This differs from findings that other genotype morphologic characteristics are associated with ecogeographic origins and genetic similarities based on RAPD markers. Exotic birdsfoot trefoil genotypes can be utilized with commercial-quality germplasm using conventional crossing methods., BIRDSFOOT TREFOIL a perennial, non-bloating, forage legume that has valuable attributes making it a good alternative to other legumes in temperate regions. It is adapted to slightly acidic, droughty, infertile, [...]